@article{babar_khan_blount_barnett_harrison_dewitt_johnson_mergoum_boyles_murphy_et al._2024, title={Registration of 'FL16045-25': An early-maturing, high-yielding, disease-resistant soft red facultative wheat cultivar for the southern United States}, volume={4}, ISSN={["1940-3496"]}, DOI={10.1002/plr2.20343}, abstractNote={Abstract}, journal={JOURNAL OF PLANT REGISTRATIONS}, author={Babar, Md Ali and Khan, Naeem and Blount, Ann and Barnett, Ronald D. and Harrison, Stephen A. and Dewitt, Noah and Johnson, Jerry and Mergoum, Mohamed and Boyles, Rick and Murphy, Paul and et al.}, year={2024}, month={Apr} }
 @article{boyles_ballen-taborda_brown-guedira_costa_cowger_dewitt_griffey_harrison_ibrahim_johnson_et al._2023, title={Approaching 25 years of progress towards Fusarium head blight resistance in southern soft red winter wheat (Triticum aestivum L.)}, volume={8}, ISSN={["1439-0523"]}, DOI={10.1111/pbr.13137}, abstractNote={Abstract}, journal={PLANT BREEDING}, author={Boyles, Richard E. and Ballen-Taborda, Carolina and Brown-Guedira, Gina and Costa, Jose and Cowger, Christina and DeWitt, Noah and Griffey, Carl A. and Harrison, Stephen A. and Ibrahim, Amir and Johnson, Jerry and et al.}, year={2023}, month={Aug} }
 @article{adhikari_brown_ojiambo_cowger_2023, title={Effects of Host and Weather Factors on the Growth Rate of Septoria nodorum Blotch Lesions on Winter Wheat}, volume={5}, ISSN={["1943-7684"]}, url={https://doi.org/10.1094/PHYTO-12-22-0476-R}, DOI={10.1094/PHYTO-12-22-0476-R}, abstractNote={ Septoria nodorum blotch (SNB), caused by Parastagonospora nodorum, is a major disease of winter wheat that occurs frequently in the central and southeastern United States. Quantitative resistance to SNB in wheat is determined by various disease resistance components and their interaction with environmental factors. A study was conducted in North Carolina from 2018 to 2020 to characterize SNB lesion size and growth rate and to quantify the effects of temperature and relative humidity on lesion expansion in winter wheat cultivars with different levels of resistance. Disease was initiated in the field by spreading P. nodorum-infected wheat straw in experimental plots. Cohorts (groups of foliar lesions arbitrarily selected and tagged as an observational unit) were sequentially selected and monitored throughout each season. Lesion area was measured at regular intervals, and weather data were collected using in-field data loggers and the nearest weather stations. Final mean lesion area was approximately seven times greater on susceptible than on moderately resistant cultivars, and lesion growth rate was approximately four times higher on susceptible than on moderately resistant cultivars. Across trials and cultivars, temperature had a strong effect of increasing lesion growth rates ( P < 0.001), while relative humidity had no significant effect ( P = 0.34). Lesion growth rate declined slightly and steadily over the duration of cohort assessment. Our results demonstrate that restricting lesion growth is an important component of SNB resistance in the field and suggest that the ability to limit lesion size may be a useful breeding goal. }, journal={PHYTOPATHOLOGY}, author={Adhikari, Urmila and Brown, James and Ojiambo, Peter S. and Cowger, Christina}, year={2023}, month={May} }
 @article{adhikari_cowger_ojiambo_2023, title={Evaluation of a Model for Predicting Onset of Septoria nodorum Blotch in Winter Wheat}, volume={107}, ISSN={["1943-7692"]}, url={https://doi.org/10.1094/PDIS-06-22-1469-RE}, DOI={10.1094/PDIS-06-22-1469-RE}, abstractNote={ Prediction models that aid growers in making decisions on timing of fungicide application are important components of integrated management programs for several foliar diseases of wheat. The risk of Septoria nodorum blotch (caused by Parastagonospora nodorum) onset in winter wheat has been reported to be influenced by location, amount of wheat residue in the field, and cumulative daily infection values 2 weeks prior to day of year (DOY) 102. A model previously developed based on these predictor variables was evaluated for its ability to predict disease onset under field conditions. An experiment was conducted at three locations in North Carolina in 2018, 2019, and 2020, where plots were either treated with >20% wheat residue or received no residue treatment. Plots were monitored for disease symptoms, and disease onset was defined to have occurred when mean disease incidence in a plot was 50%. Of the 298 disease cases recorded, disease onset occurred early (i.e., prior to DOY 102) in 257 cases, while onset was late (i.e., on or after DOY 102) in 41 cases. Model accuracy based on correct classification ranged from 0.67 to 0.95, with a mean of 0.87 across the study period. Similarly, sensitivity rates of the model ranged from 0.88 to 1.0 with a mean of 0.98 across all years. However, the model had low specificity, with a mean rate of 0.15 across the study period. Overall, there was no significant difference in the frequency of observed and predicted cases in the study (χ2 = 0.50, P = 0.7788, df = 2). Time to disease onset was significantly correlated with grain yield and explained 26% of variation in yield (P < 0.0001). Results indicated that the disease onset model performs well in predicting early disease onset but requires further evaluation and improvement, particularly in the Piedmont, where it over-predicted early onset in 2 successive years. }, number={4}, journal={PLANT DISEASE}, author={Adhikari, Urmila and Cowger, Christina and Ojiambo, Peter S.}, year={2023}, month={Apr}, pages={1122–1130} }
 @article{hawkes_allen_balint-kurti_cowger_2023, title={Manipulating the plant mycobiome to enhance resilience: Ecological and evolutionary opportunities and challenges}, volume={19}, ISSN={["1553-7374"]}, DOI={10.1371/journal.ppat.1011816}, number={12}, journal={PLOS PATHOGENS}, author={Hawkes, Christine V. and Allen, Xavious and Balint-Kurti, Peter and Cowger, Christina}, year={2023}, month={Dec} }
 @article{cowger_read_clark_dong_2023, title={Optimal Timing of Fungicide Application to Manage Fusarium Head Blight in Winter Barley}, volume={4}, ISSN={["1943-7692"]}, url={https://doi.org/10.1094/PDIS-01-23-0021-RE}, DOI={10.1094/PDIS-01-23-0021-RE}, abstractNote={ Fusarium head blight (FHB) is among the chief threats to profitable barley production, and fungicide applications are one of two main strategies for reducing FHB damage to barley crops. However, there is very little published information on optimal timing of such applications. A 4-year field study was conducted with winter barley in Raleigh, North Carolina, to compare three timings for fungicide application: 50% spike emergence (Zadoks growth stage or GS 55), 100% spike emergence (GS 59), and 6 days after GS 59. Three winter barley cultivars with varying levels of FHB resistance were grown for four successive years (2018 to 2021) in a split-plot experiment and inoculated each spring with Fusarium-infected corn spawn. Three fungicides were compared: propiconazole + pydiflumetofen (Miravis Ace), prothioconazole + tebuconazole (Prosaro), and metconazole (Caramba). Correlations among visual symptoms and assays of harvested grain were modest and were weakened by fungicide applications. Across years and cultivars, deoxynivalenol (DON) and percent Fusarium-infected kernels were most reduced relative to the nontreated control by fungicide applications at the latest timing (GS 59 + 6 days). The early (GS 55) timing resulted in DON not significantly different from the nontreated control. Based on these results, it is recommended that to minimize damage from FHB, fungicide should be applied to winter barley several days after GS 59 (100% spike emergence), and not before GS 59. }, journal={PLANT DISEASE}, author={Cowger, Christina and Read, Quentin D. D. and Clark, Logan and Dong, Yanhong}, year={2023}, month={Apr} }
 @article{kloppe_whetten_kim_powell_lück_douchkov_whetten_hulse‐kemp_balint‐kurti_cowger_2023, title={Two pathogen loci determine <i>Blumeria graminis}, volume={238}, ISSN={0028-646X 1469-8137}, url={http://dx.doi.org/10.1111/nph.18809}, DOI={10.1111/nph.18809}, abstractNote={Summary}, number={4}, journal={New Phytologist}, publisher={Wiley}, author={Kloppe, Tim and Whetten, Rebecca B. and Kim, Saet‐Byul and Powell, Oliver R. and Lück, Stefanie and Douchkov, Dimitar and Whetten, Ross W. and Hulse‐Kemp, Amanda M. and Balint‐Kurti, Peter and Cowger, Christina}, year={2023}, month={Mar}, pages={1546–1561} }
 @article{mergoum_johnson_buck_buntin_sutton_lopez_mailhot_chen_bland_harrison_et al._2022, title={A new soft red winter wheat cultivar 'GA 08535-15LE29' adapted to Georgia and the US southeast region}, volume={5}, ISSN={["1940-3496"]}, DOI={10.1002/plr2.20235}, abstractNote={Abstract}, journal={JOURNAL OF PLANT REGISTRATIONS}, author={Mergoum, Mohamed and Johnson, Jerry and Buck, James and Buntin, G. David and Sutton, Steve and Lopez, Benjamin and Mailhot, Daniel and Chen, Zhenbang and Bland, Dan and Harrison, Stephen and et al.}, year={2022}, month={May} }
 @article{ackerman_holmes_gaskins_jordan_hicks_fitzgerald_griffey_mason_harrison_murphy_et al._2022, title={Evaluation of Methods for Measuring Fusarium-Damaged Kernels of Wheat}, volume={12}, ISSN={["2073-4395"]}, url={https://www.mdpi.com/2073-4395/12/2/532}, DOI={10.3390/agronomy12020532}, abstractNote={Fusarium head blight (FHB) is one of the most economically destructive diseases of wheat (Triticum aestivum L.), causing substantial yield and quality loss worldwide. Fusarium graminearum is the predominant causal pathogen of FHB in the U.S., and produces deoxynivalenol (DON), a mycotoxin that accumulates in the grain throughout infection. FHB results in kernel damage, a visual symptom that is quantified by a human observer enumerating or estimating the percentage of Fusarium-damaged kernels (FDK) in a sample of grain. To date, FDK estimation is the most efficient and accurate method of predicting DON content without measuring presence in a laboratory. For this experiment, 1266 entries collectively representing elite varieties and SunGrains advanced breeding lines encompassing four inoculated FHB nurseries were represented in the analysis. All plots were subjected to a manual FDK count, both exact and estimated, near-infrared spectroscopy (NIR) analysis, DON laboratory analysis, and digital imaging seed phenotyping using the Vibe QM3 instrument developed by Vibe imaging analytics. Among the FDK analytical platforms used to establish percentage FDK within grain samples, Vibe QM3 showed the strongest prediction capabilities of DON content in experimental samples, R2 = 0.63, and higher yet when deployed as FDK GEBVs, R2 = 0.76. Additionally, Vibe QM3 was shown to detect a significant SNP association at locus S3B_9439629 within major FHB resistance quantitative trait locus (QTL) Fhb1. Visual estimates of FDK showed higher prediction capabilities of DON content in grain subsamples than previously expected when deployed as genomic estimated breeding values (GEBVs) (R2 = 0.71), and the highest accuracy in genomic prediction, followed by Vibe QM3 digital imaging, with average Pearson’s correlations of r = 0.594 and r = 0.588 between observed and predicted values, respectively. These results demonstrate that seed phenotyping using traditional or automated platforms to determine FDK boast various throughput and efficacy that must be weighed appropriately when determining application in breeding programs to screen for and develop resistance to FHB and DON accumulation in wheat germplasms.}, number={2}, journal={AGRONOMY-BASEL}, author={Ackerman, Arlyn J. and Holmes, Ryan and Gaskins, Ezekiel and Jordan, Kathleen E. and Hicks, Dawn S. and Fitzgerald, Joshua and Griffey, Carl A. and Mason, Richard Esten and Harrison, Stephen A. and Murphy, Joseph Paul and et al.}, year={2022}, month={Feb} }
 @article{sotiropoulos_arango-isaza_ban_barbieri_bourras_cowger_ben-david_dinoor_ellwood_graf_et al._2022, title={Global genomic analyses of wheat powdery mildew reveal association of pathogen spread with historical human migration and trade}, volume={13}, ISSN={["2041-1723"]}, DOI={10.1038/s41467-022-31975-0}, abstractNote={Abstract}, number={1}, journal={NATURE COMMUNICATIONS}, author={Sotiropoulos, Alexandros G. and Arango-Isaza, Epifania and Ban, Tomohiro and Barbieri, Chiara and Bourras, Salim and Cowger, Christina and Ben-David, Roi and Dinoor, Amos and Ellwood, Simon R. and Graf, Johannes and et al.}, year={2022}, month={Jul} }
 @article{tini_covarelli_cowger_sulyok_benincasa_beccari_2022, title={Infection timing affects Fusarium poae colonization of bread wheat spikes and mycotoxin accumulation in the grain}, volume={6}, ISSN={["1097-0010"]}, DOI={10.1002/jsfa.12002}, abstractNote={Abstract}, journal={JOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE}, author={Tini, Francesco and Covarelli, Lorenzo and Cowger, Christina and Sulyok, Michael and Benincasa, Paolo and Beccari, Giovanni}, year={2022}, month={Jun} }
 @article{cowger_meyers_whetten_2022, title={Sensitivity of the US Wheat Powdery Mildew Population to Quinone Outside Inhibitor Fungicides and Determination of the Complete Blumeria graminis f. sp. tritici Cytochrome b Gene}, volume={112}, ISSN={["1943-7684"]}, url={https://doi.org/10.1094/PHYTO-04-21-0132-R}, DOI={10.1094/PHYTO-04-21-0132-R}, abstractNote={ Wheat powdery mildew, caused by Blumeria graminis f. sp. tritici, is managed primarily with cultivar resistance and foliar fungicides. Quinone outside inhibitors (QoIs), which target the mitochondrial cytochrome b (cytb) gene, are one of the two main fungicide classes used on wheat. While European populations of B. graminis f. sp. tritici are widely insensitive to QoIs, largely because of the cytb mutation G143A, the QoI sensitivity of the U.S. B. graminis f. sp. tritici population had never been evaluated despite years of QoI use on U.S. wheat. A total of 381 B. graminis f. sp. tritici isolates from 15 central and eastern U.S. states were screened for sensitivity to QoI fungicides pyraclostrobin and picoxystrobin. A modest range of sensitivities was observed, with maximum resistance factors of 11.2 for pyraclostrobin and 5.3 for picoxystrobin. The F129L, G137R, and G143A cytb mutations were not detected in the U.S. B. graminis f. sp. tritici population, nor were mutations identified in the PEWY loop, a key part of the Qo site. Thus, no genetic basis for the observed quantitative variation in QoI sensitivity of U.S. B. graminis f. sp. tritici was identified. Isolate sporulation was weakly negatively associated with reduced QoI sensitivity, suggesting a fitness cost. In the course of the study, the complete B. graminis f. sp. tritici cytb gene sequence was determined for the first time in the isolate 96224 v. 3.16 reference genome. Contrary to previous reports, the gene has an intron that appears to belong to intron group II, which is unusual in fungi. The study was the first QoI sensitivity screening of a large, geographically diverse set of U.S. B. graminis f. sp. tritici isolates, and while the population as a whole remains relatively sensitive, some quantitative loss of efficacy was observed. }, number={2}, journal={PHYTOPATHOLOGY}, author={Cowger, Christina and Meyers, Emily and Whetten, Rebecca}, year={2022}, month={Feb}, pages={249–260} }
 @article{kloppe_boshoff_pretorius_lesch_akin_morgounov_shamanin_kuhnem_murphy_cowger_2022, title={Virulence of Blumeria graminis f. sp. tritici in Brazil, South Africa, Turkey, Russia, and Australia}, volume={13}, ISSN={["1664-462X"]}, DOI={10.3389/fpls.2022.954958}, abstractNote={The globally distributed causal agent of powdery mildew on wheat, Blumeria graminis f. sp. tritici (Bgt), is one of the most rapidly adapting plant pathogens and requires monitoring for shifts in virulence to wheat resistance (Pm) genes. Virulence frequencies were assessed in a total of 346 Bgt isolates from several countries that had either lately recorded increasing powdery mildew epidemics (Brazil, South Africa, and Australia) or not recently been surveyed (Turkey and Russia). The results were compared to previously published surveys of United States and Egyptian Bgt (390 isolates). Many of the Pm genes that have potentially been employed longer (Pm1a–Pm17) were shown to have lost effectiveness, and the complexity of virulence to those genes was higher among Brazilian isolates than those from any other country. Some cases of high virulence frequency could be linked to specific Pm gene deployments, such as the widespread planting of cultivar Wyalkatchem (Pm1a) in Australia. Virulence was also assessed to a set of Pm genes recently introgressed from diploid and tetraploid wheat relatives into a hexaploid winter wheat background and not yet commercially deployed. The isolate collections from Fertile Crescent countries (Egypt and Turkey) stood out for their generally moderate frequencies of virulence to both the older and newer Pm genes, consistent with that region’s status as the center of origin for both host and pathogen. It appeared that the recently introgressed Pm genes could be the useful sources of resistance in wheat breeding for other surveyed regions.}, journal={FRONTIERS IN PLANT SCIENCE}, author={Kloppe, Tim and Boshoff, Willem and Pretorius, Zacharias and Lesch, Driecus and Akin, Beyhan and Morgounov, Alexey and Shamanin, Vladimir and Kuhnem, Paulo and Murphy, Paul and Cowger, Christina}, year={2022}, month={Aug} }
 @article{mergoum_johnson_buck_sutton_lopez_bland_chen_buntin_mailhot_babar_et al._2021, title={'GA JT141-14E45': A new soft red winter wheat cultivar adapted to Georgia and the US Southeast region}, volume={8}, ISSN={["1940-3496"]}, DOI={10.1002/plr2.20070}, abstractNote={Abstract}, journal={JOURNAL OF PLANT REGISTRATIONS}, author={Mergoum, Mohamed and Johnson, Jerry W. and Buck, James W. and Sutton, Steve and Lopez, Benjamin and Bland, Daniel and Chen, Z. and Buntin, G. D. and Mailhot, Daniel J. and Babar, Md A. and et al.}, year={2021}, month={Aug} }
 @article{mergoum_johnson_buck_sutton_lopez_bland_chen_buntin_mailhot_babar_et al._2021, title={A new soft red winter wheat cultivar, 'GA 07353-14E19', adapted to Georgia and the US Southeast environments}, volume={15}, ISSN={["1940-3496"]}, DOI={10.1002/plr2.20113}, abstractNote={Abstract}, number={2}, journal={JOURNAL OF PLANT REGISTRATIONS}, author={Mergoum, Mohamed and Johnson, Jerry W. and Buck, James W. and Sutton, Steve and Lopez, Benjamin and Bland, Daniel and Chen, Z. and Buntin, G. D. and Mailhot, Daniel J. and Babar, Md A. and et al.}, year={2021}, month={May}, pages={337–344} }
 @article{reeves_kerns_cowger_shew_2021, title={Pythium spp. Associated with Root Rot and Stunting of Winter Crops in North Carolina}, volume={105}, ISSN={["1943-7692"]}, DOI={10.1094/PDIS-11-20-2403-RE}, abstractNote={ Annual double-crop rotation systems that incorporate winter wheat, clary sage, or a cover crop are common in eastern North Carolina. Stunting and root rot of clary sage (Salvia sclarea L.) reduce yields of this crop, especially in wet soils. Stunting and reduced stand establishment also afflict winter cover crops, including rye, rapeseed, and winter pea. Pythium spp. are causal agents of root rot of winter wheat in this region, but their role in root rot and stunting of other winter crops is not understood. During the growing seasons of 2018 to 2019 and 2019 to 2020, samples of clary sage, rye, rapeseed, and winter pea displaying symptoms of stunting were collected across eastern North Carolina, resulting in the recovery of 420 isolates of Pythium from the roots of all hosts. Pythium irregulare, Pythium spinosum, and the complex Pythium sp. cluster B2A were the species most frequently isolated from clary sage. P. irregulare and P. spinosum were aggressive pathogens of clary sage at 18°C and caused moderate root rot at 28°C. Koch’s postulates confirmed that isolates belonging to Pythium sp. cluster B2A, Pythium sylvaticum, Pythium pachycaule, Pythium aphanidermatum, Pythium myriotylum, and Pythium oopapillum are pathogens of clary sage. P. irregulare (37% of all isolates) and members of the species complex Pythium sp. cluster B2A (28% of all isolates) constituted the majority of isolates collected from all hosts and were the species most frequently isolated from rye, rapeseed, and winter pea. In pathogenicity assays, isolates representing P. irregulare and P. spinosum caused slight to moderate root necrosis on rye, rapeseed, and winter pea. Isolates representing Pythium sp. cluster B2A caused slight to moderate root necrosis on rapeseed and clary sage, but no symptoms on rye or winter pea. }, number={11}, journal={PLANT DISEASE}, author={Reeves, Ella R. and Kerns, James P. and Cowger, Christina and Shew, Barbara B.}, year={2021}, month={Nov}, pages={3433–3442} }
 @article{reeves_kerns_cowger_shew_2021, title={Pythium spp. Associated with Root Rot and Stunting of Winter Wheat in North Carolina}, volume={105}, ISSN={["1943-7692"]}, url={https://doi.org/10.1094/PDIS-09-20-2022-RE}, DOI={10.1094/PDIS-09-20-2022-RE}, abstractNote={ In eastern North Carolina, mild to severe stunting and root rot have reduced yields of winter wheat, especially during years with abundant rainfall. Causal agents of root rot of wheat in this region were previously identified as Pythium irregulare, P. vanterpoolii, and P. spinosum. To investigate species prevalence, 114 isolates of Pythium were obtained from symptomatic wheat plants collected in eight counties. Twelve species were recovered, with P. irregulare (32%), P. vanterpoolii (17%), and P. spinosum (16%) the most common. Pathogenicity screens were performed with selected isolates of each species, and slight to severe necrosis of young roots was observed. The aggressiveness of five isolates each of P. irregulare, P. vanterpoolii, and P. spinosum was compared on a single cultivar of wheat at 14°C, and very aggressive isolates were found within all species. In vitro growth of these isolates was measured at 14 and 20°C, and all isolates grew faster at the warmer temperature. The effects of varying temperatures and rates of nitrogen on root rot caused by Pythium spp. alone or in combination were investigated. All inoculation treatments caused severe root rot under all conditions tested, and disease was more severe at 12 and 14°C compared with 18 and 20°C; however, there was no effect of nitrogen application. }, number={4}, journal={PLANT DISEASE}, author={Reeves, Ella R. and Kerns, James P. and Cowger, Christina and Shew, Barbara B.}, year={2021}, month={Apr}, pages={986–996} }
 @article{mergoum_johnson_buck_sutton_lopez_bland_chen_buntin_mailhot_babar_et al._2021, title={Soft red winter wheat 'GA 051207-14E53': Adapted cultivar to Georgia and the US Southeast region}, volume={15}, ISSN={["1940-3496"]}, DOI={10.1002/plr2.20102}, abstractNote={Abstract}, number={1}, journal={JOURNAL OF PLANT REGISTRATIONS}, author={Mergoum, Mohamed and Johnson, Jerry W. and Buck, James W. and Sutton, Steve and Lopez, Benjamin and Bland, Daniel and Chen, Z. and Buntin, G. D. and Mailhot, Daniel J. and Babar, Md A. and et al.}, year={2021}, month={Jan}, pages={132–139} }
 @article{xue_lim_chen_humphreys_cao_menzies_cowger_li_serajazari_2021, title={Virulence structure of Blumeria graminis f. sp. tritici, the causal agent of wheat powdery mildew, in Ontario, Canada, in 2018 and 2019}, volume={5}, ISSN={["1715-2992"]}, DOI={10.1080/07060661.2021.1915876}, abstractNote={Abstract Powdery mildew caused by Blumeria graminis f. sp. tritici (Bgt) is a major disease of wheat (Triticum aestivum) in Ontario, which can cause 20% yield loss. The development of resistant commercial wheat cultivars is the most economical means of controlling this disease, but only if the resistance genes used are incompatible with the virulence phenotypes present in the pathogen population. The virulence structure of Bgt in Ontario was examined in 2018 and 2019. Of the 42 single colony isolates collected in Ontario greenhouses and commercial fields, 40 virulence phenotypes, assigned VP1 to VP40, were identified on a set of 24 single-gene differential genotypes. Of the 24 resistance genes possessed by the differential genotypes, eight genes including Pm1a, Pm1b, Pm1c, Pm12, Pm16, Pm21, Pm37, and MlAG12 were effective against all of the Bgt isolates. Four genes including Pm3d, Pm29, Pm34, and NCAG13 were mostly effective with resistance reactions to more than 80% of the isolates. There were no significant differences in numbers of virulence genes per isolate between the two years, or between the greenhouse and field origins. The virulence frequencies of Bgt isolates for these effective and mostly effective genes were also not significantly affected by the year of collection and their origins, suggesting that the Bgt population is relatively stable. The effective genes identified in this study may be deployed singly or used for gene pyramiding in wheat breeding programs for developing powdery mildew-resistant cultivars in Ontario.}, journal={CANADIAN JOURNAL OF PLANT PATHOLOGY}, author={Xue, Allen G. and Lim, Seara and Chen, Yuanhong and Humphreys, Gavin and Cao, Wenguang and Menzies, Jim and Cowger, Christina and Li, Hongjie and Serajazari, Mitra}, year={2021}, month={May} }
 @article{cowger_smith_boos_bradley_ransom_bergstrom_2020, title={Managing a Destructive, Episodic Crop Disease: A National Survey of Wheat and Barley Growers' Experience With Fusarium Head Blight}, volume={104}, ISSN={["1943-7692"]}, url={https://doi.org/10.1094/PDIS-10-18-1803-SR}, DOI={10.1094/PDIS-10-18-1803-SR}, abstractNote={ The main techniques for minimizing Fusarium head blight (FHB, or scab) and deoxynivalenol in wheat and barley are well established and generally available: planting of moderately FHB-resistant cultivars, risk monitoring, and timely use of the most effective fungicides. Yet the adoption of these techniques remains uneven across the FHB-prone portions of the U.S. cereal production area. A national survey was undertaken by the U.S. Wheat and Barley Scab Initiative in 17 states where six market classes of wheat and barley are grown. In 2014, 5,107 usable responses were obtained. The highest percentages reporting losses attributable to FHB in the previous 5 years were in North Dakota, Maryland, Kentucky, and states bordering the Great Lakes but across all states, ≥75% of respondents reported no FHB-related losses in the previous 5 years. Adoption of cultivar resistance was uneven by state and market class and was low except among hard red spring wheat growers. In 13 states, a majority of respondents had not applied an FHB-targeted fungicide in the previous 5 years. Although the primary FHB information source varied by state, crop consultants were considered to be an important source or their primary source of information on risk or management of FHB by the largest percentage of respondents. Use of an FHB risk forecasting website was about twice as high in North Dakota as the 17-state average of 6%. The most frequently cited barriers to adopting FHB management practices were weather or logistics preventing timely fungicide application, difficulty in determining flowering timing for fungicide applications, and the impracticality of FHB-reducing rotations. The results highlight the challenges of managing an episodically damaging crop disease and point to specific areas for improvement. }, number={3}, journal={PLANT DISEASE}, publisher={Scientific Societies}, author={Cowger, Christina and Smith, Joy and Boos, Dennis and Bradley, Carl A. and Ransom, Joel and Bergstrom, Gary C.}, year={2020}, month={Mar}, pages={634–648} }
 @article{cowger_ward_nilsson_arellano_mccormick_busman_2020, title={Regional and field-specific differences in Fusarium species and mycotoxins associated with blighted North Carolina wheat}, volume={323}, ISSN={["1879-3460"]}, url={https://doi.org/10.1016/j.ijfoodmicro.2020.108594}, DOI={10.1016/j.ijfoodmicro.2020.108594}, abstractNote={Worldwide, while Fusarium graminearum is the main causal species of Fusarium head blight (FHB) in small-grain cereals, a diversity of FHB-causing species belonging to different species complexes has been found in most countries. In the U.S., FHB surveys have focused on the Fusarium graminearum species complex (FGSC) and the frequencies of 3-ADON, 15-ADON, and nivalenol (NIV) chemotypes. A large-scale survey was undertaken across the state of North Carolina in 2014 to explore the frequency and distribution of F. graminearum capable of producing NIV, which is not monitored at grain intake points. Symptomatic wheat spikes were sampled from 59 wheat fields in 24 counties located in three agronomic zones typical of several states east of the Appalachian Mountains: Piedmont, Coastal Plain, and Tidewater. Altogether, 2197 isolates were identified to species using DNA sequence-based methods. Surprisingly, although F. graminearum was the majority species detected, species in the Fusarium tricinctum species complex (FTSC) that produce "emerging mycotoxins" were frequent, and even dominant in some fields. The FTSC percentage was 50–100% in four fields, 30–49% in five fields, 20–29% in five fields, and < 20% in the remaining 45 fields. FTSC species were at significantly higher frequency in the Coastal Plain than in the Piedmont or Tidewater (P < .05). Moniliformin concentrations in samples ranged from 0.0 to 38.7 μg g−1. NIV producing isolates were rare statewide (2.2%), and never >12% in a single field, indicating that routine testing for NIV is probably unnecessary. The patchy distribution of FTSC species in wheat crops demonstrated the need to investigate the potential importance of their mycotoxins and the factors that allow them to sometimes outcompete trichothecene producers. An increased sampling intensity of wheat fields led to the unexpected discovery of a minority FHB-causing population.}, journal={INTERNATIONAL JOURNAL OF FOOD MICROBIOLOGY}, publisher={Elsevier BV}, author={Cowger, Christina and Ward, Todd J. and Nilsson, Kathryn and Arellano, Consuelo and McCormick, Susan P. and Busman, Mark}, year={2020}, month={Jun} }
 @article{cowger_ward_brown-guedira_brown_2020, title={Role of Effector-Sensitivity Gene Interactions and Durability of Quantitative Resistance to Septoria Nodorum Blotch in Eastern US Wheat}, volume={11}, ISSN={["1664-462X"]}, DOI={10.3389/fpls.2020.00155}, abstractNote={Important advances have been made in understanding the relationship of necrotrophic effectors (NE) and host sensitivity (Snn) genes in the Parastagonospora nodorum-wheat pathosystem. Yet much remains to be learned about the role of these interactions in determining wheat resistance levels in the field, and there is mixed evidence on whether breeding programs have selected against Snn genes due to their role in conferring susceptibility. SNB occurs ubiquitously in the U.S. Atlantic seaboard, and the environment is especially well suited to field studies of resistance to natural P. nodorum populations, as there are no other important wheat leaf blights. Insights into the nature of SNB resistance have been gleaned from multi-year data on phenotypes and markers in cultivars representative of the region’s germplasm. In this perspective article, we review the evidence that in this eastern region of the U.S., wheat cultivars have durable quantitative SNB resistance and Snn–NE interactions are of limited importance. This conclusion is discussed in light of the relevant available information from other parts of the world.}, journal={FRONTIERS IN PLANT SCIENCE}, author={Cowger, Christina and Ward, Brian and Brown-Guedira, Gina and Brown, James K. M.}, year={2020}, month={Mar} }
 @article{anderson_freije_bergstrom_bradley_cowger_faske_hollier_kleczewski_padgett_paul_et al._2020, title={Sensitivity of Fusarium graminearum to Metconazole and Tebuconazole Fungicides Before and After Widespread Use in Wheat in the United States}, volume={21}, ISSN={["1535-1025"]}, DOI={10.1094/PHP-11-19-0083-RS}, abstractNote={ Fusarium head blight (FHB) caused primarily by Fusarium graminearum, is a major disease of wheat in the United States. FHB is managed in part by applications of demethylation inhibitor (DMI) triazole fungicides during anthesis. The objective of this study was to examine the sensitivity of U.S. populations of F. graminearum to the DMI triazole fungicides metconazole and tebuconazole. Isolates of F. graminearum collected from wheat between 1981 and 2014 were tested for fungicide sensitivity using mycelial growth assays to determine the effective concentration at which 50% of fungal growth was inhibited (EC50). A total of 45 isolates were tested for metconazole sensitivity and 47 for sensitivity to tebuconazole. Isolates were analyzed in groups based on collection date. Groupings consisted of isolates collected prior to widespread fungicide use in wheat (designated as year 2000) or after fungicides became available for use in wheat. The mean EC50 for isolates collected prior to 2000 was 0.0240 µg/ml for metconazole and 0.1610 µg/ml for tebuconazole. For both fungicides, isolates collected between 2000 and 2014 had significantly higher (P = 0.05) mean EC50 values (mean EC50 = 0.0405 and 0.3311 µg/ml for metconazole and tebuconazole, respectively) compared with isolates collected prior to 2000. Isolate, year, and state of collection all affected the mean EC50 values of isolates collected between 2000 and 2014. A single isolate collected from Illinois in 2012 exhibited EC50 values of 0.1734 µg/ml for metconazole and 1.7339 µg/ml for tebuconazole, indicating reduced sensitivity compared with the mean EC50 of other isolates collected between 2000 and 2014. This study is the first step toward developing a fungicide sensitivity monitoring program for F. graminearum in the United States. }, number={2}, journal={PLANT HEALTH PROGRESS}, author={Anderson, Nolan R. and Freije, Anna N. and Bergstrom, Gary C. and Bradley, Carl A. and Cowger, Christina and Faske, Travis and Hollier, Clayton and Kleczewski, Nathan and Padgett, Guy B. and Paul, Pierce and et al.}, year={2020}, pages={85–90} }
 @article{cowger_beccari_dong_2020, title={Timing of Susceptibility to Fusarium Head Blight in Winter Wheat}, volume={104}, ISSN={["1943-7692"]}, url={https://doi.org/10.1094/PDIS-03-20-0527-RE}, DOI={10.1094/PDIS-03-20-0527-RE}, abstractNote={ The duration of wheat susceptibility to Fusarium infection has implications for risk forecasting, fungicide timing, and the likelihood that visible kernel damage may underpredict deoxynivalenol (DON) contamination. A field experiment was conducted to explore the impact of varying infection timings on Fusarium head blight (FHB) development in winter wheat. Trials in four successive years (2010 to 2013) in North Carolina utilized one susceptible and one moderately resistant cultivar possessing similar maturity, stature, and grain quality. Inoculum was applied in the form of sprayed Fusarium graminearum conidia. In the first year, the nine infection timings were from 0 to 21 days after anthesis (daa), whereas in the following 3 years, they ranged from 0 to 13 daa. Infection progression was compared among inoculation timings by sampling spikes five to six times during grain-fill. Based on DON, percent kernel damage and kernel infection, and fungal spread as assayed via qPCR, the moderately resistant cultivar had at least a 2- to 3-day shorter window of susceptibility to damaging FHB infection than the susceptible cultivar. The results suggest that duration of susceptibility is an important aspect of cultivar resistance to FHB. In 2012, the window of susceptibility for both cultivars was extended by cold snaps during anthesis. After debranning in one year, the majority of DON was found to be in the bran fraction of kernels; there was also a trend for later infections to lead to a higher percentage of DON in the nonbran fraction, as well as a higher ratio of DON to FDK. }, number={11}, journal={PLANT DISEASE}, publisher={Scientific Societies}, author={Cowger, Christina and Beccari, Giovanni and Dong, Yanhong}, year={2020}, month={Nov}, pages={2928–2939} }
 @article{mckee_cowger_dill-macky_friskop_gautam_ransom_wilson_2019, title={Disease Management and Estimated Effects on DON (Deoxynivalenol) Contamination in Fusarium Infested Barley}, volume={9}, url={https://doi.org/10.3390/agriculture9070155}, DOI={10.3390/agriculture9070155}, abstractNote={Fusarium head blight (FHB or scab) economically devastates barley production. FHB is predominantly caused by Fusarium graminearum and has resulted in major reductions in the quality of barley in the United States. The most common source of economic loss is through development of potent mycotoxins in the grain, the most prominent of which, in the United States, is deoxynivalenol (DON). DON levels can be managed through a variety of techniques. This study presents the estimate of the statistical relationship among DON contamination in barley, FHB incidence and severity, and a variety of disease management techniques. Data from 22 field studies and a survey of barley producers are used to estimate the relationship. Fungicide applications reduce DON in barley in general and via complementary interactions with the barley cultivar. Genetic FHB resistance in barley varieties is an important determinant of DON levels, as well as previous crop and factors related to time and location. Taking care to avoid rotations with FHB host crops immediately prior to barley is also important to reduce DON levels in barley. These become key inputs into barley producer decisions for evaluating the economic value of adopting FHB management techniques.}, number={7}, journal={Agriculture}, publisher={MDPI AG}, author={McKee, Gregory and Cowger, Christina and Dill-Macky, Ruth and Friskop, Andrew and Gautam, Pravin and Ransom, Joel and Wilson, William}, year={2019}, month={Jul}, pages={155} }
 @article{cowger_brown_2019, title={Durability of Quantitative Resistance in Crops: Greater Than We Know?}, volume={57}, ISSN={["1545-2107"]}, DOI={10.1146/annurev-phyto-082718-100016}, abstractNote={Quantitative resistance (QR) to crop diseases has usually been much more durable than major-gene, effector-triggered resistance. It has been observed that the effectiveness of some QR has eroded as pathogens adapt to it, especially when deployment is extensive and epidemics occur regularly, but it generally declines more slowly than effector-triggered resistance. Changes in aggressiveness and specificity of diverse pathogens on cultivars with QR have been recorded, along with experimental data on fitness costs of pathogen adaptation to QR, but there is little information about molecular mechanisms of adaptation. Some QR has correlated or antagonistic effects on multiple diseases. Longitudinal data on cultivars’ disease ratings in trials over several years can be used to assess the significance of QR for durable resistance in crops. It is argued that published data likely underreport the durability of QR, owing to publication bias. The implications of research on QR for plant breeding are discussed.}, journal={ANNUAL REVIEW OF PHYTOPATHOLOGY, VOL 57, 2019}, author={Cowger, Christina and Brown, James K. M.}, year={2019}, pages={253–277} }
 @article{beccari_arellano_covarelli_tini_sulyok_cowger_2019, title={Effect of wheat infection timing on Fusarium head blight causal agents and secondary metabolites in grain}, volume={290}, ISSN={["1879-3460"]}, url={https://doi.org/10.1016/j.ijfoodmicro.2018.10.014}, DOI={10.1016/j.ijfoodmicro.2018.10.014}, abstractNote={Fusarium head blight (FHB) results in yield loss and damaging contamination of cereal grains and can be caused by several Fusarium species. The objective of the present study was to determine, in a greenhouse experiment on winter wheat, how FHB was affected by timing of infection (0, 3, 6 or 9 days after anthesis, daa) by the aggressive species Fusarium graminearum compared to the relatively weak species Fusarium avenaceum, Fusarium poae and Fusarium acuminatum. Measures of FHB development were: symptoms in spikes (visually assessed), fungal biomass (quantified by real time quantitative PCR) and accumulation of fungal secondary metabolites (quantified by liquid chromatography-tandem mass spectrometry) in kernels. With regard to symptoms, F. graminearum was unaffected by inoculation timing, while the weaker pathogens caused greater disease severity at later timings. In contrast, the accumulation of F. graminearum biomass was strongly affected by inoculation timing (3 daa ≥ 6 daa ≥ 0 daa = 9 daa), while colonization by the weaker pathogens was less influenced. Similarly, F. graminearum secondary metabolite accumulation was affected by inoculation timing (3 daa ≥ 6 daa ≥ 0 daa = 9 daa), while that of the weaker species was less affected. However, secondary metabolites produced by these weaker species tended to be higher from intermediate-late inoculations (6 daa). Overall, infection timing appeared to play a role particularly in F. graminearum colonization and secondary metabolite accumulation. However, secondary metabolites of weaker Fusarium species may be relatively more abundant when environmental conditions promote spore dispersal later in anthesis, while secondary metabolites produced by F. graminearum are relatively favored by earlier conducive conditions.}, journal={INTERNATIONAL JOURNAL OF FOOD MICROBIOLOGY}, publisher={Elsevier BV}, author={Beccari, Giovanni and Arellano, Consuelo and Covarelli, Lorenzo and Tini, Francesco and Sulyok, Michael and Cowger, Christina}, year={2019}, month={Feb}, pages={214–225} }
 @article{richards_stukenbrock_carpenter_liu_cowger_faris_friesen_2019, title={Local adaptation drives the diversification of effectors in the fungal wheat pathogen Parastagonospora nodorum in the United States}, volume={5}, url={https://doi.org/10.1101/657007}, DOI={10.1101/657007}, abstractNote={Abstract}, publisher={Cold Spring Harbor Laboratory}, author={Richards, Jonathan K. and Stukenbrock, Eva H. and Carpenter, Jessica and Liu, Zhaohui and Cowger, Christina and Faris, Justin D. and Friesen, Timothy L.}, year={2019}, month={May} }
 @article{richards_stukenbrock_carpenter_liu_cowger_faris_friesen_2019, title={Local adaptation drives the diversification of effectors in the fungal wheat pathogen Parastagonospora nodorum in the United States}, volume={15}, url={https://doi.org/10.1371/journal.pgen.1008223}, DOI={10.1371/journal.pgen.1008223}, abstractNote={Filamentous fungi rapidly evolve in response to environmental selection pressures, exemplified by their genomic plasticity. Parastagonospora nodorum, a fungal pathogen of wheat and causal agent of septoria nodorum blotch, responds to selection pressure exerted by its host, influencing the gain, loss, or functional diversification of putative effector genes. Whole genome resequencing of 197 P. nodorum isolates collected from spring, durum, and winter wheat production regions of the United States enabled the examination of effector diversity and genomic regions under selection specific to geographically discrete populations. A total of 1,026,859 quality SNPs/InDels were identified within the natural population. Implementation of GWAS identified novel loci, as well as SnToxA and SnTox3 as major factors in disease. Genes displaying presence/absence variation and predicted effector genes, as well as genes localized on an accessory chromosome, had significantly higher pN/pS ratios, indicating a greater level of diversifying selection. Population structure analyses indicated two major P. nodorum populations corresponding to the Upper Midwest (Population 1) and Southern/Eastern United States (Population 2). Prevalence of SnToxA varied greatly between the two populations which correlated with presence of the host sensitivity gene Tsn1. Additionally, 12 and 5 candidate effector genes were observed to be diversifying among isolates from Population 1 and Population 2, respectively, but under purifying or neutral selection in the opposite population. Selective sweep analysis revealed 10 and 19 regions of positive selection from Population 1 and Population 2, respectively, with 92 genes underlying population-specific selective sweeps. Also, genes exhibiting presence/absence variation were significantly closer to transposable elements. Taken together, these results indicate that P. nodorum is rapidly adapting to distinct selection pressures unique to spring and winter wheat production regions by various routes of genomic diversification, potentially facilitated through transposable element activity. Author Summary Parastagonospora nodorum is an economically important pathogen of wheat, employing proteinaceous effector molecules to cause disease. Recognition of effectors by host susceptibility genes often leads to the elicitation of programmed cell death. However, little is known on the correlation between effector diversity and the spatial distribution of host resistance/susceptibility or the genomic mechanisms of diversification. This research presents the genome resequencing of 197 P. nodorum isolates collected from spring, winter, and durum wheat production regions of the United States, enabling the investigation of genome dynamics and evolution. Results illustrate local adaptation to host resistance or susceptibility, as evidenced by population-specific evolution of predicted effector genes and positively selected selective sweeps. Predicted effector genes, genes exhibiting presence/absence variation, and genes residing on an accessory chromosome, were found to be diversifying more rapidly. Additionally, transposable elements were predicted to play a role in the maintenance or elimination of genes. A GWAS approach identified the previously reported SnToxA and SnTox3 as well as novel virulence candidates, as major elicitors of disease on winter wheat. These results highlight the flexibility of the P. nodorum genome in response to population-specific selection pressures and illustrates the utility of whole genome resequencing for the identification of putative virulence mechanisms.}, number={10}, journal={PLOS Genetics}, publisher={Public Library of Science (PLoS)}, author={Richards, Jonathan K. and Stukenbrock, Eva H. and Carpenter, Jessica and Liu, Zhaohui and Cowger, Christina and Faris, Justin D. and Friesen, Timothy L.}, editor={Matute, Daniel REditor}, year={2019}, month={Oct}, pages={e1008223} }
 @article{cowger_arellano_marshall_fitzgerald_2019, title={Managing Fusarium Head Blight in Winter Barley With Cultivar Resistance and Fungicide}, volume={103}, ISSN={["1943-7692"]}, url={https://doi.org/10.1094/PDIS-09-18-1582-RE}, DOI={10.1094/PDIS-09-18-1582-RE}, abstractNote={ Although there has been research on managing Fusarium head blight (FHB) in spring barley, little has been published on cultivar resistance and optimal fungicide timing for FHB management in winter barley. A 3-year (2015 to 2017) field experiment was conducted to measure FHB resistance of winter barley varieties, gauge the potential benefit from a fungicide, and help determine the optimal timing for fungicide application. The split-plot experiment took place in a misted, inoculated nursery in Raleigh, North Carolina using main plots of four winter barley cultivars (Atlantic, Endeavor, Nomini, and Thoroughbred). Three fungicide treatments were applied to subplots: prothioconazole + tebuconazole at full spike emergence, the same fungicide 6 days later, or no fungicide. The late applications significantly reduced FHB index in each of 3 years and significantly reduced deoxynivalenol (DON) in harvested grain in 2 of the 3 years. Applications at full spike emergence also yielded significant benefit in 1 of the 3 years for each parameter. Neither disease symptoms nor DON gave reason to prefer one of the fungicide timings over the other. Across the 3 years, DON ranked the cultivars Endeavor < Nomini = Thoroughbred < Atlantic. Combining the moderate resistance of Endeavor with a fungicide application and averaging the two timings resulted in a 75% DON reduction compared with unsprayed Atlantic. Taken together, our results indicate that barley growers concerned about minimizing DON should both plant moderately resistant varieties and apply fungicide if there is scab risk. During the same period, 16 commercial winter barley cultivars were tested in from three to seven Virginia and North Carolina environments each, and the DON results were compared after standardization across environments. The winter two-row malting barley cultivars Endeavor and Calypso displayed superior and robust DON resistance across environments. }, number={8}, journal={PLANT DISEASE}, publisher={Scientific Societies}, author={Cowger, Christina and Arellano, Consuelo and Marshall, David and Fitzgerald, Joshua}, year={2019}, month={Aug}, pages={1858–1864} }
 @article{meyers_arellano_cowger_2019, title={Sensitivity of the US Blumeria graminis f. sp. tritici Population to Demethylation Inhibitor Fungicides}, volume={103}, ISBN={1943-7692}, url={https://doi.org/10.1094/PDIS-04-19-0715-RE}, DOI={10.1094/PDIS-04-19-0715-RE}, abstractNote={ Wheat powdery mildew, caused by Blumeria graminis f. sp. tritici, is managed in the United States with cultivar resistance and foliar fungicides. Despite high levels of fungicide sensitivity in other cereal mildew populations, fungicide sensitivity of U.S. B. graminis f. sp. tritici has never been evaluated. Almost 400 B. graminis f. sp. tritici isolates were collected from 15 U.S. states over 2 years and phenotyped for sensitivity to two widely used demethylation inhibitor (DMI) fungicides, tebuconazole and prothioconazole. A large range of sensitivity to both DMIs was observed, with more insensitive isolates originating from the eastern United States (Great Lakes, Mid-Atlantic, and Southeast regions) and more sensitive isolates from central states (Plains region, Arkansas, and Missouri). Cross-resistance was indicated by a positive although weak association between tebuconazole and prothioconazole sensitivities at all levels of analysis (EC50 values, P < 0.0001). A possible fitness cost was also associated with prothioconazole insensitivity (P = 0.0307) when analyzed at the state population level. This is the first assessment of fungicide sensitivity in the U.S. B. graminis f. sp. tritici population, and it produced evidence of regional selection for reduced DMI efficacy. The observation of reduced sensitivity to DMI fungicides in the eastern United States underlines the importance of rotating between chemistry classes to maintain the effectiveness of DMIs in U.S. wheat production. Although cross-resistance was demonstrated, variability in the relationship of EC50 values for tebuconazole and prothioconazole also suggests that multiple mechanisms influence B. graminis f. sp. tritici isolate responses to these two DMI fungicides. }, number={12}, journal={PLANT DISEASE}, publisher={Scientific Societies}, author={Meyers, Emily and Arellano, Consuelo and Cowger, Christina}, year={2019}, month={Dec}, pages={3108–3116} }
 @article{mcnally_menardo_luthi_praz_mueller_kunz_ben-david_chandrasekhar_dinoor_cowger_et al._2018, title={Distinct domains of the AVRPM3(A2/F2) avirulence protein from wheat powdery mildew are involved in immune receptor recognition and putative effector function}, volume={218}, ISSN={["1469-8137"]}, DOI={10.1111/nph.15026}, abstractNote={Summary}, number={2}, journal={NEW PHYTOLOGIST}, author={McNally, Kaitlin Elyse and Menardo, Fabrizio and Luthi, Linda and Praz, Coraline Rosalie and Mueller, Marion Claudia and Kunz, Lukas and Ben-David, Roi and Chandrasekhar, Kottakota and Dinoor, Amos and Cowger, Christina and et al.}, year={2018}, month={Apr}, pages={681–695} }
 @article{ceron-bustamante_ward_kelly_vaughan_mccormick_cowger_leyva-mir_villasenor-mir_ayala-escobar_nava-diaz_2018, title={Regional differences in the composition of Fusarium Head Blight pathogens and mycotoxins associated with wheat in Mexico}, volume={273}, ISSN={["1879-3460"]}, DOI={10.1016/j.ijfoodmicro.2018.03.003}, abstractNote={Fusarium Head Blight (FHB) is a destructive disease of small grain cereals and a major food safety concern. Epidemics result in substantial yield losses, reduction in crop quality, and contamination of grains with trichothecenes and other mycotoxins. A number of different fusaria can cause FHB, and there are significant regional differences in the occurrence and prevalence of FHB pathogen species and their associated mycotoxins. Information on FHB pathogen and mycotoxin diversity in Mexico has been extremely limited, but is needed to improve disease and mycotoxin control efforts. To address this, we used a combination of DNA sequence-based methods and in-vitro toxin analyses to characterize FHB isolates collected from symptomatic wheat in Mexico during the 2013 and 2014 growing seasons. Among 116 Fusarium isolates, we identified five species complexes including nine named Fusarium species and 30 isolates representing unnamed or potentially novel species. Significant regional differences (P < 0.001) in pathogen composition were observed, with F. boothii accounting for >90% of isolates from the Mixteca region in southern Mexico, whereas F. avenaceum and related members of the F. tricinctum species complex (FTSC) accounted for nearly 75% of isolates from the Highlands region in Central Mexico. F. graminearum, which is the dominant FHB pathogen in other parts of North America, was not present among the isolates from Mexico. F. boothii isolates had the 15-acetyldeoxynivalenol toxin type, and some of the minor FHB species produced trichothecenes, such as nivalenol, T-2 toxin and diacetoxyscirpenol. None of the FTSC isolates tested was able to produce trichothecenes, but many produced chlamydosporol and enniatin B.}, journal={INTERNATIONAL JOURNAL OF FOOD MICROBIOLOGY}, author={Ceron-Bustamante, Minely and Ward, Todd J. and Kelly, Amy and Vaughan, Martha M. and McCormick, Susan P. and Cowger, Christina and Leyva-Mir, Santos G. and Villasenor-Mir, Hector E. and Ayala-Escobar, Victoria and Nava-Diaz, Cristian}, year={2018}, month={May}, pages={11–19} }
 @article{wiersma_whetten_zhang_sehgal_kolb_poland_mason_carter_cowger_olson_2018, title={Registration of Two Wheat Germplasm Lines Fixed for Pm58}, volume={12}, ISSN={["1940-3496"]}, DOI={10.3198/jpr2017.06.0036crg}, abstractNote={Powdery mildew is a persistent threat to global wheat (Triticum aestivum L.) production. To broaden the genetic base for resistance to powdery mildew in wheat, germplasm lines U6714‐A‐011 (Reg. No. GP‐1023, PI 682090) and U6714‐B‐056 (Reg. No. GP‐1022, PI 682089) were developed at Michigan State University and are fixed for the novel powdery mildew resistance gene Pm58. This gene was identified in Aegilops tauschii Coss. accession TA1662, introgressed, and mapped to wheat chromosome 2DS. The two germplasm lines described are BC2F4–derived inbred backcrossed lines from a direct cross between TA1662 and the recurrent wheat parent KS05HW14, a hard white winter wheat line adapted to western Kansas. In addition to exhibiting resistant reactions to multiple Bgt isolates with broad virulence profiles, both lines have moderate yield potential and good agronomic characteristics, making them suitable as breeding germplasm. The availability of these lines will enable the incorporation of Pm58 into wheat breeding programs, providing additional genetic variation for resistance to powdery mildew.}, number={2}, journal={JOURNAL OF PLANT REGISTRATIONS}, author={Wiersma, Andrew T. and Whetten, Rebecca B. and Zhang, Guorong and Sehgal, Sunish K. and Kolb, Frederic L. and Poland, Jesse A. and Mason, R. Esten and Carter, Arron H. and Cowger, Christina and Olson, Eric L.}, year={2018}, month={May}, pages={270–273} }
 @article{ficke_cowger_bergstrom_brodal_2018, title={Understanding Yield Loss and Pathogen Biology to Improve Disease Management: Septoria Nodorum Blotch - A Case Study in Wheat}, volume={102}, ISSN={["1943-7692"]}, DOI={10.1094/pdis-09-17-1375-fe}, abstractNote={ The estimated potential yield losses caused by plant pathogens is up to 16% globally and most research in plant pathology aims to reduce yield loss in our crops directly or indirectly. Yield losses caused by a certain disease depend not only on disease severity, but also on the weather factors, the pathogen’s aggressiveness, and the ability of the crop to compensate for reduced photosynthetic area. The yield loss-disease relationship in a certain host-pathogen system might therefore change from year to year, making predictions for yield loss very difficult at the regional or even at the farmer’s level. However, estimating yield losses is essential to determine disease management thresholds at which acute control measures such as fungicide applications, or strategic measures such as crop rotation or use of resistant cultivars are economically and environmentally sensible. Legislation in many countries enforces implementation of integrated pest management (IPM), based on economic thresholds at which the costs due to a disease justify the costs for its management. Without a better understanding of the relationship between disease epidemiology and yield loss, we remain insufficiently equipped to design adequate IPM strategies that will be widely adapted in agriculture. Crop loss studies are resource demanding and difficult to interpret for one particular disease, as crops are usually not invaded by only one pest or pathogen at a time. Combining our knowledge on disease epidemiology, crop physiology, yield development, damage mechanisms involved, and the effect of management practices can help us to increase our understanding of the disease-crop loss relationship. The main aim of this paper is to review and analyze the literature on a representative host-pathogen relationship in an important staple food crop to identify knowledge gaps and research areas to better assess yield loss and design management strategies based on economic thresholds. }, number={4}, journal={PLANT DISEASE}, author={Ficke, Andrea and Cowger, Christina and Bergstrom, Gary and Brodal, Guro}, year={2018}, month={Apr}, pages={696–707} }
 @article{cowger_mehra_arellano_meyers_murphy_2018, title={Virulence Differences in Blumeria graminis f. sp tritici from the Central and Eastern United States}, volume={108}, ISSN={["1943-7684"]}, DOI={10.1094/phyto-06-17-0211-r}, abstractNote={ Wheat powdery mildew is a disease of global importance that occurs across a wide geographic area in the United States. A virulence survey of Blumeria graminis f. sp. tritici, the causal agent, was conducted by sampling 36 wheat fields in 15 U.S. states in the years 2013 and 2014. Using a hierarchical sampling protocol, isolates were derived from three separated plants at each of five separated sites within each field in order to assess the spatial distribution of pathotypes. In total, 1,017 isolates from those fields were tested individually on single-gene differential cultivars containing a total of 21 powdery mildew resistance (Pm) genes. Several recently introgressed mildew resistance genes from wild wheat relatives (Pm37, Pm53, MlAG12, NCAG13, and MlUM15) exhibited complete or nearly complete resistance to all local B. graminis f. sp. tritici populations from across the sampled area. One older gene, Pm4b, also retained at least some efficacy across the sampled area. The B. graminis f. sp. tritici population sampled from Arkansas and Missouri, on the western edge of the eastern soft red winter wheat region, had virulence profiles more similar to other soft wheat mildew populations than to the geographically closer population from hard wheat fields in the Plains states of Oklahoma, Nebraska, and Kansas. The Plains population differed in that it was avirulent to several Pm genes long defeated in the soft-wheat-growing areas. Virulence complexity was greatest east of the Mississippi River, and diminished toward the west. Several recently introgressed Pm genes (Pm25, Pm34, Pm35, and NCA6) that are highly effective against mildew in the field in North Carolina were unexpectedly susceptible to eastern-U.S. B. graminis f. sp. tritici populations in detached-leaf tests. Sampled fields displayed a wide range of pathotype diversity and spatial distribution, suggesting that epidemics are caused by varying numbers of pathotypes in all regions. The research confirmed that most long-used Pm genes are defeated in the eastern United States, and the U.S. B. graminis f. sp. tritici population has different virulence profiles in the hard- and soft-wheat regions, which are likely maintained by host selection, isolation by distance, and west-to-east gene flow. }, number={3}, journal={PHYTOPATHOLOGY}, author={Cowger, Christina and Mehra, Lucky and Arellano, Consuelo and Meyers, Emily and Murphy, J. Paul}, year={2018}, month={Mar}, pages={402–411} }
 @article{abdelrhim_abd-alla_abdou_ismail_cowger_2018, title={Virulence of Egyptian Blumeria graminis f. sp tritici Population and Response of Egyptian Wheat Cultivars}, volume={102}, ISSN={["1943-7692"]}, DOI={10.1094/pdis-07-17-0975-re}, abstractNote={ Powdery mildew, caused by Blumeria graminis (DC.) Speer f. sp. tritici (Em. Marchal), is a serious disease of wheat that can cause a large reduction in yield. In Egypt, high powdery mildew severity has been observed in the past few years on many commercial cultivars of both bread and durum wheat. Little information is available about virulence characteristics of the Egyptian B. graminis f. sp. tritici population in Egypt or the resistance of Egyptian wheat cultivars to powdery mildew. Virulence frequencies of a representative sample of the Egyptian B. graminis f. sp. tritici population were studied. Seven provinces were chosen to represent the country: two in Upper Egypt (Qena and Sohag), one in Middle Egypt (El Minia), and four in the north (Alexandria, Kafr Elsheikh, Dakahlia, and Sharqia). Ten isolates from each province (70 isolates total) were derived from single ascospores and used for this study. They were inoculated individually on 21 powdery mildew differential lines, each bearing a single resistance (Pm) gene. Also, the responses of 14 Egyptian bread wheat cultivars and 6 durum cultivars to each of the 70 isolates were evaluated individually. Among all tested Pm genes, only seven (Pm1b, Pm2, Pm21, Pm34, Pm36, Pm37, and Pm53) were effective against B. graminis f. sp. tritici isolates from all provinces. Several other genes were effective against most or all isolates from a majority of provinces. All tested bread wheat cultivars showed full susceptibility to all isolates, whereas two durum wheat cultivars, Beni-Suef-5 and Beni-Suef-6, had intermediate responses to a large percentage of the isolates, likely indicating partial resistance. To enhance mildew resistance in Egyptian wheat cultivars, it is recommended to use combinations of genes that are nationally effective or effective against multiple provincial B. graminis f. sp. tritici populations. }, number={2}, journal={PLANT DISEASE}, author={Abdelrhim, Abdelrazek and Abd-Alla, Harby M. and Abdou, El-Sayed and Ismail, Mamdoh E. and Cowger, Christina}, year={2018}, month={Feb}, pages={391–397} }
 @article{mehra_cowger_ojiambo_2017, title={A Model for Predicting Onset of Stagonospora nodorum Blotch in Winter Wheat Based on Preplanting and Weather Factors}, volume={107}, ISSN={["1943-7684"]}, DOI={10.1094/phyto-03-16-0133-r}, abstractNote={ Stagonospora nodorum blotch (SNB) caused by Parastagonospora nodorum is a serious disease of wheat worldwide. In the United States, the disease is prevalent on winter wheat in many eastern states, and its management relies mainly on fungicide application after flag leaf emergence. Although SNB can occur prior to flag leaf emergence, the relationship between the time of disease onset and yield has not been determined. Such a relationship is useful in identifying a threshold to facilitate prediction of disease onset in the field. Disease occurred in 390 of 435 disease cases that were recorded across 11 counties in North Carolina from 2012 to 2014. Using cases with disease occurrence, the effect of disease onset on yield was analyzed to identify a disease onset threshold that related time of disease onset to yield. Regression analysis showed that disease onset explained 32% of the variation in yield (P < 0.0001) and from this relationship, day of year (DOY) 102 was identified as the disease onset threshold. Below-average yield occurred in 87% of the disease cases when disease onset occurred before DOY 102 but in only 28% of those cases when onset occurred on or after DOY 102. Subsequently, binary logistic regression models were developed to predict the occurrence and onset of SNB using preplanting factors and cumulative daily infection values (cDIV) starting 1 to 3 weeks prior to DOY 102. Logistic regression showed that previous crop, latitude, and cDIV accumulated 2 weeks prior to DOY 102 (cDIV.2) were significant (P < 0.0001) predictors of disease occurrence, and wheat residue, latitude, longitude, and cDIV.2 were significant (P < 0.0001) predictors of disease onset. The disease onset model had a correct classification rate of 0.94 and specificity and sensitivity rates >0.90. Performance of the disease onset model based on the area under the receiver operating characteristic curve (AUC), κ, and the true skill statistic (TSS) was excellent, with prediction accuracy values >0.88. Similarly, internal validation of the disease onset model based on AUC, κ, and TSS indicated good performance, with accuracy values >0.88. This disease onset prediction model could serve as a useful decision support tool to guide fungicide applications to manage SNB in wheat. }, number={6}, journal={PHYTOPATHOLOGY}, publisher={Scientific Societies}, author={Mehra, L. K. and Cowger, C. and Ojiambo, P. S.}, year={2017}, month={Jun}, pages={635–644} }
 @article{wiersma_pulman_brown_cowger_olson_2017, title={Identification of Pm58 from Aegilops tauschii}, volume={130}, ISSN={["1432-2242"]}, DOI={10.1007/s00122-017-2874-8}, abstractNote={A novel powdery mildew-resistance gene, designated Pm58, was introgressed directly from Aegilops tauschii to hexaploid wheat, mapped to chromosome 2DS, and confirmed to be effective under field conditions. Selectable KASP™ markers were developed for MAS. Powdery mildew caused by Blumeria graminis (DC.) f. sp. tritici (Bgt) remains a significant threat to wheat (Triticum aestivum L.) production. The rapid breakdown of race-specific resistance to Bgt reinforces the need to identify novel sources of resistance. The D-genome species, Aegilops tauschii, is an excellent source of disease resistance that is transferrable to T. aestivum. The powdery mildew-resistant Ae. tauschii accession TA1662 (2n = 2x = DD) was crossed directly with the susceptible hard white wheat line KS05HW14 (2n = 6x = AABBDD) followed by backcrossing to develop a population of 96 BC 2 F 4  introgression lines (ILs). Genotyping-by-sequencing was used to develop a genome-wide genetic map that was anchored to the Ae. tauschii reference genome. A detached-leaf Bgt assay was used to screen BC 2 F 4:6  ILs, and resistance was found to segregate as a single locus (χ = 2.0, P value = 0.157). The resistance gene, referred to as Pm58, mapped to chromosome 2DS. Pm58 was evaluated under field conditions in replicated trials in 2015 and 2016. In both years, a single QTL spanning the Pm58 locus was identified that reduced powdery mildew severity and explained 21% of field variation (P value < 0.01). KASP™ assays were developed from closely linked GBS-SNP markers, a refined genetic map was developed, and four markers that cosegregate with Pm58 were identified. This novel source of powdery mildew-resistance and closely linked genetic markers will support efforts to develop wheat varieties with powdery mildew resistance.}, number={6}, journal={THEORETICAL AND APPLIED GENETICS}, author={Wiersma, Andrew T. and Pulman, Jane A. and Brown, Linda K. and Cowger, Christina and Olson, Eric L.}, year={2017}, month={Jun}, pages={1123–1133} }
 @article{lukaszewski_cowger_2017, title={Re-Engineering of the Pm21 Transfer from Haynaldia villosa to Bread Wheat by Induced Homoeologous Recombination}, volume={57}, ISSN={["1435-0653"]}, DOI={10.2135/cropsci2017.03.0192}, abstractNote={Blumeria graminis f. sp. tritici, the cause of powdery mildew, can generate serious grain yield losses in wheat (Triticum sp.). To expand the range of resistance genes freely available to wheat breeders, a Haynaldia villosa (L.) Schur. (syn. Dapsypyrum villosum L.)‐derived gene, Pm21, was transferred to chromosome 6AS of wheat by homoeologous recombination. The transfer showed that the genetic location of the locus was different from that suggested by an earlier transfer by irradiation. Wheat lines with two small intercalary inserts of H. villosa chromatin with Pm21 were tested with a range of powdery mildew isolates and found to be completely resistant (infection score of 0).}, number={5}, journal={CROP SCIENCE}, author={Lukaszewski, Adam J. and Cowger, Christina}, year={2017}, pages={2590–2594} }
 @article{petersen_lyerly_mckendry_islam_brown-guedira_cowger_dong_murphy_2017, title={Validation of Fusarium Head Blight Resistance QTL in US Winter Wheat}, volume={57}, ISSN={["1435-0653"]}, DOI={10.2135/cropsci2015.07.0415}, abstractNote={Fusarium head blight (FHB), primarily caused by Fusarium graminearum Schwabe [telemorph: Gibberella zeae Schw. (Petch)], can significantly reduce the grain quality of wheat (Triticum aestivum L.) due to mycotoxin contamination. Two US soft red winter wheat cultivars, Bess and NC‐Neuse, have moderate resistance to FHB. The objective of this study was to validate genomic regions associated with FHB resistance identified in previous studies involving NC‐Neuse and the cultivar Truman, a full‐sib of Bess. A total of 98 doubled haploid lines derived from the cross Bess × NC‐Neuse were evaluated in inoculated, mist‐irrigated field nurseries. The lines were evaluated for FHB incidence, severity, Fusarium‐damaged kernels, and deoxynivalenol content in seven environments between 2011 and 2014. A 3338‐cM linkage map was developed based on 4014 simple sequence repeat and single nucleotide polymorphism markers. Twelve quantitative trait loci (QTL) associated with FHB resistance were identified. NC‐Neuse alleles provided resistance at QTL on five chromosomes and Bess alleles provided resistance at QTL on five other chromosomes. Alignment of linkage maps revealed that five of these QTL were overlapping with previously identified regions. Quantitative trait loci on chromosomes 1A, 4A, and 6A identified in this study overlapped with QTL regions identified in NC‐Neuse, and QTL identified on chromosomes 2B and 3B overlapped with QTL regions identified in Truman. A preliminary test using Kompetitive Allele‐Specific polymerase chain reaction assays on recent Uniform Southern Winter Wheat Scab Nursery entries showed that the assays developed for Qfhb.nc‐2B.1 may be good candidates for use in marker‐assisted selection.}, number={1}, journal={CROP SCIENCE}, author={Petersen, Stine and Lyerly, Jeanette H. and McKendry, Anne L. and Islam, M. Sariful and Brown-Guedira, Gina and Cowger, Christina and Dong, Yanhong and Murphy, J. Paul}, year={2017}, pages={1–12} }
 @article{ben-david_parks_dinoor_kosman_wicker_keller_cowger_2016, title={Differentiation Among Blumeria graminis f. sp tritici Isolates Originating from Wild Versus Domesticated Triticum Species in Israel}, volume={106}, ISSN={["1943-7684"]}, DOI={10.1094/phyto-07-15-0177-r}, abstractNote={ Israel and its vicinity constitute a center of diversity of domesticated wheat species (Triticum aestivum and T. durum) and their sympatrically growing wild relatives, including wild emmer wheat (T. dicoccoides). We investigated differentiation within the forma specialis of their obligate powdery mildew pathogen, Blumeria graminis f. sp. tritici. A total of 61 B. graminis f. sp. tritici isolates were collected from the three host species in four geographic regions of Israel. Genetic relatedness of the isolates was characterized using both virulence patterns on 38 wheat lines (including 21 resistance gene differentials) and presumptively neutral molecular markers (simple-sequence repeats and single-nucleotide polymorphisms). All isolates were virulent on at least some genotypes of all three wheat species tested. All assays divided the B. graminis f. sp. tritici collection into two distinct groups, those from domesticated hosts and those from wild emmer wheat. One-way migration was detected from the domestic wheat B. graminis f. sp. tritici population to the wild emmer B. graminis f. sp. tritici population at a rate of five to six migrants per generation. This gene flow may help explain the overlap between the distinct domestic and wild B. graminis f. sp. tritici groups. Overall, B. graminis f. sp. tritici is significantly differentiated into wild-emmer and domesticated-wheat populations, although the results do not support the existence of a separate f. sp. dicocci. }, number={8}, journal={PHYTOPATHOLOGY}, author={Ben-David, Roi and Parks, Ryan and Dinoor, Amos and Kosman, Evsey and Wicker, Thomas and Keller, Beat and Cowger, Christina}, year={2016}, month={Aug}, pages={861–870} }
 @article{petersen_lyerly_maloney_brown-guedira_cowger_costa_dong_murphy_2016, title={Mapping of Fusarium Head Blight Resistance Quantitative Trait Loci in Winter Wheat Cultivar NC-Neuse}, volume={56}, ISSN={["1435-0653"]}, DOI={10.2135/cropsci2015.05.0312}, abstractNote={Fusarium head blight (FHB), primarily caused by Fusarium graminearum, can significantly reduce the grain quality of wheat (Triticum aestivum L.) due to mycotoxin contamination. The objective of this study was to identify quantitative trait loci (QTL) for FHB resistance in the moderately resistant soft red winter wheat cultivar NC‐Neuse. A total of 170 recombinant inbred lines (RILs) from a cross between NC‐Neuse and the susceptible cultivar AGS 2000 were evaluated in inoculated, mist‐irrigated field nurseries. The lines were evaluated for FHB incidence (INC), severity (SEV), Fusarium‐damaged kernels (FDK), and deoxynivalenol (DON) content in seven environments between 2011 and 2014. A 3,419 cM linkage map was developed based on 1839 simple sequence repeat (SSR), diversity array technology (DArT), and single nucleotide polymorphism (SNP) markers. Seven FHB resistance QTL on chromosomes 1A, 1B, 1D, 2A, 4A, 5B, and 6A were mapped. The QTL alleles conferring resistance on 1A, 1B, 2A, 4A, and 6A originated from NC‐Neuse, while the alleles associated with resistance on 1D and 5B originated from AGS 2000. Quantitative trait loci effects ranged from 9 to 12% for INC, from 6 to 11% for SEV, from 8 to 20% for FDK, and from 6 to 18% for DON. The QTL on 5B co‐localized with the Vrn‐B1 locus. Kompetitive Allele‐Specific PCR (KASP) assays were developed for each NC‐Neuse QTL region. A preliminary test using these assays on recent Uniform Southern Winter Wheat Nursery (USWWN) entries indicated Qfhb.nc‐1A, Qfhb.nc‐1B, and Qfhb.nc‐6A as likely the best candidates for use in marker‐assisted selection.}, number={4}, journal={CROP SCIENCE}, author={Petersen, Stine and Lyerly, Jeanette H. and Maloney, Peter V. and Brown-Guedira, Gina and Cowger, Christina and Costa, Jose M. and Dong, Yanhong and Murphy, J. Paul}, year={2016}, pages={1473–1483} }
 @article{cowger_weisz_arellano_murphy_2016, title={Profitability of Integrated Management of Fusarium Head Blight in North Carolina Winter Wheat}, volume={106}, ISSN={["1943-7684"]}, DOI={10.1094/phyto-10-15-0263-r}, abstractNote={ Fusarium head blight (FHB) is one of the most difficult small-grain diseases to manage, due to the partial effectiveness of management techniques and the narrow window of time in which to apply fungicides profitably. The most effective management approach is to integrate cultivar resistance with FHB-specific fungicide applications; yet, when forecasted risk is intermediate, it is often unclear whether such an application will be profitable. To model the profitability of FHB management under varying conditions, we conducted a 2-year split-plot field experiment having as main plots high-yielding soft red winter wheat cultivars, four moderately resistant (MR) and three susceptible (S) to FHB. Subplots were sprayed at flowering with Prosaro or Caramba, or left untreated. The experiment was planted in seven North Carolina environments (location–year combinations); three were irrigated to promote FHB development and four were not irrigated. Response variables were yield, test weight, disease incidence, disease severity, deoxynivalenol (DON), Fusarium-damaged kernels, and percent infected kernels. Partial profits were compared in two ways: first, across low-, medium-, or high-DON environments; and second, across environment–cultivar combinations divided by risk forecast into “do spray” and “do not spray” categories. After surveying DON and test weight dockage among 21 North Carolina wheat purchasers, three typical market scenarios were used for modeling profitability: feed-wheat, flexible (feed or flour), and the flour market. A major finding was that, on average, MR cultivars were at least as profitable as S cultivars, regardless of epidemic severity or market. Fungicides were profitable in the feed-grain and flexible markets when DON was high, with MR cultivars in the flexible or flour markets when DON was intermediate, and on S cultivars aimed at the flexible market. The flour market was only profitable when FHB was present if DON levels were intermediate and cultivar resistance was combined with a fungicide. It proved impossible to use the risk forecast to predict profitability of fungicide application. Overall, the results indicated that cultivar resistance to FHB was important for profitability, an FHB-targeted fungicide expanded market options when risk was moderate or high, and the efficacy of fungicide decision-making is reduced by factors that limit the accuracy of risk forecasts. }, number={8}, journal={PHYTOPATHOLOGY}, author={Cowger, Christina and Weisz, Randy and Arellano, Consuelo and Murphy, Paul}, year={2016}, month={Aug}, pages={814–823} }
 @article{cowger_parks_kosman_2016, title={Structure and Migration in US Blumeria graminis f. sp tritici Populations}, volume={106}, ISSN={["1943-7684"]}, DOI={10.1094/phyto-03-15-0066-r}, abstractNote={ While wheat powdery mildew occurs throughout the south-central and eastern United States, epidemics are especially damaging in the Mid-Atlantic states. The structure of the U.S. Blumeria graminis f. sp. tritici population was assessed based on a sample of 238 single-spored isolates. The isolates were collected from 16 locations in 12 states (18 site-years) as chasmothecial samples in 2003 or 2005, or as conidial samples in 2007 or 2010. DNA was evaluated using nine single nucleotide polymorphism (SNP) markers in four housekeeping genes, and 10 simple sequence repeat (SSR) markers. The SSR markers were variably polymorphic, with allele numbers ranging from 3 to 39 per locus. Genotypic diversity was high (210 haplotypes) and in eight of the site-years, every isolate had a different SSR genotype. SNP haplotypic diversity was lower; although 15 haplotypes were identified, the majority of isolates possessed one of two haplotypes. The chasmothecial samples showed no evidence of linkage disequilibrium (P = 0.36), while the conidial samples did (P = 0.001), but the two groups had nearly identical mean levels of genetic diversity, which was moderate. There was a weakly positive relationship between genetic distance and geographic distance (R2 = 0.25, P = 0.001), indicating modest isolation by distance. Most locations in the Mid-Atlantic and Great Lakes regions clustered together genetically, while Southeast locations formed a distinct but adjacent cluster; all of these were genetically separated from Southern Plains locations and an intermediate location in Kentucky. One-way migration was detected at a rate of approximately five individuals per generation from populations west of the Appalachian Mountains to those to the east, despite the fact that the Atlantic states experience more frequent and damaging wheat mildew epidemics. Overall, the evidence argues for a large-scale mosaic of overlapping populations that re-establish themselves from local sources, rather than continental-scale extinction and re-establishment, and a low rate of long-distance dispersal roughly from west to east, consistent with prevailing wind directions. }, number={3}, journal={PHYTOPATHOLOGY}, author={Cowger, Christina and Parks, Ryan and Kosman, Evsey}, year={2016}, month={Mar}, pages={295–304} }
 @article{kelly_proctor_belzile_chulze_clear_cowger_elmer_lee_obanor_waalwijk_et al._2016, title={The geographic distribution and complex evolutionary history of the NX-2 trichothecene chemotype from Fusarium graminearum}, volume={95}, ISSN={["1096-0937"]}, DOI={10.1016/j.fgb.2016.08.003}, abstractNote={Fusarium graminearum and 21 related species comprising the F. sambucinum species complex lineage 1 (FSAMSC-1) are the most important Fusarium Head Blight pathogens of cereal crops world-wide. FSAMSC-1 species typically produce type B trichothecenes. However, some F. graminearum strains were recently found to produce a novel type A trichothecene (NX-2) resulting from functional variation in the trichothecene biosynthetic enzyme Tri1. We used a PCR-RFLP assay targeting the TRI1 gene to identify the NX-2 allele among a global collection of 2515 F. graminearum. NX-2 isolates were only found in southern Canada and the northern U.S., where they were observed at low frequency (1.8%), but over a broader geographic range and set of cereal hosts than previously recognized. Phylogenetic analyses of TRI1 and adjacent genes produced gene trees that were incongruent with the history of species divergence within FSAMSC-1, indicating trans-species evolution of ancestral polymorphism. In addition, placement of NX-2 strains in the TRI1 gene tree was influenced by the accumulation of nonsynonymous substitutions associated with the evolution of the NX-2 chemotype, and a significant (P<0.001) change in selection pressure was observed along the NX-2 branch (ω=1.16) in comparison to other branches (ω=0.17) in the TRI1 phylogeny. Parameter estimates were consistent with positive selection for specific amino-acid changes during the evolution of NX-2, but direct tests of positive selection were not significant. Phylogenetic analyses of fourfold degenerate sites and intron sequences in TRI1 indicated the NX-2 chemotype had a single evolutionary origin and evolved recently from a type B ancestor. Our results indicate the NX-2 chemotype may be indigenous, and possibly endemic, to southern Canada and the northern U.S. In addition, we demonstrate that the evolution of TRI1 within FSAMSC-1 has been complex, with evidence of trans-species evolution and chemotype-specific shifts in selective constraint.}, journal={FUNGAL GENETICS AND BIOLOGY}, author={Kelly, Amy and Proctor, Robert H. and Belzile, Francois and Chulze, Sofia N. and Clear, Randall M. and Cowger, Christina and Elmer, Wade and Lee, Theresa and Obanor, Friday and Waalwijk, Cees and et al.}, year={2016}, month={Oct}, pages={39–48} }
 @article{petersen_lyerly_worthington_parks_cowger_marshall_brown-guedira_murphy_2015, title={Mapping of powdery mildew resistance gene Pm53 introgressed from Aegilops speltoides into soft red winter wheat}, volume={128}, ISSN={["1432-2242"]}, DOI={10.1007/s00122-014-2430-8}, abstractNote={A powdery mildew resistance gene was introgressed from Aegilops speltoides into winter wheat and mapped to chromosome 5BL. Closely linked markers will permit marker-assisted selection for the resistance gene. Powdery mildew of wheat (Triticum aestivum L.) is a major fungal disease in many areas of the world, caused by Blumeria graminis f. sp. tritici (Bgt). Host plant resistance is the preferred form of disease prevention because it is both economical and environmentally sound. Identification of new resistance sources and closely linked markers enable breeders to utilize these new sources in marker-assisted selection as well as in gene pyramiding. Aegilops speltoides (2n = 2x = 14, genome SS), has been a valuable disease resistance donor. The powdery mildew resistant wheat germplasm line NC09BGTS16 (NC-S16) was developed by backcrossing an Ae. speltoides accession, TAU829, to the susceptible soft red winter wheat cultivar 'Saluda'. NC-S16 was crossed to the susceptible cultivar 'Coker 68-15' to develop F2:3 families for gene mapping. Greenhouse and field evaluations of these F2:3 families indicated that a single gene, designated Pm53, conferred resistance to powdery mildew. Bulked segregant analysis showed that multiple simple sequence repeat (SSR) and single nucleotide polymorphism (SNP) markers specific to chromosome 5BL segregated with the resistance gene. The gene was flanked by markers Xgwm499, Xwmc759, IWA6024 (0.7 cM proximal) and IWA2454 (1.8 cM distal). Pm36, derived from a different wild wheat relative (T. turgidum var. dicoccoides), had previously been mapped to chromosome 5BL in a durum wheat line. Detached leaf tests revealed that NC-S16 and a genotype carrying Pm36 differed in their responses to each of three Bgt isolates. Pm53 therefore appears to be a new source of powdery mildew resistance.}, number={2}, journal={THEORETICAL AND APPLIED GENETICS}, author={Petersen, Stine and Lyerly, Jeanette H. and Worthington, Margaret L. and Parks, Wesley R. and Cowger, Christina and Marshall, David S. and Brown-Guedira, Gina and Murphy, J. Paul}, year={2015}, month={Feb}, pages={303–312} }
 @article{hao_parks_cowger_chen_wang_bland_murphy_guedira_brown-guedira_johnson_et al._2015, title={Molecular characterization of a new powdery mildew resistance gene Pm54 in soft red winter wheat}, volume={128}, ISSN={["1432-2242"]}, DOI={10.1007/s00122-014-2445-1}, abstractNote={A new powdery mildew resistance gene Pm54 was identified on chromosome 6BL in soft red winter wheat. Powdery mildew is causing increasing damage to wheat production in the southeastern USA. To combat the disease, a continuing need exists to discover new genes for powdery mildew resistance and to incorporate those genes into breeding programs. Pioneer(®) variety 26R61 (shortened as 26R61) and AGS 2000 have been used as checks in the Uniform Southern Soft Red Winter Wheat Nursery for a decade, and both have provided good resistance across regions during that time. In the present study, a genetic analysis of mildew resistance was conducted on a RIL population developed from a cross of 26R61 and AGS 2000. Phenotypic evaluation was conducted in the field at Plains, GA, and Raleigh, NC, in 2012 and 2013, a total of four environments. Three quantitative trait loci (QTL) with major effect were consistently detected on wheat chromosomes 2BL, 4A and 6BL. The 2BL QTL contributed by 26R61 was different from Pm6, a widely used gene in the southeastern USA. The other two QTL were identified from AGS 2000. The 6BL QTL was subsequently characterized as a simple Mendelian factor when the population was inoculated with a single Blumeria graminis f. sp. tritici (Bgt) isolate in controlled environments. Since there is no known powdery mildew resistance gene (Pm) on this particular location of common wheat, the gene was designated Pm54. The closely linked marker Xbarc134 was highly polymorphic in a set of mildew differentials, indicating that the marker should be useful for pyramiding Pm54 with other Pm genes by marker-assisted selection.}, number={3}, journal={THEORETICAL AND APPLIED GENETICS}, author={Hao, Y. F. and Parks, R. and Cowger, C. and Chen, Z. B. and Wang, Y. Y. and Bland, D. and Murphy, J. P. and Guedira, M. and Brown-Guedira, Gina and Johnson, J. and et al.}, year={2015}, month={Mar}, pages={465–476} }
 @article{mehra_cowger_weisz_ojiambo_2015, title={Quantifying the effects of wheat residue on severity of Stagonospora nodorum blotch and yield in winter wheat}, volume={105}, DOI={10.1094/phyto-03-15-0080-r}, abstractNote={ Stagonospora nodorum blotch (SNB), caused by the fungus Parastagonospora nodorum, is a major disease of wheat (Triticum aestivum). Residue from a previously infected wheat crop can be an important source of initial inoculum, but the effects of infected residue on disease severity and yield have not previously been quantified. Experiments were conducted in Raleigh and Salisbury, North Carolina, in 2012, 2013, and 2014 using the moderately susceptible winter wheat cultivar DG Shirley. In 2014, the highly susceptible cultivar DG 9012 was added to the experiment and the study was conducted at an additional site in Tyner, North Carolina. Four (2012) or six (2013 and 2014) wheat residue treatments were applied in the field in a randomized complete block design with five replicates. Treatments in 2012 were 0, 30, 60, and 90% residue coverage of the soil surface, while 10 and 20% residue treatments were added in 2013 and 2014. Across site-years, disease severity ranged from 0 to 50% and increased nonlinearly (P < 0.05) as residue level increased, with a rapid rise to an upper limit and showing little change in severity above 20 to 30% soil surface coverage. Residue coverage had a significant (P < 0.05) effect on disease severity in all site-years. The effect of residue coverage on yield was only significant (P < 0.05) for DG Shirley at Raleigh and Salisbury in 2012 and for DG 9012 at Salisbury in 2014. Similarly, residue coverage significantly (P < 0.05) affected thousand-kernel weight only of DG 9012 in 2014 at Raleigh and Salisbury. Our results showed that when wheat residue was sparse, small additions to residue density produced greater increases in SNB than when residue was abundant. SNB only led to effects on yield and test weight in the most disease-conducive environments, suggesting that the economic threshold for the disease may be higher than previously assumed and warrants review. }, number={11}, journal={Phytopathology}, publisher={Scientific Societies}, author={Mehra, L. K. and Cowger, Christina and Weisz, R. and Ojiambo, Peter}, year={2015}, pages={1417–1426} }
 @article{bertucci_brown-guedira_murphy_cowger_2014, title={Genes Conferring Sensitivity to Stagonospora nodorum Necrotrophic Effectors in Stagonospora Nodorum Blotch-Susceptible US Wheat Cultivars}, volume={98}, ISSN={["1943-7692"]}, DOI={10.1094/pdis-08-13-0820-re}, abstractNote={ Stagonospora nodorum is a necrotrophic fungal pathogen that causes Stagonospora nodorum blotch (SNB), a yield- and quality-reducing disease of wheat. S. nodorum produces a set of necrotrophic effectors (NEs) that interact with the products of host sensitivity genes to cause cell death and increased susceptibility to disease. The focus of this study was determination of NE sensitivity among 25 winter wheat cultivars, many of them from the southeastern United States, that are susceptible to SNB, as well as the moderately resistant ‘NC-Neuse’. Thirty-three isolates of S. nodorum previously collected from seven southeastern U.S. states were cultured for NE production, and the culture filtrates were used in an infiltration bioassay. Control strains of Pichia pastoris that expressed SnToxA, SnTox1, or SnTox3 were also used. All SNB-susceptible cultivars were sensitive to at least one NE, while NC-Neuse was insensitive to all NEs tested. Among the sensitive lines, 32% contained sensitivity gene Tsn1 and 64% contained sensitivity gene Snn3. None were sensitive to SnTox1. Additionally, 10 molecular markers for sensitivity genes Tsn1, Snn1, Snn2, and Snn3 were evaluated for diagnostic potential. Only the marker Xfcp623 for Tsn1 was diagnostic, and it was in perfect agreement with the results of the infiltration bioassays. The results illuminate which NE sensitivity genes may be of concern in breeding for resistance to SNB in the southeastern United States. }, number={6}, journal={PLANT DISEASE}, author={Bertucci, Matthew and Brown-Guedira, Gina and Murphy, J. Paul and Cowger, Christina}, year={2014}, month={Jun}, pages={746–753} }
 @article{cowger_arellano_2013, title={Fusarium graminearum Infection and Deoxynivalenol Concentrations During Development of Wheat Spikes}, volume={103}, ISSN={["1943-7684"]}, DOI={10.1094/phyto-03-12-0054-r}, abstractNote={ Fusarium head blight (FHB) affects whole spikes of small grain plants, yet little is known about how FHB develops following infection, or about the concentration or progression of the mycotoxin deoxynivalenol (DON) in non-grain spike tissues. Fusarium mycotoxin levels in whole small-grain spikes are of concern to producers of whole-crop silage, as well as users of straw containing chaff for animal bedding or winter livestock rations. A 2-year field experiment was performed in Kinston, NC to reveal the time course of FHB development. Eight winter wheat cultivars with varying levels of FHB resistance were used in the 2006 experiment, and four of them were used in 2007. Plots were spray-inoculated with Fusarium graminearum macroconidia at mid-anthesis. Four durations of post-anthesis mist were applied: 0, 10, 20, or 30 days. Spike samples were collected and bulked by plot at 15, 25, 35, 45, 55, and 65 days after anthesis (daa); samples were separated into grain, glume, and rachis fractions. Increasing durations of post-anthesis moisture elevated grain DON and reduced the effect of cultivar on DON, presumably by affecting the expression of resistance, in all spike tissues. Fusarium-damaged kernels increased from early kernel-hard to harvest-ripe in both years. Percent infected kernels increased from medium-milk to harvest-ripe. During grainfill, DON concentrations declined in grain but increased in rachises and glumes, peaking at early kernel-hard, before declining. Higher mean and maximum DON levels were observed in rachises and glumes than in grain. Estimated whole-spike DON peaked at early kernel-hard. In a high-FHB year, whole-plant harvest for forage should be conducted as early as possible. Straw that may be consumed by livestock could contain significant amounts of DON in chaff, and DON can be minimized if straw is sourced from low-symptom crops. Cultivar FHB resistance ratings and disease data should be useful in predicting whole-spike DON levels. Overall, associations between grain DON levels in harvest-ripe and prior samples were stronger the later the prior samples were collected, suggesting limits to the possibility of predicting harvest-ripe grain DON from earlier levels. }, number={5}, journal={PHYTOPATHOLOGY}, author={Cowger, Christina and Arellano, Consuelo}, year={2013}, month={May}, pages={460–471} }
 @article{crook_friesen_liu_ojiambo_cowger_2012, title={Novel Necrotrophic Effectors from Stagonospora nodorum and Corresponding Host Sensitivities in Winter Wheat Germplasm in the Southeastern United States}, volume={102}, ISSN={["1943-7684"]}, url={http://europepmc.org/abstract/med/22494247}, DOI={10.1094/phyto-08-11-0238}, abstractNote={ Stagonospora nodorum blotch (SNB), caused by the necrotrophic fungus Stagonospora nodorum (teleomorph: Phaeosphaeria nodorum), is among the most common diseases of winter wheat in the United States. New opportunities in resistance breeding have arisen from the recent discovery of several necrotrophic effectors (NEs, also known as host-selective toxins) produced by S. nodorum, along with their corresponding host sensitivity (Snn) genes. Thirty-nine isolates of S. nodorum collected from wheat debris or grain from seven states in the southeastern United States were used to investigate the production of NEs in the region. Twenty-nine cultivars with varying levels of resistance to SNB, representing 10 eastern-U.S. breeding programs, were infiltrated with culture filtrates from the S. nodorum isolates in a randomized complete block design. Three single-NE Pichia pastoris controls, two S. nodorum isolate controls, and six Snn-differential wheat controls were also used. Cultivar–isolate interactions were visually evaluated for sensitivity at 7 days after infiltration. Production of NEs was detected in isolates originating in each sampled state except Maryland. Of the 39 isolates, 17 produced NEs different from those previously characterized in the upper Great Plains region. These novel NEs likely correspond to unidentified Snn genes in Southeastern wheat cultivars, because NEs are thought to arise under selection pressure from genes for resistance to biotrophic pathogens of wheat cultivars that differ by geographic region. Only 3, 0, and 23% of the 39 isolates produced SnToxA, SnTox1, and SnTox3, respectively, by the culture-filtrate test. A Southern dot-blot test showed that 15, 74, and 39% of the isolates carried the genes for those NEs, respectively; those percentages were lower than those found previously in larger international samples. Only two cultivars appeared to contain known Snn genes, although half of the cultivars displayed sensitivity to culture filtrates containing unknown NEs. Effector sensitivity was more frequent in SNB-susceptible cultivars than in moderately resistant (MR) cultivars (P = 0.008), although some susceptible cultivars did not exhibit sensitivity to NEs produced by isolates in this study and some MR cultivars were sensitive to NEs of multiple isolates. Our results suggest that NE sensitivities influence but may not be the only determinant of cultivar resistance to S. nodorum. Specific knowledge of NE and Snn gene frequencies in this region can be used by wheat breeding programs to improve SNB resistance. }, number={5}, journal={PHYTOPATHOLOGY}, author={Crook, A. D. and Friesen, T. L. and Liu, Z. H. and Ojiambo, P. S. and Cowger, C.}, year={2012}, month={May}, pages={498–505} }
 @article{zeatfoss_cowger_ojiambo_2011, title={A Degree-Day Model for the Latent Period of Stagonospora nodorum Blotch in Winter Wheat}, volume={95}, ISSN={["0191-2917"]}, DOI={10.1094/pdis-09-10-0651}, abstractNote={ Stagonospora nodorum blotch (SNB), which is caused by Stagonospora nodorum, occurs frequently in the southeastern United States, and severe epidemics can lead to substantial yield losses. To develop a model for the progress of SNB based on the effects of temperature on the latent period of the pathogen, batches of two winter wheat cultivars, AGS 2000 and USG 3209, were inoculated with S. nodorum at weekly intervals for 16 weeks. After 72 h of incubation, inoculated plants were exposed to outdoor conditions where temperatures ranged from –6.6 to 35.8°C, with a mean batch temperature ranging from 9.7 to 24.7°C. Latent period, expressed as time from inoculation until the first visible lesions with pycnidia, ranged from 13 to 34 days. The relationship between the inverse of the latent period and mean temperature was best described by a linear model, and the estimated thermal time required for the completion of the latent period was 384.6 degree-days. A shifted cumulative gamma distribution model with a base temperature of 0.5°C significantly (P < 0.0001) described the relationship between increasing number of lesions with pycnidia and accumulated thermal time. When latent period was defined as time to 50% of the maximum number of lesions with pycnidia (L50), the model estimated L50 as 336 and 326 degree-days above 0.5°C for AGS 2000 and USG 3209, respectively. The relationship between 1/L50 and mean temperature was also best described using a linear model (r2 = 0.93, P < 0.001). This study provides data that link disease progress with wheat growth, which facilitates accurate identification of thresholds for timing of fungicide applications. }, number={5}, journal={PLANT DISEASE}, publisher={Scientific Societies}, author={Zeatfoss, A. D. and Cowger, C. and Ojiambo, P. S.}, year={2011}, month={May}, pages={561–567} }
 @article{agata_alasaad_almeida-val_alvarez-dios_barbisan_beadell_beltran_benitez_bino_bleay_et al._2011, title={Permanent genetic resources added to molecular ecology resources database 1 December 2010-31 January 2011}, volume={11}, number={3}, journal={Molecular Ecology Resources}, author={Agata, K. and Alasaad, S. and Almeida-Val, V. M. F. and Alvarez-Dios, J. A. and Barbisan, F. and Beadell, J. S. and Beltran, J. F. and Benitez, M. and Bino, G. and Bleay, C. and et al.}, year={2011}, pages={586–589} }
 @article{mcintosh_zhang_cowger_parks_lagudah_hoxha_2011, title={Rye-derived powdery mildew resistance gene Pm8 in wheat is suppressed by the Pm3 locus}, volume={123}, ISSN={["1432-2242"]}, DOI={10.1007/s00122-011-1589-5}, abstractNote={Genetic suppression of disease resistance is occasionally observed in hexaploid wheat or in its interspecific crosses. The phenotypic effects of genes moved to wheat from relatives with lower ploidy are often smaller than in the original sources, suggesting the presence of modifiers or partial inhibitors in wheat, especially dilution effects caused by possible variation at orthologous loci. However, there is little current understanding of the underlying genetics of suppression. The discovery of suppression in some wheat genotypes of the cereal rye chromosome 1RS-derived gene Pm8 for powdery mildew resistance offered an opportunity for analysis. A single gene for suppression was identified at or near the closely linked storage protein genes Gli-A1 and Glu-A3, which are also closely associated with the Pm3 locus on chromosome 1AS. The Pm3 locus is a complex of expressed alleles and pseudogenes embedded among Glu-A3 repeats. In the current report, we explain why earlier work indicated that the mildew suppressor was closely associated with specific Gli-A1 and Glu-A3 alleles, and predict that suppression of Pm8 involves translated gene products from the Pm3 locus.}, number={3}, journal={THEORETICAL AND APPLIED GENETICS}, author={McIntosh, Robert A. and Zhang, Peng and Cowger, Christina and Parks, Ryan and Lagudah, Evans S. and Hoxha, Sami}, year={2011}, month={Aug}, pages={359–367} }
 @article{schmale_wood-jones_cowger_bergstrom_arellano_2011, title={Trichothecene genotypes of Gibberella zeae from winter wheat fields in the eastern USA}, volume={60}, ISSN={["1365-3059"]}, DOI={10.1111/j.1365-3059.2011.02443.x}, abstractNote={Fusarium head blight (FHB), caused principally by Gibberella zeae (Fusarium graminearum), is a devastating disease of small grains such as wheat and barley worldwide. Grain infected with G. zeae may be contaminated with trichothecene mycotoxins such as deoxynivalenol (DON) and nivalenol (NIV). Strains of G. zeae that produce DON may also produce acetylated derivatives of DON: 3‐acetyl‐DON (3‐ADON) and 15‐acetyl‐DON (15‐ADON). Gradients (clines) of 3‐ADON genotypes in Canada have raised questions about the distribution of G. zeae trichothecene genotypes in wheat fields in the eastern USA. Tri3 and Tri12 genotypes were evaluated in 998 isolates of G. zeae collected from 39 winter wheat fields in New York (NY), Pennsylvania (PA), Maryland (MD), Virginia (VA), Kentucky (KY) and North Carolina (NC). Ninety‐two percent (919/998) of the isolates were 15‐ADON, 7% (69/998) were 3‐ADON, and 1% (10/998) was NIV. A phylogenetic analysis based on portions of three genes (PHO, RED and URA) from 23 isolates revealed two species of Fusarium (F. graminearum sensu stricto and one isolate of F. cerealis (synonym F. crookwellense)). An increasing trend of 3‐ADON genotypes was observed from NC (south) to NY (north). Punctuated episodes of atmospheric transport may favour a higher frequency of 3‐ADON genotypes in the northeastern USA, near Canada, compared with the mid‐Atlantic states. Discoveries of the NIV genotype in NY and NC indicate the need for more intensive sampling in the surrounding regions.}, number={5}, journal={PLANT PATHOLOGY}, author={Schmale, D. G. and Wood-Jones, A. K. and Cowger, C. and Bergstrom, G. C. and Arellano, C.}, year={2011}, month={Oct}, pages={909–917} }
 @article{cowger_weisz_anderson_horton_2010, title={Maize Debris Increases Barley Yellow Dwarf Virus Severity in North Carolina Winter Wheat}, volume={102}, ISSN={["0002-1962"]}, DOI={10.2134/agronj2009.0357}, abstractNote={In the eastern United States, wheat (Triticum aestivum L.) is often planted with minimal or no tillage into maize (Zea mays L.) residues. We conducted a field experiment in the North Carolina Piedmont to compare the effects of three maize residue treatments (unchopped, chopped, and removed) on Fusarium head blight (FHB) in two winter wheat cultivars. While FHB levels were too low for meaningful comparisons, severe epidemics of barley/cereal yellow dwarf virus (YDV) did develop in 2 yr out of 3. In those 2 yr, YDV symptoms of discoloration and stunting were greater (P ≤ 0.001), and yield was lower (P ≤ 0.01), in plots with maize residue than in plots without maize residue. In the third year, when planting was late because of a severe fall drought, no YDV epidemic developed, and there were no differences in wheat yield due to maize residue treatment (P = 0.25). In the first 2 yr, leaf samples from all plots were assayed for viruses using a multiplexed reverse transcription polymerase chain reaction (RT‐PCR) method. The most common YDV serotypes were MAV, PAV, and RPV, which were each detected in at least 46 and 74% of samples in the 2 yr, respectively. Our finding of greater YDV severity in association with surface residue is consistent with the reported aphid preference for high‐intensity yellow colors, which we hypothesize attracted aphids preferentially to residue‐covered plots in the fall. Our results support a recommendation of seed or seedling insecticide treatment when planting wheat into heavy unincorporated maize residue in the U.S. Piedmont.}, number={2}, journal={AGRONOMY JOURNAL}, author={Cowger, Christina and Weisz, Randy and Anderson, Joseph M. and Horton, J. Ray}, year={2010}, pages={688–695} }
 @article{maxwell_lyerly_srnic_parks_cowger_marshall_brown-guedira_murphy_2010, title={MlAB10: A triticum turgidum subsp dicoccoides derived powdery mildew resistance gene identified in common wheat}, volume={50}, number={6}, journal={Crop Science}, author={Maxwell, J. J. and Lyerly, J. H. and Srnic, G. and Parks, R. and Cowger, C. and Marshall, D. and Brown-Guedira, G. and Murphy, J. P.}, year={2010}, pages={2261–2267} }
 @article{cowger_arrellano_2010, title={Plump Kernels with High Deoxynivalenol Linked to Late Gibberella zeae Infection and Marginal Disease Conditions in Winter Wheat}, volume={100}, ISSN={["0031-949X"]}, DOI={10.1094/phyto-100-7-0719}, abstractNote={ Deoxynivalenol (DON) concentrations in mature wheat grain are usually correlated with symptoms produced by Gibberella zeae infection. However, there have been numerous observations of unacceptably high DON in asymptomatic crops, which can lead to lower-than-expected milling reductions in DON. We conducted a field experiment with winter wheat to examine the effect of infection timing and postanthesis moisture on grain quality and DON accumulation. Seven to eight soft red winter wheat cultivars were grown in three successive years in a misted nursery in Kinston, NC. Spikes were randomly selected for individual spray inoculation at 0, 10, or 20 days after anthesis (daa). Starting at anthesis, plots were subjected to 0, 10, 20, or 30 days of mist. Inoculated spikes and noninoculated controls were collected at harvest-ripeness, and the threshed grain was assayed for Fusarium-damaged kernels (FDK) and DON. In 2 of 3 years, percentages of FDK were significantly lower from 10-daa infections than from those at 0 daa, although DON concentrations were the same at the two inoculation timings in 2 of the 3 years. Those results indicate that the period of maximum susceptibility to wheat spike infections by G. zeae is close to or slightly less than 10 daa in North Carolina. In 2 of 3 years, FDK–DON correlation was greater for 0- and 10-daa inoculations and for 0- to 20-daa misted treatments than for the later-inoculated or longer-misted treatments, respectively. The percentage of “low-FDK, high DON” (LFHD) observations (defined as FDK ≤ 4.0%, DON ≥ 2 μg g–1) was higher in 2007 than in 2005 or 2006 (41, 14, and 18%, respectively). In both 2006 and 2007, high percentages of LFHD observations (≥60%) occurred under marginal disease conditions involving late infection. We conclude that late infection is an important factor leading to LFHD grain. Periods of rain soon after anthesis likely favor the low-symptom, high-DON scenario, and conditions that create greater within-crop variability of anthesis timing may also be important. }, number={7}, journal={PHYTOPATHOLOGY}, author={Cowger, Christina and Arrellano, Consuelo}, year={2010}, month={Jul}, pages={719–728} }
 @article{costa_bockelman_brown-guedira_cambron_chen_cooper_cowger_dong_grybauskas_jin_et al._2010, title={Registration of the Soft Red Winter Wheat Germplasm MD01W233-06-1 Resistant to Fusarium Head Blight}, volume={4}, ISSN={["1936-5209"]}, DOI={10.3198/jpr2010.01.0034crg}, abstractNote={Fusarium head blight (FHB) [caused by Fusarium graminearum Schwabe; telomorph Gibberella zeae (Schwein.) Petch] is a major disease of winter wheat (Triticum aestivum L.) in the US mid‐Atlantic region. The objective of this research was to derive soft red winter wheat (SRWW) germplasm with enhanced FHB resistance for this region. MD01W233–06–1 (Reg. No. GP‐857, PI No. 658682) is a soft red winter wheat (SRWW) (Triticum aestivum L.) germplasm line developed at the University of Maryland and released by the Maryland Agricultural Experiment Station in 2009. MD01W233–06–1 was selected from the cross ‘McCormick’/‘Choptank’ made in 2001. McCormick and Choptank are SRWW cultivars adapted to the US mid‐Atlantic region. MD01W233–06–1 was selected as an F3:5 line selection in Queenstown, MD in June 2006. MD01W233–06–1 has type II resistance to FHB that is different from that of ‘Sumai 3’. Additionally, it has resistance to the Ug99 race of stem rust. These characteristics make this line a valuable contribution for breeding for enhanced FHB resistance in the US mid‐Atlantic.}, number={3}, journal={JOURNAL OF PLANT REGISTRATIONS}, author={Costa, Jose M. and Bockelman, Harold E. and Brown-Guedira, Gina and Cambron, Sue E. and Chen, Xianming and Cooper, Aaron and Cowger, Christina and Dong, Yanghong and Grybauskas, Arvydas and Jin, Yue and et al.}, year={2010}, month={Sep}, pages={255–260} }
 @article{mundt_sackett_wallace_cowger_dudley_2009, title={Aerial Dispersal and Multiple-Scale Spread of Epidemic Disease}, volume={6}, ISSN={["1612-9210"]}, DOI={10.1007/s10393-009-0251-z}, abstractNote={Disease spread has traditionally been described as a traveling wave of constant velocity. However, aerially dispersed pathogens capable of long-distance dispersal often have dispersal gradients with extended tails that could result in acceleration of the epidemic front. We evaluated empirical data with a simple model of disease spread that incorporates logistic growth in time with an inverse power function for dispersal. The scale invariance of the power law dispersal function implies its applicability at any spatial scale; indeed, the model successfully described epidemics ranging over six orders of magnitude, from experimental field plots to continental-scale epidemics of both plant and animal diseases. The distance traveled by epidemic fronts approximately doubled per unit time, velocity increased linearly with distance (slope ~(1/2)), and the exponent of the inverse power law was approximately 2. We found that it also may be possible to scale epidemics to account for initial outbreak focus size and the frequency of susceptible hosts. These relationships improve understanding of the geographic spread of emerging diseases, and facilitate the development of methods for predicting and preventing epidemics of plants, animals, and humans caused by pathogens that are capable of long-distance dispersal.}, number={4}, journal={ECOHEALTH}, author={Mundt, Christopher C. and Sackett, Kathryn E. and Wallace, LaRae D. and Cowger, Christina and Dudley, Joseph P.}, year={2009}, month={Dec}, pages={546–552} }
 @article{cowger_parks_marshall_2009, title={Appearance of Powdery Mildew of Wheat Caused by Blumeria graminis f. sp tritici on Pm17-Bearing Cultivars in North Carolina.}, volume={93}, ISSN={["0191-2917"]}, DOI={10.1094/PDIS-93-11-1219B}, abstractNote={ Pm17 is a gene for resistance to powdery mildew caused by Blumeria graminis (DC.) E.O. Speer f. sp. tritici. The gene was first confirmed in the wheat-rye translocation cultivar Amigo (1). In Amigo, the translocation is T1AL-1RS and the 1RS arm has the gene Pm17. In the mid-Atlantic United States, at least two widely deployed soft red winter wheat (Triticum aestivum L.) cultivars, McCormick (2) and Tribute (3), possess Pm17 inherited from Amigo. Before 2009, low frequencies of mostly intermediate virulence to Pm17 were detected among isolates from research plots of highly susceptible cultivars (4), but Pm17-bearing cultivars remained immune to mildew in the field. In April 2009, moderately severe powdery mildew was observed for the first time throughout plots of McCormick, Tribute, and other cultivars in both Kinston and Raleigh, NC. At Kinston, Pm17 virulence was observed at two research sites, separated by approximately 10 km, throughout plots of Amigo, McCormick, Tribute, and the hard red winter wheat cultivar TAM 303, which also contains Pm17. In the same month, virulence to Pm17 was observed in Raleigh throughout rows and plots of Amigo and TAM 303. In Kinston and Raleigh, ratings of powdery mildew severity on the Pm17-containing cultivars were 4 or 5 on a scale of 0 to 9, with 0 being the absence of mildew pustules and 9 the most severe mildew infection. Mildew was observed on leaves of all ages. Mildewed leaves were collected from field plots of all four Pm17-bearing cultivars, and an assay to confirm Pm17 virulence was conducted in the laboratory. Mixed-isolate cultures were derived from the leaves and a detached-leaf assay was performed using Amigo, which is the standard Pm17 differential (4). All tested cultures were fully to moderately virulent on Pm17 and all were fully virulent on the susceptible control Chancellor. In the field, chasmothecia (sexual fruiting bodies) were observed on Pm17-bearing cultivars. Together with the quantitatively varying Pm17 virulence detected in the laboratory assay, this suggests that multiple strains of Pm17-virulent B. graminis f. sp. tritici may be present in the field, although that has not yet been demonstrated. Pm17 has protected wheat from powdery mildew over a substantial area in the mid-Atlantic United States. The loss of Pm17 is the most important virulence shift in the U.S. wheat powdery mildew population since Pm4a became ineffective around 2002. Isolates virulent to Pm17 can be expected to appear and multiply in wheat-producing states of the mid-Atlantic United States, including Delaware, Maryland, Virginia, North Carolina, South Carolina, and Georgia. Thus, the urgency of developing and releasing wheat cultivars with other sources of effective mildew resistance is heightened. }, number={11}, journal={PLANT DISEASE}, author={Cowger, C. and Parks, R. and Marshall, D.}, year={2009}, month={Nov}, pages={1219–1219} }
 @article{mundt_sackett_wallace_cowger_dudley_2009, title={Long-Distance Dispersal and Accelerating Waves of Disease: Empirical Relationships}, volume={173}, ISSN={["1537-5323"]}, DOI={10.1086/597220}, abstractNote={Classic approaches to modeling biological invasions predict a “traveling wave” of constant velocity determined by the invading organism’s reproductive capacity, generation time, and dispersal ability. Traveling wave models may not apply, however, for organisms that exhibit long‐distance dispersal. Here we use simple empirical relationships for accelerating waves, based on inverse power law dispersal, and apply them to diseases caused by pathogens that are wind dispersed or vectored by birds: the within‐season spread of a plant disease at spatial scales of <100 m in experimental plots, historical plant disease epidemics at the continental scale, the unexpectedly rapid spread of West Nile virus across North America, and the transcontinental spread of avian influenza strain H5N1 in Eurasia and Africa. In all cases, the position of the epidemic front advanced exponentially with time, and epidemic velocity increased linearly with distance; regression slopes varied over a relatively narrow range among data sets. Estimates of the inverse power law exponent for dispersal that would be required to attain the rates of disease spread observed in the field also varied relatively little (1.74–2.36), despite more than a fivefold range of spatial scale among the data sets.}, number={4}, journal={AMERICAN NATURALIST}, author={Mundt, Christopher C. and Sackett, Kathryn E. and Wallace, Larae D. and Cowger, Christina and Dudley, Joseph P.}, year={2009}, month={Apr}, pages={456–466} }
 @article{maxwell_lyerly_cowger_marshall_brown-guedira_murphy_2009, title={MlAG12: a Triticum timopheevii-derived powdery mildew resistance gene in common wheat on chromosome 7AL}, volume={119}, ISSN={["1432-2242"]}, DOI={10.1007/s00122-009-1150-y}, abstractNote={Wheat powdery mildew is an economically important disease in cool and humid environments. Powdery mildew causes yield losses as high as 48% through a reduction in tiller survival, kernels per head, and kernel size. Race-specific host resistance is the most consistent, environmentally friendly and, economical method of control. The wheat (Triticum aestivum L.) germplasm line NC06BGTAG12 possesses genetic resistance to powdery mildew introgressed from the AAGG tetraploid genome Triticum timopheevii subsp. armeniacum. Phenotypic evaluation of F(3) families derived from the cross NC06BGTAG12/'Jagger' and phenotypic evaluation of an F(2) population from the cross NC06BGTAG12/'Saluda' indicated that resistance to the 'Yuma' isolate of powdery mildew was controlled by a single dominant gene in NC06BGTAG12. Bulk segregant analysis (BSA) revealed simple sequence repeat (SSR) markers specific for chromosome 7AL segregating with the resistance gene. The SSR markers Xwmc273 and Xwmc346 mapped 8.3 cM distal and 6.6 cM proximal, respectively, in NC06BGTAG12/Jagger. The multiallelic Pm1 locus maps to this region of chromosome 7AL. No susceptible phenotypes were observed in an evaluation of 967 F(2) individuals in the cross NC06BGTAG12/'Axminster' (Pm1a) which indicated that the NC06BGTAG12 resistance gene was allelic or in close linkage with the Pm1 locus. A detached leaf test with ten differential powdery mildew isolates indicated the resistance in NC06BGTAG12 was different from all designated alleles at the Pm1 locus. Further linkage and allelism tests with five other temporarily designated genes in this very complex region will be required before giving a permanent designation to this gene. At this time the gene is given the temporary gene designation MlAG12.}, number={8}, journal={THEORETICAL AND APPLIED GENETICS}, author={Maxwell, Judd J. and Lyerly, Jeanette H. and Cowger, Christina and Marshall, David and Brown-Guedira, Gina and Murphy, J. Paul}, year={2009}, month={Nov}, pages={1489–1495} }
 @article{parks_carbone_murphy_cowger_2009, title={Population Genetic Analysis of an Eastern US Wheat Powdery Mildew Population Reveals Geographic Subdivision and Recent Common Ancestry with UK and Israeli Populations}, volume={99}, ISSN={["1943-7684"]}, DOI={10.1094/PHYTO-99-7-0840}, abstractNote={ The structure of the U.S. wheat powdery mildew population (Blumeria graminis f. sp. tritici) has not been previously investigated, and the global evolutionary history of B. graminis f. sp. tritici is largely unknown. After gathering 141 single-ascosporic B. graminis f. sp. tritici isolates from 10 eastern U.S. locations, 34 isolates from the United Kingdom, and 28 isolates from Israel, we analyzed pathogen population structure using presumptively neutral markers. DNA was extracted from conidia, primers for 12 “housekeeping” genes were designed, and amplicons were examined for polymorphism. Four genes were found to contain a total of 12 single-nucleotide polymorphisms in the U.S. population and were also analyzed in the U.K. and Israeli populations. In total, 25 haplotypes were inferred from the four concatenated genes, with 2 haplotypes comprising over 70% of the U.S. population. Using Hudson's tests and analysis of molecular variance, we found the wheat mildew isolates subdivided into four groups corresponding to distinct regions: the mid-Atlantic United States, the southern United States, the United Kingdom, and Israel. Genotypic diversity was greatest in samples from the United Kingdom, Israel, Virginia, and Kinston, NC. Using rarefaction, a procedure that compensates for differing sample sizes when estimating population richness and diversity, we found that cooler locations with greater conduciveness to regular powdery mildew epidemics had the greatest haplotype richness. Our results suggest that the eastern U.S. B. graminis f. sp. tritici population is young, descended recently from Old World populations with isolation and genetic drift, and is currently subdivided into northern and southern subpopulations. }, number={7}, journal={PHYTOPATHOLOGY}, author={Parks, Ryan and Carbone, Ignazio and Murphy, J. Paul and Cowger, Christina}, year={2009}, month={Jul}, pages={840–849} }
 @article{cowger_patton-ozkurt_brown-guedira_perugini_2009, title={Post-Anthesis Moisture Increased Fusarium Head Blight and Deoxynivalenol Levels in North Carolina Winter Wheat}, volume={99}, ISSN={["0031-949X"]}, DOI={10.1094/PHYTO-99-4-0320}, abstractNote={ Current models for forecasting Fusarium head blight (FHB) and deoxynivalenol (DON) levels in wheat are based on weather near anthesis, and breeding for resistance to FHB pathogens often relies on irrigation before and shortly after anthesis to encourage disease development. The effects of post-anthesis environmental conditions on FHB are poorly understood. We performed a field experiment at Kinston, NC, to explore the effects of increasing duration of post-anthesis moisture on disease incidence, disease severity, Fusarium-damaged kernels (FDK), percent infected kernels, and DON. The experiment had a split-plot design, and one trial was conducted in each of two successive years. Main plots consisted of post-anthesis mist durations of 0, 10, 20, or 30 days. Subplots were of eight cultivars in the first year and seven in the second year, two being susceptible to FHB and the remainder each with varying degrees of apparent type I and type II resistance. Plots were inoculated by spraying Fusarium graminearum macroconidia at mid-anthesis. Averaging across years and cultivars, 10 or 20 days of post-anthesis mist had the same effect (P ≥ 0.198) and were associated with an approximately fourfold increase in mean disease incidence and eightfold increase in disease severity compared with 0 days of mist (P ≤ 0.0002). In both years, mean FDK percentages at 0 and 10 days post-anthesis mist were the same and significantly lower than FDK percentages under 20 or 30 days of post-anthesis mist. Mist duration had a significant effect on percent kernels infected with Fusarium spp. as detected by a selective medium assay of 2007 samples. Averaging across all cultivars, in both years, DON levels increased significantly for 10 days compared with 0 days of mist, and increased again with 20 days of mist (P ≤ 0.04). This is the first investigation to show that extended post-flowering moisture can have a significant enhancing effect on FHB, FDK, DON, and percent infected kernels of wheat. For all disease and toxin assays, cultivar rankings were significantly noncorrelated among mist durations in at least 1 year, suggesting that FHB screening programs might rank genotypes differently under extended post-anthesis moisture than without it. Our findings also imply that accurate forecasts of DON in small grains must take account of post-anthesis weather conditions. }, number={4}, journal={PHYTOPATHOLOGY}, author={Cowger, Christina and Patton-Ozkurt, Jennifer and Brown-Guedira, Gina and Perugini, Leandro}, year={2009}, month={Apr}, pages={320–327} }
 @article{cowger_brunner_mundt_2008, title={Frequency of sexual recombination by Mycosphaerella graminicold in mild and severe epidemics}, volume={98}, ISSN={["0031-949X"]}, DOI={10.1094/PHYTO-98-7-0752}, abstractNote={ The importance of sexual recombination in determining fungal population structure cannot be inferred solely from the relative abundance of sexual and asexual spores and reproductive structures. To complement a previously reported study of proportions of Mycosphaerella graminicola ascocarps and pycnidia, we investigated the share of sexual recombinants among isolates randomly derived from the same field at the same time. Early in three successive growing seasons (those ending in 1998, 1999, and 2000), field plots of the susceptible winter wheat cultivar Stephens were inoculated with suspensions of two M. graminicola isolates that each had rare alleles at restriction fragment length polymorphism (RFLP) loci. Near harvest time, leaves were randomly sampled from the same plots, and a population of over 100 monopycnidial isolates was created for each year of the experiment. Natural populations were also sampled from noninoculated plots in the 1999 and 2000 seasons, in order to compare allele frequencies. Based on RFLP haplotypes and DNA fingerprints, isolates from the inoculated plots were categorized by both inspection and Bayesian methods as inoculant clones, recombinants, or immigrants. Inoculation in the 2000 season was delayed, and the recovery rate of inoculant types was just 1 to 2%. In 1998, a high-disease year, and 1999, a low-disease year, inoculants comprised 36 and 22 to 23% of end-of-season samples, respectively. In those 2 years, recombinants as a percentage of inoculant descendants (both sexual and asexual) were 35 and 32%, respectively. By comparison, the study of fruiting bodies had found 93 and 32% of M. graminicola fruiting bodies were ascocarps in 1998 and 1999, respectively. These findings support the hypothesis that sexual recombination makes a relatively consistent contribution to M. graminicola population structure, despite differences in epidemic severity and ascocarp proportions. }, number={7}, journal={PHYTOPATHOLOGY}, author={Cowger, C. and Brunner, P. C. and Mundt, C. C.}, year={2008}, month={Jul}, pages={752–759} }
 @article{parks_carbone_murphy_marshall_cowger_2008, title={Virulence structure of the Eastern US wheat powdery mildew population}, volume={92}, ISSN={["0191-2917"]}, DOI={10.1094/PDIS-92-7-1074}, abstractNote={ Little is known about the population structure of wheat powdery mildew in the eastern United States, and the most recent report on virulence in this population involved isolates collected in 1993–94. In the present study, wheat leaves naturally infected with powdery mildew were collected from 10 locations in the southeastern United States in 2003 and 2005 and a collection of 207 isolates was derived from single ascospores. Frequencies of virulence to 16 mildew resistance (Pm) genes were determined by inoculating the isolates individually on replicated plates of detached leaves of differential wheat lines. These virulence frequencies were used to infer local effectiveness of Pm genes, estimate virulence complexity, detect significant associations between pairs of pathogen avirulence loci, and assess whether phenotypic differences between pathogen subpopulations increased with geographic distance. In both years, virulence to Pm3a, Pm3c, Pm5a, and Pm7 was present in more than 90% of sampled isolates and virulence to Pm1a, Pm16, Pm17, and Pm25 was present in fewer than 10% of isolates. In each year, 71 to 88% of all sampled isolates possessed one of a few multilocus virulence phenotypes, although there were significant differences among locations in frequencies of virulence to individual Pm genes. Several significant associations were detected between alleles for avirulence to pairs of Pm genes. Genetic (phenotypic) distance between isolate subpopulations increased significantly (R2 = 0.40, P < 0.001) with increasing geographic separation; possible explanations include different commercial deployment of Pm genes and restricted gene flow in the pathogen population. }, number={7}, journal={PLANT DISEASE}, author={Parks, Ryan and Carbone, Ignazio and Murphy, J. Paul and Marshall, David and Cowger, Christina}, year={2008}, month={Jul}, pages={1074–1082} }
 @article{cowger_weisz_2008, title={Winter wheat blends (mixtures) produce a yield advantage in north Carolina}, volume={100}, ISSN={["1435-0645"]}, DOI={10.2134/agronj2007.0128}, abstractNote={Seed mixtures, or blends, of small grain cultivars are unknown in eastern U.S. wheat production, where numerous diseases and abiotic stresses often reduce yield and quality. In 2004–2005 and 2005–2006, a field experiment was conducted at Kinston, Plymouth, and Salisbury, NC, to compare performance of eight soft red winter wheat (Triticum aestivum L.) cultivars having a range of maturities with that of 13 blends, each consisting of equal proportions of two or three of the cultivars. The blends were composed to have complementary disease resistance traits. Disease pressure was at most moderate in any environment. Blends significantly outyielded the means of their respective components (midcomponents) in Plymouth in 2005 (P = 0.042) and across all environments (P = 0.039), with a mean overall blend advantage of 0.13 Mg ha−1. Averaged across environments, two blends significantly outyielded their midcomponents (P ≤ 0.011). Yield stability of blends exceeded that of pure cultivars by the stability variance model and principal component analysis. In general, blends did not differ significantly from midcomponents for test weight (P = 0.37), protein content (P = 0.10), hardness (P = 0.68), or falling number (sprouting tolerance, P = 0.89), but seed diameter nonuniformity of blends exceeded that of midcomponents (P = 0.0002). Wheat blends may offer a small yield advantage to North Carolina growers even in the absence of severe disease.}, number={1}, journal={AGRONOMY JOURNAL}, author={Cowger, Christina and Weisz, Randy}, year={2008}, pages={169–177} }
 @article{cowger_murphy_2007, title={Artificial inoculation of wheat for selecting resistance to Stagonospora nodorum blotch}, volume={91}, ISSN={["1943-7692"]}, DOI={10.1094/PDIS-91-5-0539}, abstractNote={ In the eastern United States, natural epidemics of Stagonospora nodorum blotch (SNB) are not consistently severe enough to facilitate substantial progress in breeding moderately resistant cultivars of soft red winter wheat. We compared three artificial inoculation methods to natural inoculum in a field experiment involving seven wheat (Triticum aestivum) cultivars with varying levels of SNB resistance. Artificial inoculation methods were: Phaeosphaeria nodorum conidia applied by atomization to three- to four-leaf wheat in early winter, P. nodorum conidia applied by atomization at boot stage in late spring, and P. nodorum-infected wheat straw applied in early winter. The experiment was conducted at Kinston and Plymouth, NC, in 2003–2004, 2004–2005, and 2005–2006, and all treatments had three replicates. Percent diseased canopy was assessed and comparisons were made using disease severity at a single date (early to soft dough stage) and area under the disease progress curve (AUDPC). The relative resistance level of cultivars was consistent across sites, years, and inoculum methods, although the rankings of moderately susceptible and susceptible cultivars were sometimes switched. On average, late spores and straw caused significantly more disease than early spores or natural inoculum (P ≤ 0.05). Biplot analysis indicated that all artificial methods had a higher mean capacity to discriminate among cultivars than did natural inoculum (P ≤ 0.05). On average, artificial inoculation increased the capacity of environments to separate wheat cultivars by SNB resistance. }, number={5}, journal={PLANT DISEASE}, author={Cowger, Christina and Murphy, J. Paul}, year={2007}, month={May}, pages={539–545} }
 @article{cowger_silva-rojas_2006, title={Frequency of Phaeosphaeria nodorum, the sexual stage of Stagronospora nodorum, on winter wheat in North Carolina}, volume={96}, ISSN={["0031-949X"]}, DOI={10.1094/PHYTO-96-0860}, abstractNote={ Ascocarps of Phaeosphaeria nodorum, which causes Stagonospora nodorum blotch (SNB) of wheat, have not been found by others in the eastern United States despite extensive searches. We sampled tissues from living wheat plants or wheat debris in Kinston, NC, each month except June from May to October 2003. Additional wheat samples were gathered in Kinston, Salisbury, and Plymouth, NC, in 2004 and 2005. For the 3 years, in all, 2,781 fruiting bodies were dissected from the wheat tissues and examined microscopically. Fruiting bodies were tallied as P. nodorum pycnidia or ascocarps, “unknown” (not containing spores, potentially P. nodorum or other fungi), or “other fungi.” In the 2003 sample, asco-carps of P. nodorum were present each month after May at a frequency of 0.8 to 5.4%, and comprised a significantly higher percentage of fruiting bodies from wheat spikes than of those from lower stems and leaves. Ascocarps also were found at frequencies <10% in some wheat debris samples from 2004 and 2005. Analysis of the nucleotide sequences of internally transcribed spacer regions of 18 genetically distinct North Carolina isolates from 2003 suggested that all were P. nodorum, not the morphologically similar P. avenaria f. sp. triticea. Neither the 18 isolates from 2003 nor a set of 77 isolates derived from 2004 Kinston leaf samples gave reason to suspect a mating-type imbalance in the larger P. nodorum population (P ≥ 0.4). We conclude that, in North Carolina, sexual reproduction plays a role in initiation of SNB epidemics and the creation of adaptively useful genetic variability, although its relative importance in structuring this population is uncertain. }, number={8}, journal={PHYTOPATHOLOGY}, author={Cowger, Christina and Silva-Rojas, Hilda Victoria}, year={2006}, month={Aug}, pages={860–866} }
 @article{cowger_sutton_2005, title={The Southeastern U.S. fusarium head blight epidemic of 2003}, ISBN={1535-1025}, DOI={10.1094/php-2005-1026-01-rs}, abstractNote={ Fusarium head blight (FHB) caused unprecedented losses to southeastern U.S. wheat producers and millers in 2003. The epidemic was documented afterward through interviews with 120 researchers, extension agents, millers, and growers. Sixty-two counties in five states were assigned an FHB impact score of 1 to 4, and 2003 yield and weather data were obtained for those counties. The relationships of yield and pre- and post-flowering weather variables to impact score were evaluated using regression and correlation analyses. Yield as a percentage of the 10-year average was negatively correlated with FHB impact (r = -0.588, P < 0.0001). FHB impact was positively correlated with hours of post-flowering rainfall (r = 0.465, 0.590, and 0.619 for 10, 20, and 30 days post-flowering, respectively; P = 0.0001), but not correlated with hours of pre-flowering rainfall (P = 0.99). While this was not a controlled study, the results suggest that pre-flowering weather may have played a less significant role than post-flowering weather, and was unlikely to have been a good predictor of FHB severity in the southeast in 2003. Using 10-year average production data, premilling economic losses were estimated for 40 counties in Maryland, Virginia, and North Carolina at over $13.6 million. Wheat production in those counties comprised just 71.7%, 45.8%, and 48.0% of the statewide totals, respectively; thus, actual 2003 FHB-related losses to growers in those states were probably much higher. Additionally, mills in the region suffered losses of several million dollars in 2003 due to increased shipping, testing, and handling costs brought on by FHB. }, journal={Plant Health Progress}, author={Cowger, Christina and Sutton, A. L.}, year={2005}, pages={1} }
 @article{cowger_wallace_mundt_2005, title={Velocity of spread of wheat stripe rust epidemics}, volume={95}, DOI={10.1094/PHYTO.95-0972}, abstractNote={ABSTRACT Controversy has long existed over whether plant disease epidemics spread with constant or with increasing velocity. We conducted largescale field experiments with wheat stripe rust at Madras and Hermiston, Oregon, where natural stripe rust epidemics were rare, to test these competing models. Data from three location-years were available for analysis. A susceptible winter wheat cultivar was planted in pure stand and also in a 1:4 or 1:1 mixture with a cultivar immune to the stripe rust race utilized in the experiments. Plots were 6.1 m wide and varied from 73 to 171 m in length. A 1.5 by 1.5-m focus was inoculated in either the center (2001) or upwind of the center (2002 and 2003) of each plot. Disease severity was evaluated weekly throughout the epidemics in each plot at the same points along a transect running upwind and downwind from the focus. Velocity of spread was calculated from the severity data and regressed separately on time and on distance from the focus. In all location-years and treatments, and at all levels of disease severity, velocity consistently increased linearly with distance, at an average rate of 0.59 m/week per m, and exponentially with time. Further, across epidemics there was a significant positive relationship between the apparent infection rate, r, and the rate of velocity increase in both space and time. These findings have important implications for plant diseases with a focal or partially focal character, and in particular for the effectiveness of ratereducing disease management strategies at different spatial scales.}, number={9}, journal={Phytopathology}, author={Cowger, Christina and Wallace, L. R. D. and Mundt, C. C.}, year={2005}, pages={972–982} }