@article{sanabria-velazquez_cubilla_flores-giubi_barua_romero-rodriguez_enciso-maldonado_thiessen_shew_2023, title={First Report of Macrophomina euphorbiicola Causing Charcoal Rot of Stevia in Paraguay}, volume={107}, ISSN={["1943-7692"]}, DOI={10.1094/PDIS-06-21-1279-PDN}, abstractNote={Stevia (Stevia rebaudiana [Bertoni] Bertoni) is a perennial plant originating in Paraguay. Stevia is primarily cultivated for the production of non-caloric sweeteners. In December 2018, wilted stevia cv. 'PC4' were recovered from two separate fields of 0.3 ha (24.66 S 56.46 W) and 0.5 ha (24.69 S 56.44 W), both with 3 years history of stevia production in San Estanislao County, San Pedro, Paraguay. The wilted plants were randomly distributed in beds covered with plastic mulch and a 30% disease incidence was recorded. Dark brown septate hyphae and microsclerotia were observed on stem bases and black necrotic roots of the wilted plants. Root and crown regions were washed, cut into 0.5 to 1.0 cm pieces, and then surface-disinfested with 0.6% NaOCl before placing them in Petri dishes containing acidified potato-dextrose-agar. Plates were incubated for one week at 25 ± 5°C under fluorescent light with a 12 h photoperiod yielding five isolates SP1PY, SP2PY, SP3PY, SP4PY and SP5PY with gray-black colonies without conidia but showing numerous microsclerotia. Twenty microsclerotia from pure cultures of five isolates were measured, with mean width 38.8 ± 4.7 µm and length 68.8 ± 15.5 µm. Fungal DNA was extracted from mycelia of five isolates for PCR amplification of the internal transcribed spacer (ITS) and translation elongation factor 1-alpha (TEF1-α) using ITS4/ITS5 and EF1-728F/EF-2 primers (Machado et al. 2019). The resultant amplicons were sequenced at Eton Bioscience (Research Triangle Park, NC) and deposited in the NCBI GenBank database (ITS: MT645815, OM956150, OM956151, OM956152, OM956153; and TEF1-α: MT659121, OM959505, OM959506, OM959507, OM959508). Sequences were aligned with several isolates of Macrophomina spp. previously reported (Huda-Shakirah et al. 2019; Machado et al. 2019; Santos et al. 2020; Poudel et al. 2021) using ClustalW. Alignments (ITS and TEF-1α) were concatenated to generate a maximum likelihood tree using MEGA7. The novel isolates grouped into the M. euphorbiicola clade with 95% of bootstrap support. Stevia plants cv. 'Katupyry' were grown in 10 cm-diameter nursery bags containing autoclaved sandy soil and kept under greenhouse conditions (28 ± 5°C; 16 h photoperiod). Fifteen plants per isolate (n=75) were inoculated by adding 20 g of rice infested with M. euphorbiicola to each plant. Infested grains were distributed around the crown of the plant at a depth of 0.5 cm; non-infested rice was added to four control plants. Lower-stem lesions and microsclerotia of M. euphorbiicola developed on all inoculated plants. No lesions or microsclerotia were observed on control plants. The M. euphoribiicola fungus was re-isolated from inoculated stevia plants but not from the non-infested rice treated plants. Koch's postulates were repeated twice with similar results. Previously, M. phaseolina was reported causing charcoal rot on stevia in Egypt (Hilal and Baiuomy 2000), and in North Carolina, USA (Koehler and Shew 2017). However, Paraguayan isolates grouped with isolates of M. euphorbiicola based on the combined sequences of the ITS and TEF-1α regions. Machado et al. (2019) reported M. euphorbiicola causing charcoal rot on castor bean (Ricinus communis) and bellyache bush (Jatropha gossypifolia) in Brazil, which borders northeast Paraguay, a major stevia production area. This pathogen has a significant impact on stevia production during hot, dry weather by reducing the number of harvestable plants and increasing replanting costs in perennial production systems.}, number={1}, journal={PLANT DISEASE}, author={Sanabria-Velazquez, Andres D. D. and Cubilla, Alberto and Flores-Giubi, Maria Eugenia and Barua, Javier E. E. and Romero-Rodriguez, Cristina and Enciso-Maldonado, Guillermo A. A. and Thiessen, LindseyD D. and Shew, H. David}, year={2023}, month={Jan} }
 @article{sanabria-velazquez_enciso-maldonado_maidana-ojeda_diaz-najera_ayvar-serna_thiessen_shew_2023, title={Integrated Pathogen Management in Stevia Using Anaerobic Soil Disinfestation Combined with Different Fungicide Programs in USA, Mexico, and Paraguay}, volume={13}, ISSN={["2073-4395"]}, DOI={10.3390/agronomy13051358}, abstractNote={Stevia is a semi-perennial crop grown to obtain the diterpene glycosides in its leaves, which are processed to manufacture non-caloric sweeteners. Anaerobic soil disinfestation (ASD) and fungicide application were evaluated for the management of stevia stem rot (SSR) and Septoria leaf spot (SLS) in lab and field experiments. In 2019 and 2021, experiments using carbon sources for ASD were carried out in microplots at NCSU (Clayton, NC, USA). In 2020/21 and 2021/22 seasons, field experiments were conducted at CSAEGRO, Mexico (MX) and CEDIT, Paraguay (PY) using a 2 × 3 factorial design with two ASD treatments and three fungicide treatments. ASD treatments included soil amended with cornmeal (MX) or wheat bran (PY) at a rate of 20.2 Mg ha−1, molasses at 10.1 Mg ha−1, and non-amended controls. Fungicide applications included chemical (azoxystrobin), organic (pyroligneous acid, PA), and a non-treated control. ASD was effective in reducing sclerotia viability of Sclerotium rolfsii in laboratory assays (p < 0.0001) and microplot trials (p < 0.0001) in NC. During field trials, the viability of sclerotia was significantly reduced (p < 0.0001) in soils amended with cornmeal + molasses or wheat bran + molasses as carbon sources for ASD. While there was no significant effectiveness of ASD in reducing SLS in 2020 and 2021 or SSR in MX 2020 field trials (p = 0.83), it did exhibit efficacy on SSR in 2021 (p < 0.001). The application of fungicides was significantly effective in reducing SSR (p = 0.01) and SLS (p = 0.001), with azoxystrobin being the most consistent and PA not being statistically different from the control or azoxystrobin. The effects of ASD on fresh yield were inconsistent, exhibiting significant effects in Mexican fields in 2020 but not in 2021. During Paraguayan field trials, ASD only significantly interacted with fungicide applications in the dry yield in 2022. In the 2020/21 MX and 2020 PY field trials, fungicides were significantly effective in enhancing dry leaf yields, with azoxystrobin showing the highest consistency among treatments and PA variable control. In conclusion, utilizing ASD alongside organic fungicides can be a valuable tool for stevia farmers when the use of chemical fungicides is limited. Further research is required to enhance consistency and reduce the costs associated with these treatments under diverse edaphoclimatic conditions.}, number={5}, journal={AGRONOMY-BASEL}, author={Sanabria-Velazquez, Andres D. and Enciso-Maldonado, Guillermo A. and Maidana-Ojeda, Marco and Diaz-Najera, Jose F. and Ayvar-Serna, Sergio and Thiessen, Lindsey D. and Shew, H. David}, year={2023}, month={May} }
 @article{jin_mccorkle_cornish_carbone_lewis_shew_2022, title={Adaptation of Phytophthora nicotianae to Multiple Sources of Partial Resistance in Tobacco}, volume={106}, ISSN={["1943-7692"]}, DOI={10.1094/PDIS-06-21-1241-RE}, abstractNote={ Host resistance is an important tool in the management of black shank disease of tobacco. Race development leads to rapid loss of single-gene resistance, but the adaptation by Phytophthora nicotianae to sources of partial resistance from Beinhart 1000, Florida 301, and the Wz gene region introgressed from Nicotiana rustica is poorly characterized. In greenhouse environments, host genotypes with quantitative trait loci (QTLs) conferring resistance from multiple sources were initially inoculated with an aggressive isolate of race 0 or race 1 of P. nicotianae. The most aggressive isolate was selected after each of six host generations to inoculate the next generation of plants. The race 0 isolate demonstrated a continuous gradual increase in disease severity and percentage root rot on all sources of resistance except the genotype K 326 Wz/–, where a large increase in both was observed between generations 2 and 3. Adaptation by the race 0 isolate on Beinhart 1000 represents the first report of adaptation to this genotype by P. nicotianae. The race 1 isolate did not exhibit significant increases in aggressiveness over generations but exhibited a large increase in aggressiveness on K 326 Wz/– between generations 3 and 4. Molecular characterization of isolates recovered during selection was completed via double digest restriction-site associated DNA sequencing, but no polymorphisms were associated with the observed changes in aggressiveness. The rapid adaptation to Wz resistance and the gradual adaptation to other QTLs highlights the need to study the nature of Wz resistance and to conduct field studies on the efficacy of resistance gene rotation for disease management. }, number={3}, journal={PLANT DISEASE}, author={Jin, Jing and McCorkle, Kestrel L. and Cornish, Vicki and Carbone, Ignazio and Lewis, Ramsey S. and Shew, H. David}, year={2022}, month={Mar}, pages={906–917} }
 @article{jin_shew_2022, title={Impacts of Continued Exposure to a Susceptible Host Genotype on Aggressiveness of Phytophthora nicotianae Isolates Adapted to Multiple Sources of Partial Resistance}, volume={106}, ISSN={["1943-7692"]}, DOI={10.1094/PDIS-09-20-1972-RE}, abstractNote={ Pathogen adaptation can threaten the durability of partial resistance. Mixed plantings of susceptible and partially resistant varieties may prolong the effectiveness of partial resistance, but little is known about how continued exposure to a susceptible genotype can change the aggressiveness of pathogen isolates adapted to a source of partial resistance. The objective of this study was to examine the effects of continued exposure to a highly susceptible tobacco genotype on isolates of Phytophthora nicotianae that had been adapted to partial resistance. Isolates of P. nicotianae previously adapted to two sources of partial resistance were continually exposed to either the original host of adaptation or a susceptible host. After six generations of host exposure, isolates obtained from the partially resistant and the susceptible hosts were compared for their aggressiveness on the resistant host and for differences in expression of genes associated with pathogenicity and aggressiveness. Results suggested that exposure to the susceptible tobacco genotype reduced aggressiveness of isolates adapted to partial resistance in K 326 Wz/– but not of isolates adapted to partial resistance in Fla 301. Quantification of pathogenicity-associated gene expression using qRT-PCR suggested the rapid change in aggressiveness of isolates adapted to Wz-sourced partial resistance may have resulted from modification in gene expression in multiple genes. }, number={2}, journal={PLANT DISEASE}, author={Jin, Jing and Shew, H. David}, year={2022}, month={Feb}, pages={373–381} }
 @article{sanabria-velazquez_enciso-maldonado_maidana-ojeda_diaz-najera_thiessen_shew_2022, title={Validation of Standard Area Diagrams to Estimate the Severity of Septoria Leaf Spot on Stevia in Paraguay, Mexico, and the United States}, ISSN={["1943-7692"]}, DOI={10.1094/PDIS-07-22-1609-RE}, abstractNote={ Septoria leaf spot (SLS) affects stevia leaves, reducing their quality. Estimates of SLS severity on different genotypes are made to identify resistance and as a basis to compare management approaches. The use of standard area diagrams (SADs) can improve the accuracy and reliability of severity estimates. In this study, we developed new SADs with six illustrations (0.5, 1, 10, 25, 40, and 75% severity). The SADs were validated by raters with and without experience in estimating SLS. Raters evaluated 40 leaf photos with SLS severities ranging from 0 to 100% without and with the SADs. Agreement (ρc), bias (Cb), precision (r), and intracluster correlation (ρ) coefficients were significantly closer to “true” severity values when the SADs was used by inexperienced (ρc = 0.89; Cb = 0.97; r = 0.90, ρ = 0.81) and experienced (ρc = 0.94; Cb = 0.99; r = 0.95, ρ = 0.91) raters. The SADs were tested under field conditions in Paraguay, Mexico, and the United States, with inexperienced raters assigned to two groups, one SADs trained and the other not trained, that estimated SLS severity three times: first, all raters without SADs and no time limit for the estimates; second, only the SADs-trained group used SADs and no time limit; and third, only the SADs-trained group used SADs, with a time limit of 10 s imposed per specimen assessment. Agreement and reliability of SLS severity estimates significantly improved when raters used the SADs without a time limit. The use of the new SADs improved the accuracy, precision, and reliability of SLS severity estimates, enhancing the uniformity in assessment across different stevia programs. }, journal={PLANT DISEASE}, author={Sanabria-Velazquez, Andres D. and Enciso-Maldonado, Guillermo A. and Maidana-Ojeda, Marco and Diaz-Najera, Jose F. and Thiessen, Lindsey D. and Shew, H. David}, year={2022}, month={Nov} }
 @article{shi_jin_nifong_shew_lewis_2021, title={Homoeologous chromosome exchange explains the creation of a QTL affecting soil-borne pathogen resistance in tobacco}, ISSN={["1467-7652"]}, DOI={10.1111/pbi.13693}, abstractNote={Summary}, journal={PLANT BIOTECHNOLOGY JOURNAL}, author={Shi, Rui and Jin, Jing and Nifong, Jessica M. and Shew, David and Lewis, Ramsey S.}, year={2021}, month={Oct} }
 @article{jin_shi_lewis_shew_2021, title={RNAseq Reveals Differential Gene Expression Contributing to Phytophthora nicotianae Adaptation to Partial Resistance in Tobacco}, volume={11}, ISSN={["2073-4395"]}, DOI={10.3390/agronomy11040656}, abstractNote={Phytophthora nicotianae is a devastating oomycete plant pathogen with a wide host range. On tobacco, it causes black shank, a disease that can result in severe economic losses. Deployment of host resistance is one of the most effective means of controlling tobacco black shank, but adaptation to complete and partial resistance by P. nicotianae can limit the long-term effectiveness of the resistance. The molecular basis of adaptation to partial resistance is largely unknown. RNAseq was performed on two isolates of P. nicotianae (adapted to either the susceptible tobacco genotype Hicks or the partially resistant genotype K 326 Wz/Wz) to identify differentially expressed genes (DEGs) during their pathogenic interactions with K 326 Wz/Wz and Hicks. Approximately 69% of the up-regulated DEGs were associated with pathogenicity in the K 326 Wz/Wz-adapted isolate when sampled following infection of its adapted host K 326 Wz/Wz. Thirty-one percent of the up-regulated DEGs were associated with pathogenicity in the Hicks-adapted isolate on K 326 Wz/Wz. A broad spectrum of over-represented gene ontology (GO) terms were assigned to down-regulated genes in the Hicks-adapted isolate. In the host, a series of GO terms involved in nuclear biosynthesis processes were assigned to the down-regulated genes in K 326 Wz/Wz inoculated with K 326 Wz/Wz-adapted isolate. This study enhances our understanding of the molecular mechanisms of P. nicotianae adaptation to partial resistance in tobacco by elucidating how the pathogen recruits pathogenicity-associated genes that impact host biological activities.}, number={4}, journal={AGRONOMY-BASEL}, author={Jin, Jing and Shi, Rui and Lewis, Ramsey Steven and Shew, Howard David}, year={2021}, month={Apr} }
 @article{xiao_qiu_tao_zhang_chen_reberg-horton_shi_shew_zhang_hu_2020, title={Biological controls over the abundances of terrestrial ammonia oxidizers}, volume={29}, ISSN={["1466-8238"]}, DOI={10.1111/geb.13030}, abstractNote={Abstract}, number={2}, journal={GLOBAL ECOLOGY AND BIOGEOGRAPHY}, author={Xiao, Rui and Qiu, Yunpeng and Tao, Jinjin and Zhang, Xuelin and Chen, Huaihai and Reberg-Horton, S. Chris and Shi, Wei and Shew, H. David and Zhang, Yi and Hu, Shuijin}, year={2020}, month={Feb}, pages={384–399} }
 @article{koehler_larkin_shew_2020, title={Under the Scope: Microscopy Techniques to Visualize Plant Anatomy & Measure Structures}, volume={82}, ISSN={["1938-4211"]}, DOI={10.1525/abt.2020.82.4.257}, abstractNote={Microscopy and stained specimens engage students visually as they learn about plant anatomy, a topic covered in many biology and introductory science courses. In this activity, students section plant material and prepare specimens to view under a brightfield microscope. Using a camera or cell phone, images of microscope slide contents allow students to label plant parts and engage in discussions with peers. The addition of scale bars to their images will allow a better understanding of the relationships of the various structures observed in the functioning of plants.}, number={4}, journal={AMERICAN BIOLOGY TEACHER}, author={Koehler, Alyssa M. and Larkin, Maximo T. and Shew, H. David}, year={2020}, month={Apr}, pages={257–260} }
 @article{hutchens_gannon_shew_kerns_2019, title={Effect of post-application irrigation on fungicide movement and efficacy against Magnaporthiopsis poae}, volume={122}, ISSN={["1873-6904"]}, DOI={10.1016/j.cropro.2019.04.027}, abstractNote={Management of many crown and root diseases of turfgrasses includes the use of fungicides. The physicochemical properties of the fungicides used vary greatly, but most have low mobility and are not phloem mobile, which results in little active ingredient present in the basal and underground structures of turfgrass plants. Two studies were conducted in a laboratory setting to determine the effects of post-application irrigation amounts (0, 0.3, 0.6, 1.3, and 2.5 cm) on the distribution of 14C myclobutanil and 14C tebuconazole in a soil profile of 90% sand and 10% peat moss by volume. In addition, growth chamber experiments were conducted to examine the effect of post-application irrigation amount on azoxystrobin efficacy against summer patch (Magnaporthiopsis poae) in ‘Penn A-4’ creeping bentgrass (Agrostis stolonifera L.). The creeping bentgrass was treated with azoxystrobin and immediately irrigated with 0, 0.25, 0.3, or 0.6 cm of irrigation. Lastly, an in vitro fungicide sensitivity assay was conducted on three M. poae isolates to determine their sensitivities to two succinate dehydrogenase inhibitors (SDHIs), three demethylation inhibitors (DMIs), and four strobilurins (QoIs) to determine if fungicide concentrations in the soil profile reached levels high enough to suppress fungal growth. In both 14C experiments, more than 54% of the 14C was retained in the top 5 cm of soil for all irrigation treatments. For the 14C myclobutanil experiment, lysimeters treated with 2.5 cm of post-application irrigation resulted in 3.9% of 14C recovered in the 7.6–10.2 cm sampling depth, which was higher than all other irrigation treatments. Post-application irrigation at 2.5 cm in the 14C tebuconazole experiment yielded 6.3% of the 14C at the 7.6–10.2 cm sampling depth and 2.3% at the 10.2–12.7 cm sampling depth—recoveries at both depths were higher with 2.5 cm of irrigation than all other irrigation treatments. No 14C was detected below 12.7 cm for either experiment. Less disease was observed when azoxystrobin received post-application irrigation. Both 0.25 and 0.3 cm of post-application irrigation increased turf quality compared to no irrigation; moreover, 0.25 and 0.6 cm of post-application irrigation increased root length compared to no irrigation. In the in vitro fungicide sensitivity assay, isolates of M. poae were sensitive to all fungicides with only minor sensitivity to the SDHIs. In general, isolates were most sensitive to the QoIs with some variability in isolate sensitivities noted. Isolates of M. poae are sensitive to commonly used fungicides and efficacy is enhanced by post-application irrigation due to improved fungicide distribution into the soil profile.}, journal={CROP PROTECTION}, author={Hutchens, W. J. and Gannon, T. W. and Shew, H. D. and Kerns, J. P.}, year={2019}, month={Aug}, pages={106–111} }
 @article{koehler_shew_2019, title={Effects of fungicide applications on root-infecting microorganisms and overwintering survival of perennial stevia}, volume={120}, ISSN={0261-2194}, url={http://dx.doi.org/10.1016/J.CROPRO.2019.02.010}, DOI={10.1016/J.CROPRO.2019.02.010}, abstractNote={Koehler, A.M. and Shew, H.D. 2018. Effects of fungicide applications on root-infecting microorganisms and overwintering survival of perennial stevia. Crop Protection 117:000–000. Stevia (Stevia rebaudiana) is a perennial species emerging as a new crop in the southeastern United States. In previous studies, application of quinone outside inhibitor (QoI) fungicides enhanced overwintering survival of stevia. Greenhouse and field trials were conducted to assess the effect of multiple fungicides on plant growth, root associated microorganisms, and overwintering survival. In greenhouse trials in the absence of soilborne pathogens, no differences in plant height, shoot weight, or root system ratings were observed among treatments. In two field trials screening seven combination fungicides and one biological control, significant increases in overwintering survival of plants treated with QoI fungicides were observed. Plants were dug from the fields monthly to destructively sample root crowns and species of Fusarium, Ceratobasidium, Pythium, and Macrophomina phaseolina were consistently isolated. Abundant microsclerotia from M. phaseolina were observed on stems of plants that did not survive winter. In seven sample months at each of the two field trials, non-fungicide treated plants had the lowest root weights. This study is one of the first to evaluate interactions between fungicide use and root associated fungi in a perennial crop and provides a framework to further investigate the role of root-associated fungi in overwintering survival.}, journal={Crop Protection}, publisher={Elsevier BV}, author={Koehler, A.M. and Shew, H.D.}, year={2019}, month={Jun}, pages={13–20} }
 @article{koehler_larkin_rogers_carbone_cubeta_shew_2019, title={Identification and characterization of Septoria steviae as the causal agent of Septoria leaf spot disease of stevia in North Carolina}, volume={111}, ISSN={0027-5514 1557-2536}, url={http://dx.doi.org/10.1080/00275514.2019.1584503}, DOI={10.1080/00275514.2019.1584503}, abstractNote={ABSTRACT Stevia (Stevia rebaudiana) is an emerging perennial crop in the southeastern United States. A Septoria leaf spot disease of stevia was first identified on field plantings in Japan in 1978. The pathogen was named Septoria steviae based on a morphological characterization. In 2015, a species of Septoria with morphological characters of S. steviae was isolated from field and greenhouse-grown stevia plants with leaf spot symptoms in North Carolina. In this study, 12 isolates obtained from diseased stevia plants in 2015 and 2016 were characterized and compared with reference strains of S. steviae. Comparisons were based on conidial and pycnidial morphology and multilocus sequence analysis of actin (ACT), β-tubulin (BT), calmodulin (CAL), nuc rDNA internal transcribed spacers (ITS1-5.8S-ITS2 = ITS), nuc rDNA 28S subunit (28S), RNA polymerase II second largest subunit (RPB2), and translation elongation factor-1α (TEF1). Measurements of conidia and pycnidia from symptomatic field leaves and 12 pure cultures grown on nutrient medium were consistent with those previously reported for ex-type strains of S. steviae. North Carolina strains formed a well-supported monophyletic group with ex-type strains of S. steviae. This study represents the first genetic characterization of S. steviae in the United States and provides an experimental framework to elucidate the genetic diversity and disease ecology of field populations of S. steviae.}, number={3}, journal={Mycologia}, publisher={Informa UK Limited}, author={Koehler, Alyssa M. and Larkin, Maximo T. and Rogers, Layne W. and Carbone, Ignazio and Cubeta, Marc A. and Shew, H. David}, year={2019}, month={Apr}, pages={456–465} }
 @article{mccorkle_drake-stowe_lewis_shew_2018, title={Characterization of Phytophthora nicotianae Resistance Conferred by the Introgressed Nicotiana rustica Region, Wz, in Flue-Cured Tobacco}, volume={102}, ISSN={["1943-7692"]}, DOI={10.1094/pdis-03-17-0339-re}, abstractNote={ Black shank, caused by Phytophthora nicotianae, is one of the most important diseases affecting tobacco worldwide and is primarily managed through use of host resistance. An additional source of resistance to P. nicotianae, designated as Wz, has been introgressed into Nicotiana tabacum from N. rustica. The Wz gene region confers high levels of resistance to all races, but has not been characterized. Our study found Wz-mediated resistance is most highly expressed in the roots, with only a slight reduction in stem-lesion size in Wz genotypes compared with susceptible controls. No substantial relationships were observed between initial inoculum levels and disease development on Wz genotypes, which is generally consistent with qualitative or complete resistance. Isolates of P. nicotianae adapted for five host generations on plants with the Wz gene caused higher disease severity than isolates adapted on Wz plants for only one host generation. Wz-adapted isolates did not exhibit increased aggressiveness on genotypes with other sources of partial resistance, suggesting pathogen adaptation was specific to the Wz gene. To reduce potential for pathogen population shifts with virulence on Wz genotypes, Wz should be combined with other resistance sources and rotation of varying black shank resistance mechanisms is also recommended. }, number={2}, journal={PLANT DISEASE}, author={McCorkle, Kestrel L. and Drake-Stowe, Katherine and Lewis, Ramsey S. and Shew, David}, year={2018}, month={Feb}, pages={309–317} }
 @article{gallup_mccorkle_ivors_shew_2018, title={Characterization of the Black Shank Pathogen, Phytophthora nicotianae, Across North Carolina Tobacco Production Areas}, volume={102}, ISSN={["1943-7692"]}, DOI={10.1094/pdis-02-17-0295-re}, abstractNote={ Black shank disease of tobacco, caused by the oomycete Phytophthora nicotianae, is a major threat to production in the United States and tobacco-producing areas worldwide. In a statewide survey of North Carolina, the rapid shift from race 0 to race 1 was documented. Collected pathogen isolates were characterized phenotypically for mating type and mefenoxam sensitivity, and genotypically by comparing sequences from three cytoplasmic and two nuclear regions. Both the A1 and A2 mating types were found throughout the state. When both mating types were recovered from the same field, pairings of isolates yielded viable oospores, indicating for the first time the potential for sexual sporulation by P. nicotianae in natural populations. Because the loss of complete resistance required a renewed use of the fungicide mefenoxam, a subset of the survey isolates was screened for sensitivity to the fungicide. All isolates were sensitive, with a mean effective concentration to inhibit 50% of hyphal growth of 0.4 μg/ml that was similar across mating types and races. Molecular characterization of 226 isolates revealed that the pathogen exists as multiple clonal types within the state. Genetic diversity among the pathogen population and the potential for sexual recombination may help explain the ability of the pathogen to rapidly adapt to host resistance genes. }, number={6}, journal={PLANT DISEASE}, author={Gallup, Courtney A. and McCorkle, Kestrel L. and Ivors, Kelly L. and Shew, David}, year={2018}, month={Jun}, pages={1108–1114} }
 @article{qu_jiang_guo_burkey_zobel_shew_hu_2018, title={Contrasting Warming and Ozone Effects on Denitrifiers Dominate Soil N2O Emissions}, volume={52}, ISSN={["1520-5851"]}, DOI={10.1021/acs.est.8b01093}, abstractNote={Nitrous oxide (N2O) in the atmosphere is a major greenhouse gas and reacts with volatile organic compounds to create ozone (an air pollutant) in the troposphere. Climate change factors such as warming and elevated ozone (eO3) affect N2O fluxes, but the direction and magnitude of these effects are uncertain and the underlying mechanisms remain unclear. We examined the impact of simulated warming (control + 3.6 °C) and eO3 (control + 45 ppb) on soil N2O fluxes in a soybean agroecosystem. Results obtained showed that warming significantly increased soil labile C, microbial biomass, and soil N mineralization, but eO3 reduced these parameters. Warming enhanced N2O-producing denitrifers ( nirS- and nirK-type), corresponding to increases in both the rate and sum of N2O emissions. In contrast, eO3 significantly reduced both N2O-producing and N2O-consuming ( nosZ-type) denitrifiers but had no impact on N2O emissions. Further, eO3 offsets the effects of warming on soil labile C, microbial biomass, and the population size of denitrifiers but still increased N2O emissions, indicating a direct effect of temperature on N2O emissions. Together, these findings suggest that warming may promote N2O production through increasing both the abundance and activities of N2O-producing microbes, positively feeding back to the ongoing climate change.}, number={19}, journal={ENVIRONMENTAL SCIENCE & TECHNOLOGY}, author={Qu, Yunpeng and Jiang, Yu and Guo, Lijin and Burkey, Kent O. and Zobel, Richard W. and Shew, H. David and Hu, Shuijin}, year={2018}, month={Oct}, pages={10956–10966} }
 @article{koehler_shew_2018, title={Field efficacy and baseline sensitivity of Septoria steviae to fungicides used for managing Septoria leaf spot of stevia}, volume={109}, ISSN={["1873-6904"]}, DOI={10.1016/j.cropro.2018.03.006}, abstractNote={Koehler, A.M. and Shew, H.D. 2018. Field efficacy and baseline sensitivity of Septoria steviae to fungicides used for managing Septoria leaf spot of stevia. Crop Protection 106:000–000. Stevia (Stevia rebaudiana) is an herbaceous perennial emerging as a new crop in the southeastern US. Septoria leaf spot caused by Septoria steviae is present across all production areas in North Carolina, causing leaf lesions that expand and result in total defoliation when left unmanaged. Fungicide efficacy trials for management of Septoria leaf spot were conducted over 2 years at two field sites. Seven fungicides, single or combination products, reduced disease severity and increased yield compared to non-fungicide treated controls. Azoxystrobin, chlorothalonil, fluopyram, fluxapyroxad, pyraclostrobin, and tebuconazole were screened using an in vitro assay to establish sensitivity profiles for 10 isolates of S. steviae that had received 0 or 1 year of fungicide exposure. All S. steviae isolates were sensitive to all fungicides evaluated. Successful management of Septoria leaf spot is critical for long term establishment of stevia as a crop in the southeast US.}, journal={CROP PROTECTION}, author={Koehler, A. M. and Shew, H. D.}, year={2018}, month={Jul}, pages={95–101} }
 @article{koehler_shew_2018, title={First Report of Charcoal Rot of Stevia Caused by Macrophomina phaseolina in North Carolina}, volume={102}, ISSN={["1943-7692"]}, DOI={10.1094/pdis-05-17-0693-pdn}, abstractNote={HomePlant DiseaseVol. 102, No. 1First Report of Charcoal Rot of Stevia Caused by Macrophomina phaseolina in North Carolina PreviousNext DISEASE NOTES OPENOpen Access licenseFirst Report of Charcoal Rot of Stevia Caused by Macrophomina phaseolina in North CarolinaA. M. Koehler and H. D. ShewA. M. Koehler†Corresponding author: A. M. Koehler; E-mail: E-mail Address: [email protected]Search for more papers by this author and H. D. ShewSearch for more papers by this authorAffiliationsAuthors and Affiliations A. M. Koehler † H. D. Shew , Department of Entomology and Plant Pathology, North Carolina State University, Raleigh, NC 27695. Published Online:24 Oct 2017https://doi.org/10.1094/PDIS-05-17-0693-PDNAboutSections ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InRedditEmailWechat Stevia (Stevia rebaudiana [Bertoni] Bertoni) is an emerging perennial crop in the United States. Small black root lesions were first observed on overwintering crowns dug in March 2016 from a field planting of stevia in Rocky Mount, NC. Similar root lesions were observed on first year plants in Kinston and Rocky Mount, NC, throughout the 2016 growing season in fields with a history of soybean and corn rotations. Isolations from lesions were made on potato dextrose agar amended with 50 µg/ml of streptomycin sulfate and penicillin G. Isolations were incubated at room temperature (22 to 25°C) for 1 week and observed for colony morphology. Gray-black colonies that became dark with age were isolated into pure culture. Hyphae were septate with barrel-shaped cells, and numerous 50 to 150 µm microsclerotia resembling those produced by Macrophomina (Kaur et al. 2012) were present. Pathogen identification was confirmed by sequencing the internal spacer (ITS) region of ribosomal DNA. DNA was extracted from mycelia with the Qiagen DNEasy Plant Mini Kit (Qiagen, Valencia, CA) and subjected to a PCR using universal primers ITS 4,5. Isolates were identified as Macrophomina phaseolina (100% sequence identity with GenBank accession no. KF951775.1). Koch’s postulates were confirmed on 10-week-old stevia plants, cv. G3, grown in 8-cm-diameter pots in the greenhouse. Ten 6.75-mm agar plugs were buried 1 cm deep approximately 2 cm from the base of the plant in each of six replicate sterile pots. Plants were observed over a 6-week period for symptom development, at which time root necrosis similar to field symptoms was evident on all inoculated plants. Noninoculated plants did not develop symptoms. M. phaseolina was reisolated from necrotic inoculated roots and confirmed by morphology and sequencing. To our knowledge, this is the first report of M. phaseolina causing charcoal rot of stevia in North America. Hilal and Baiuomy (2000) reported M. phaseolina as the causal agent of charcoal rot on stevia in Egypt. At this time, no fungicides are registered for stevia. Since stevia is often grown as a perennial rotation crop, and M. phaseolina was present year-round in roots of stevia, it will be important to determine if this pathogen becomes more damaging over a three year production cycle and reaches levels that may have negative impacts on rotation crops.References:Hilal, A., and Baiuomy, M. 2000. Egypt. J. Agric. Res. 78:1435. Google ScholarKaur, S., et al. 2012. Crit. Rev. Microbiol. 38:136. https://doi.org/10.3109/1040841X.2011.640977 Crossref, ISI, Google ScholarDetailsFiguresLiterature CitedRelated Vol. 102, No. 1 January 2018SubscribeISSN:0191-2917e-ISSN:1943-7692 Metrics Article History Issue Date: 20 Dec 2017Published: 24 Oct 2017First Look: 29 Aug 2017Accepted: 26 Aug 2017 Pages: 241-241 Information© 2018 The American Phytopathological SocietyCited byFirst Report of Macrophomina euphorbiicola Causing Charcoal Rot of Stevia in ParaguayAndres D. Sanabria-Velazquez, Alberto Cubilla, Maria Eugenia Flores-Giubi, Javier E. Barua, Cristina Romero-Rodríguez, Guillermo A. Enciso-Maldonado, Lindsey D. Thiessen, and H. David Shew10 January 2023 | Plant Disease, Vol. 107, No. 1Charcoal rot of Stevia rebaudiana caused by Macrophomina phaseolina in Brazil10 August 2022 | Journal of Plant Pathology, Vol. 104, No. 4Different histone deacetylase inhibitors reduce growth, virulence as well as changes in the morphology of the fungus Macrophomina phaseolina (Tassi) Goid28 February 2022 | World Journal of Microbiology and Biotechnology, Vol. 38, No. 4Macrophomina phaseolina (charcoal rot of bean/tobacco)CABI Compendium, Vol. CABI CompendiumTrichoderma asperellum as a preventive and curative agent to control Fusarium wilt in Stevia rebaudianaBiological Control, Vol. 155Nondestructive Sampling to Monitor Macrophomina phaseolina Root Colonization in Overwintering SteviaLayne W. Rogers and Alyssa M. Koehler24 March 2021 | Plant Health Progress, Vol. 22, No. 2Full Issue PDF9 June 2022 | Plant Health Progress, Vol. 22, No. 2One stop shop III: taxonomic update with molecular phylogeny for important phytopathogenic genera: 51–75 (2019)17 September 2019 | Fungal Diversity, Vol. 98, No. 1Effects of fungicide applications on root-infecting microorganisms and overwintering survival of perennial steviaCrop Protection, Vol. 120}, number={1}, journal={PLANT DISEASE}, author={Koehler, A. M. and Shew, H. D.}, year={2018}, month={Jan}, pages={241–241} }
 @article{jahnke_dole_shew_2018, title={Prolonged Shipping and Fluctuating Temperatures Promote Gray Mold Development and Leaf Yellowing on Geranium Liners}, volume={28}, ISSN={["1943-7714"]}, DOI={10.21273/HORTTECH04149-18}, abstractNote={Postharvest environments during storage and shipping are often conducive to plant stress and disease development. Liners of four cultivars of geraniums (Pelargonium ×hortorum) were evaluated every 2 days for their susceptibility to gray mold (Botrytis cinerea) and leaf yellowing over an 8-day simulated shipping period at either constant air temperature of 15 °C or variable air temperatures cycling every 24 hours between 10 and 30 °C. The latter treatment was created using air temperature logs of commercial liner shipments sent to five locations during Spring 2016 and Fall 2016. We sprayed a spore suspension of 2 × 104 or 2 × 106 to inoculate liners before they were subjected to the two temperature treatments. Disease ratings did not reach significant levels for the dry control until day 6 of storage. Regardless of the spore concentration, ratings were similar for inoculated cuttings. Independent of the storage temperature and spore concentration, liners developed minor lesions by day 2 of storage. Cultivars varied slightly in disease ratings, with Tango Dark Red being the most susceptible, followed by Patriot Bright Red, Patriot Rose Pink, and Americana Red. During the 8-day incubation period, ‘Patriot Rose Pink’ developed the most leaf yellowing compared with the other three cultivars. Liners that experienced variable air temperatures had marginal leaf yellowing by day 2, and this yellowing increased throughout the experiment. Liners placed at 15 °C had ≈50% less leaf yellowing compared with liners exposed to variable air temperatures until day 8, when leaf yellowing was similar between the two air temperature treatments. Disease caused by B. cinerea was avoided when simulated shipping was 2 days or fewer, and a stable air temperature of 15 °C reduced leaf yellowing on geranium liners compared with variable air temperatures.}, number={6}, journal={HORTTECHNOLOGY}, author={Jahnke, Nathan J. and Dole, John M. and Shew, H. David}, year={2018}, month={Dec}, pages={711–718} }
 @article{koehler_shew_2017, title={Enhanced Overwintering Survival of Stevia by Qol Fungicides Used for Management of Sclerotium rolfsii}, volume={101}, ISSN={["1943-7692"]}, DOI={10.1094/pdis-02-17-0277-re}, abstractNote={ Stevia (Stevia rebaudiana) is a herbaceous perennial under evaluation as a new crop in the southeastern United States. Stem rot caused by Sclerotium rolfsii is common in stevia plantings in North Carolina, with symptoms including wilting, root and stem necrosis, and plant death. Fungicide efficacy trials for management of S. rolfsii were conducted over 2 years. Fungicides evaluated included azoxystrobin, flutolanil, and tebuconazole applied at three timings. Azoxystrobin applied to transplants 1 week prior to planting had the lowest area under the disease progress curve values across all trials. Fungicide plots were also used to evaluate overwintering of stevia. End-of-season stand counts were compared with spring emergence counts to quantify overwintering survival. In spring 2015, plots treated with azoxystrobin in 2014 had greater overwintering survival (78%) than other fungicide treatments (38%) and the control (38%). Similar results were obtained at two locations in spring 2016 in plots treated with azoxystrobin or pyraclostrobin in 2015. Successful overwintering of stevia directly impacts the profitability of second- and third-year harvests and enhances the likelihood of long-term establishment of stevia as a viable crop. Future studies will be directed at elucidating the mechanism of the enhanced overwintering survival of plants treated with quinone outside inhibitor fungicides. }, number={8}, journal={PLANT DISEASE}, author={Koehler, A. M. and Shew, H. D.}, year={2017}, month={Aug}, pages={1417–1421} }
 @article{koehler_lookabaugh_shew_shew_2017, title={First report of pythium root rot of stevia caused by Pythium myriotylum, P. irregulare, and P. aplzanidermatum in North Carolina}, volume={101}, number={7}, journal={Plant Disease}, author={Koehler, A. M. and Lookabaugh, E. C. and Shew, B. B. and Shew, H. D.}, year={2017}, pages={1331–1332} }
 @article{koehler_shew_2017, title={Seasonal dynamics and fungicide sensitivity of organisms causing brown patch of tall fescue in North Carolina}, volume={109}, ISSN={["1557-2536"]}, DOI={10.1080/00275514.2017.1377587}, abstractNote={ABSTRACT Brown patch, caused by multiple species of Rhizoctonia and Rhizoctonia-like fungi, is the most severe summer disease of tall fescue in home lawns across the southeastern United States. Home lawns were surveyed in central North Carolina from 2013 to 2015 to determine the organisms present during typical epidemics of brown patch in tall fescue. Isolates of Rhizoctonia and Rhizoctonia-like fungi were obtained by sampling 147 locations in July 2013 and May and July 2014. In addition, 11 sites were sampled once a week for 12 consecutive weeks from late May to the end of July 2015. All isolates were identified to species and anastomosis group with nuc rDNA internal transcribed spacer (ITS) sequence analysis. Isolations from brown patch lesions in May 2014 predominately yielded Ceratobasidium cereale (77% of the organisms recovered), whereas the organisms recovered in July 2013 and 2014 were R. solani AG 2-2-IIIB (44%), R. solani AG 1-IB (37%), and R. zeae (14%). In 2015, Ceratobasidium cereale was isolated from all 11 locations in May but was replaced by Rhizoctonia species in June and July. Sensitivity of the May 2014 isolates to multiple concentrations of the fungicides azoxystrobin, flutolanil, fluxapyroxad, and propiconazole was compared with sensitivity of isolates collected in 2003, to determine whether multiple years of exposure to fungicides applied for brown patch control had altered fungicide sensitivity. Historical isolates of R. solani, which had never been exposed to fungicide applications for brown patch control, were also included for comparison. Mean EC50 values (concentration of fungicide needed to inhibit mycelial growth by 50%) varied across fungicides and species, but no resistance was observed, and there was no apparent shift in sensitivity over the years. An additional 94 isolates from 2015 were screened against azoxystrobin, flutolanil, fluxapyroxad, and propiconazole, and fungicide insensitivity was not observed.}, number={4}, journal={MYCOLOGIA}, author={Koehler, Alyssa M. and Shew, H. David}, year={2017}, pages={667–675} }
 @article{steede_ma_eickholt_drake-stowe_kernodle_shew_danehower_lewis_2017, title={The Tobacco Trichome Exudate Z-abienol and Its Relationship With Plant Resistance to Phytophthora nicotianae}, volume={101}, ISSN={["1943-7692"]}, DOI={10.1094/pdis-10-16-1512-re}, abstractNote={ In previous research, we discovered a favorable quantitative trait locus (QTL) in cigar tobacco cultivar ‘Beinhart 1000’ designated as Phn15.1, which provides a high level of partial resistance to the black shank disease caused by Phytophthora nicotianae. A very close genetic association was also found between Phn15.1 and the ability to biosynthesize Z-abienol, a labdanoid diterpene exuded by the trichomes onto above-ground plant parts, and that imparts flavor and aroma characteristics to Oriental and some cigar tobacco types. Because accumulation of Z-abienol is considered to be undesirable for cultivars of other tobacco types, we herein describe a series of experiments to gain insight on whether this close association is due to genetic linkage or pleiotropy. First, in an in vitro bioassay, we observed Z-abienol and related diterpenes to inhibit hyphal growth of P. nicotianae at concentrations between 0.01 and 100 ppm. Secondly, we field-tested transgenic versions of Beinhart 1000 carrying RNAi constructs for downregulating NtCPS2 or NtABS, two genes involved in the biosynthesis of Z-abienol. Thirdly, we also field tested a recombinant inbred line population segregating for a truncation mutation in NtCPS2 leading to an interrupted Z-abienol pathway. We observed no correlation between field resistance to P. nicotianae and the ability to accumulate Z-abienol in either the transgenic materials or the mapping population. Results suggest that, although Z-abienol may affect P. nicotianae when applied at high concentrations in in vitro assays, the compound has little effect on black shank disease development under natural field conditions. Thus, it should be possible to disassociate Phn15.1-mediated black shank resistance identified in cigar tobacco cultivar Beinhart 1000 from the ability to accumulate Z-abienol, an undesirable secondary metabolite for burley and flue-cured tobacco cultivars. }, number={7}, journal={PLANT DISEASE}, author={Steede, William T. and Ma, Justin M. and Eickholt, David P. and Drake-Stowe, Katherine E. and Kernodle, Sheri P. and Shew, H. David and Danehower, David A. and Lewis, Ramsey S.}, year={2017}, month={Jul}, pages={1214–1221} }
 @article{pettersson_frampton_rönnberg_shew_benson_kohlway_escanferla_cubeta_2016, title={Increased diversity of Phytophthora species in Fraser fir Christmas tree plantations in the Southern Appalachians}, volume={32}, ISSN={0282-7581 1651-1891}, url={http://dx.doi.org/10.1080/02827581.2016.1265144}, DOI={10.1080/02827581.2016.1265144}, abstractNote={ABSTRACT Phytophthora root rot (PRR) disease afflicts significant economic losses to the Fraser fir Christmas tree industry. In previous surveys conducted in 1972 and from 1997 to 1998 in North Carolina, the incidence of PRR was ∼9.5% with Phytophthora cinnamomi identified as the predominant causal species isolated from infected roots of Fraser fir. Due to increased use of out-of-state planting stock since 2000, we suspected increased diversity of Phytophthora species. During 2014, we surveyed Fraser fir Christmas tree plantations in the Southern Appalachians of North Carolina, Tennessee and Virginia to determine the occurrence of pathogenic root-rotting species of Phytophthora. A weighted sampling strategy based on Christmas tree acreage was deployed to collect symptomatic Fraser fir roots from 103 commercial production fields in 14 counties. Six species of Phytophthora were isolated from infected roots sampled from 82 sites in 13 counties. Phytophthora cinnamomi, P. cryptogea and P. pini represented 70.3%, 23.1% and 1.1% of the 91 isolates. Phytophthora citrophthora, P. europaea and P. sansomeana accounted for the remaining 5.5% of the isolates and have not been identified in previously published Fraser fir surveys conducted in the region. The pathogenicity of P. citrophthora on Fraser fir was confirmed based on completion of Koch’s postulates.}, number={5}, journal={Scandinavian Journal of Forest Research}, publisher={Informa UK Limited}, author={Pettersson, M. and Frampton, J. and Rönnberg, J. and Shew, H. D. and Benson, D. M. and Kohlway, W. H. and Escanferla, M. E. and Cubeta, M. A.}, year={2016}, month={Dec}, pages={412–420} }
 @article{mercado cardenas_galvan_barrera_rodriguero_carmona_march_ramallo_shew_2015, title={Molecular identification and pathogenicity of Rhizoctonia spp. from tobacco growing areas in northwestern Argentina}, volume={40}, ISSN={["1983-2052"]}, DOI={10.1007/s40858-015-0035-7}, abstractNote={In Argentina, more than 60 % of the tobacco crops are grown in the northwestern part of the country and where Rhizoctonia solani leads to a reduction in crop yield and quality. In this study, 35 isolates of Rhizoctonia were obtained from 32 tobacco fields in northwestern Argentina and characterized by both morphological and molecular approaches. Based on the variability in the ITS region, isolates were identified as R. solani (80 %), Waitea circinata var. zeae (Rhizoctonia zeae) (8 %) and binucleate Rhizoctonia (8 %). Most isolates of R. solani belonged to the anastomosis groups (AGs) AG 4 HG-I (44 %), AG 2-1 (41 %) and AG 4 HG-III (13 %). Isolates of binucleate Rhizoctonia belonged to AG-F and AG-P of Ceratobasidium sp. Morphological variability was higher within isolates of AG 2-1 and AG 4 HG-III than within those of AG 4 HG-I. Aggressiveness of the isolates towards tobacco seedlings was assessed in the greenhouse. Isolates of AG 2-1 were the most aggressive on leaves, causing target spot, whereas isolates of AG 4 HG-I were the most aggressive on stems and roots, causing damping-off.}, number={3}, journal={TROPICAL PLANT PATHOLOGY}, author={Mercado Cardenas, Guadalupe E. and Galvan, Marta Z. and Barrera, Viviana A. and Rodriguero, Marcela S. and Carmona, Marcelo A. and March, Guillermo J. and Ramallo, Ana C. and Shew, H. David}, year={2015}, month={Jun}, pages={160–168} }
 @article{koehler_shew_2014, title={First Report of Stem Rot of Stevia Caused by Sclerotinia sclerotiorum in North Carolina}, volume={98}, ISSN={["1943-7692"]}, DOI={10.1094/pdis-03-14-0307-pdn}, abstractNote={ Stevia (Stevia rebaundiana Bertoni) is an emerging perennial crop in the United States. The crop is grown for 3 to 5 years with two harvests per growing season. Stevia contains numerous glycosides that are used as a natural noncaloric sweetener, and in 2008 was approved by the USDA as a sugar substitute. In commercial plantings of second-year stevia in North Carolina, diseased plants were observed in April and May of 2013. Diseased plants were observed in several counties in the state in fields that had been planted primarily in a corn-soybean rotation prior to stevia planting. Symptoms included wilting, chlorotic leaves, necrotic leaves at the base of the stem, bleached stem lesions, and dead plants. Symptomatic plants often also had tufts of white hyphae present on stems and large, irregularly shaped 2- to 8-mm black sclerotia frequently were present on the base of the stem. Isolations from infected stem tissue were made on potato dextrose agar amended with 50 μg/ml of streptomycin sulfate and penicillin G. Based on hyphal and sclerotial characteristics, isolates were tentatively identified as Sclerotinia sclerotiorum (Lib.) de Bary (4). Koch's postulates were confirmed on 10-week-old Stevia plants cv. G3 grown in the greenhouse in 10-cm-diameter pots containing a sterile 1:1:1 sand, loam, media mix. Oat grains infested with one isolate obtained from diseased field plants served as the inoculum. Oats were sterilized on three consecutive days, inoculated with colonized agar plugs of S. sclerotiorum, and then incubated at room temperature until they were thoroughly colonized. Three infested oat grains were buried 1 cm deep approximately 2 cm from the base of the plant in each of the six test pots and plants were observed over a 3-week period for symptoms. Symptoms developed on all plants within 5 days of inoculation. Leaves began to wilt, then turned chlorotic and necrotic, with stem lesions and sclerotia present at the base of the plant. Isolations were taken from infected stem tissue and pure cultures were prepared for molecular identification. Uninoculated control plants did not develop symptoms. Pathogen identification was confirmed using universal primers ITS 4,5 and β-tubulin (2,3). Mycelium from the cultured greenhouse stem isolations were grown in potato dextrose broth. Mycelium samples were aspirated and lyophilized prior to DNA extraction. Extracted DNA was amplified through PCR with ITS and β-tubulin primers and sent for sequencing. Sequences were aligned using CLC Workbench. Sequences from ITS45 had 100% identity to S. sclerotiorum GenBank Accession No. KF859933.1, confirming S. sclerotiorum as the causal organism. The β-tubulin sequence was compared against the Broad Institute S. sclerotiorum whole genome shotgun sequence and was confirmed to have 100% identity to the beta tubulin chain (5). This is the first report of S. sclerotiorum on stevia in the United States. Chang et al. (2) reported a stem rot of stevia in Canada and confirmed S. sclerotiorum as the causal organism. }, number={10}, journal={PLANT DISEASE}, author={Koehler, A. and Shew, H.}, year={2014}, month={Oct}, pages={1433–1433} }
 @article{koehler_shew_2014, title={First Report of Stem and Root Rot of Stevia Caused by Sclerotium rolfsii in North Carolina}, volume={98}, ISSN={["1943-7692"]}, DOI={10.1094/pdis-12-13-1238-pdn}, abstractNote={ Stevia (Stevia rebaundia) is an emerging crop in the United States. Once established, the crop is grown for 3 to 5 years and is typically harvested twice per growing season. Stevia leaves contain multiple glycosides that are used as a natural noncaloric sweetener that was approved by the USDA in 2008 as a sugar substitute. In commercial plantings of Stevia in North Carolina, wilting and death of plants in first- and second-year plantings were observed in 2012 and 2013. Diseased plants were observed in multiple counties in the state, with first symptoms observed in May of each year and continuing through the summer months. Prior to Stevia, these fields had been planted primarily in a corn-soybean rotation. Symptoms began as moderate to severe wilting of young shoots and chlorosis of leaves, rapidly followed by death of stems and rotting of roots. White mycelial growth was frequently observed at the base of stem tissue. Theses characteristic hyphae of Sclerotium rolfsii were often accompanied by the presence of abundant white to brown sclerotia. Isolations from infected root and stem tissue were made on potato dextrose agar amended with 50 μg/ml of streptomycin sulfate and penicillin G. Isolations from diseased tissue yielded characteristic white hyphae of S. rolfsii (1,3). Numerous sclerotia 0.5 to 2 mm in diameter developed following 4 to 7 days of mycelial growth. Sclerotia were initially white and melanized turning brown with age. To verify pathogenicity, 10-week-old Stevia seedlings were transplanted in 10-cm diameter pots containing sterile 1:1:1 sand, loam, media mix. Inoculum consisted of oat grains infested with one isolate obtained from the field plants. Oats were sterilized on three consecutive days and then inoculated with colonized agar plugs of S. rolfsii. Oats were incubated at room temperature to allow the fungus to thoroughly colonize the oats. Three infested oat grains were added to each test pot and plants were then observed over a 3-week period. Symptoms were observed within 5 days on most plants and included chlorotic leaves, bleached stems, wilting, and necrotic roots. White mycelium and abundant sclerotia were found at the base of plants. Uninoculated plants did not develop any symptoms. This is the first report of S. rolfsii on Stevia in the United States. Kamalakannan et al. (2) reported a root rot disease of Stevia in India and confirmed S. rolfsii as the causal agent. }, number={7}, journal={PLANT DISEASE}, author={Koehler, A. and Shew, H.}, year={2014}, month={Jul}, pages={1005–1005} }
 @article{cheng_booker_burkey_tu_shew_rufty_fiscus_deforest_hu_2014, title={SOIL MICROBIAL RESPONSES TO ELEVATED CO2 AND O-3 IN A NITROGEN-AGGRADING AGROECOSYSTEM}, volume={6}, ISBN={["978-1-77188-021-3"]}, DOI={10.1371/journal.pone.0021377}, abstractNote={Climate change factors such as elevated atmospheric carbon dioxide (CO2) and ozone (O3) can exert significant impacts on soil microbes and the ecosystem level processes they mediate. However, the underlying mechanisms by which soil microbes respond to these environmental changes remain poorly understood. The prevailing hypothesis, which states that CO2- or O3-induced changes in carbon (C) availability dominate microbial responses, is primarily based on results from nitrogen (N)-limiting forests and grasslands. It remains largely unexplored how soil microbes respond to elevated CO2 and O3 in N-rich or N-aggrading systems, which severely hinders our ability to predict the long-term soil C dynamics in agroecosystems. Using a long-term field study conducted in a no-till wheat-soybean rotation system with open-top chambers, we showed that elevated CO2 but not O3 had a potent influence on soil microbes. Elevated CO2 (1.5×ambient) significantly increased, while O3 (1.4×ambient) reduced, aboveground (and presumably belowground) plant residue C and N inputs to soil. However, only elevated CO2 significantly affected soil microbial biomass, activities (namely heterotrophic respiration) and community composition. The enhancement of microbial biomass and activities by elevated CO2 largely occurred in the third and fourth years of the experiment and coincided with increased soil N availability, likely due to CO2-stimulation of symbiotic N2 fixation in soybean. Fungal biomass and the fungi∶bacteria ratio decreased under both ambient and elevated CO2 by the third year and also coincided with increased soil N availability; but they were significantly higher under elevated than ambient CO2. These results suggest that more attention should be directed towards assessing the impact of N availability on microbial activities and decomposition in projections of soil organic C balance in N-rich systems under future CO2 scenarios.}, number={6}, journal={CARBON CAPTURE AND STORAGE: CO2 MANAGEMENT TECHNOLOGIES}, author={Cheng, Lei and Booker, Fitzgerald L. and Burkey, Kent O. and Tu, Cong and Shew, H. David and Rufty, Thomas W. and Fiscus, Edwin L. and Deforest, Jared L. and Hu, Shuijin}, year={2014}, pages={277–307} }
 @article{cheng_booker_burkey_tu_shew_rufty_fiscus_deforest_hu_2014, title={Soil microbial responses to elevated CO2 and O-3 in a nitrogen-aggrading agroecosystem}, DOI={10.1201/b16845-14}, journal={Carbon Capture and Storage: CO2 Management Technologies}, author={Cheng, L. and Booker, F. L. and Burkey, K. O. and Tu, C. and Shew, H. D. and Rufty, T. W. and Fiscus, E. L. and Deforest, J. L. and Hu, Shuijin}, year={2014}, pages={277–307} }
 @article{mccorkle_lewis_shew_2013, title={Resistance to Phytophthora nicotianae in Tobacco Breeding Lines Derived from Variety Beinhart 1000}, volume={97}, ISSN={["1943-7692"]}, DOI={10.1094/pdis-05-12-0480-re}, abstractNote={ Black shank, caused by Phytophthora nicotianae, is managed primarily by host resistance. The rapid emergence of race 1 eliminated the usefulness of available complete resistance, leading breeders to search for new sources of resistance. Cigar tobacco ‘Beinhart 1000’ (BH) is highly resistant to all races of P. nicotianae. Doubled-haploid (DH) lines from a cross of BH and the susceptible ‘Hicks’ were evaluated for black shank resistance, and quantitative trait loci (QTL) on linkage groups (LGs) 4 and 8 accounted for >43% of the phenotypic variation in resistance. Forty-three DH lines and parents were evaluated, and genotypes with one or both QTL from BH on LGs 4 and 8 had increased incubation periods and decreased root rot but higher final inoculum levels than genotypes with neither QTL. A low level of stem resistance was observed in BH and DH lines with the QTL from BH on LG 4 but not LG 8. Low levels of leaf resistance were seen for Hicks, BH, and DH lines with both QTL from BH on LG 4 and 8. The partial resistance from BH has not been used commercially and may provide an increase in level of partial resistance in future tobacco varieties. }, number={2}, journal={PLANT DISEASE}, author={McCorkle, Kestrel and Lewis, Ramsey and Shew, David}, year={2013}, month={Feb}, pages={252–258} }
 @article{cheng_booker_tu_burkey_zhou_shew_rufty_hu_2012, title={Arbuscular Mycorrhizal Fungi Increase Organic Carbon Decomposition Under Elevated CO2}, volume={337}, ISSN={["1095-9203"]}, DOI={10.1126/science.1224304}, abstractNote={A Fungal Culprit to Carbon Loss}, number={6098}, journal={SCIENCE}, author={Cheng, Lei and Booker, Fitzgerald L. and Tu, Cong and Burkey, Kent O. and Zhou, Lishi and Shew, H. David and Rufty, Thomas W. and Hu, Shuijin}, year={2012}, month={Aug}, pages={1084–1087} }
 @article{taylor_pasche_shew_lannon_gudmestad_2012, title={Tuber Rot of Potato Caused by Phytophthora nicotianae: Isolate Aggressiveness and Cultivar Susceptibility}, volume={96}, ISSN={["0191-2917"]}, DOI={10.1094/pdis-01-11-0037}, abstractNote={ A study was undertaken in 2008 and 2009 to examine potato (Solanum tuberosum) cultivar susceptibility, the potential of other host species to act as sources of inoculum for potato infections, and other aspects of potato–Phytophthora nicotianae interactions. Twelve isolates of P. nicotianae collected from five leaf, one petiole, and six tuber infections of potato from five states, as well as isolates from a variety of other host species, were evaluated for ability to cause tuber rot of potato via inoculation studies. Additionally, the susceptibility of 27 potato cultivars commonly grown in the United States to tuber infection by P. nicotianae was determined. Eighty-three percent of the isolates recovered from potato were highly aggressive, infecting tubers at nearly four times greater incidences than isolates originating from nonpotato hosts. With the exception of two tobacco isolates, zoospores of all isolates recovered from nonpotato hosts were able to infect potato tubers. Russet cultivars were significantly less susceptible to P. nicotianae than red and white cultivars in 2008, and red cultivars in 2009. Umatilla Russet was the most resistant cultivar in both years, whereas Red Norland and Dakota Rose were the most susceptible in both years. Results of a survey for P. nicotianae conducted in four states from 2008 through 2010 confirmed previous observations of naturally occurring infections of potato in Missouri, Nebraska, and Texas, as well as infections of potato in Michigan (documented for the first time). All isolates recovered in the survey were sensitive to mefenoxam (EC50 < 1.0 μg/ml). }, number={5}, journal={PLANT DISEASE}, author={Taylor, Raymond J. and Pasche, Julie S. and Shew, H. David and Lannon, K. R. and Gudmestad, Neil C.}, year={2012}, month={May}, pages={693–704} }
 @article{nifong_nicholson_shew_lewis_2011, title={Variability for Resistance to Phytophthora nicotianae Within a Collection of Nicotiana rustica Accessions}, volume={95}, ISSN={["1943-7692"]}, DOI={10.1094/pdis-11-10-0862}, abstractNote={ Black shank, caused by Phytophthora nicotianae, is one of the most important diseases affecting tobacco (Nicotiana tabacum) production worldwide. Many current tobacco cultivars possess immunity to race 0 of this pathogen conferred by introgressed dominant genetic factors. Novel alleles conditioning resistance to alternative races are desired. The objective of this research was to evaluate variability for black shank resistance within a collection of N. rustica germplasm using both soilborne disease nurseries and controlled race-specific (race 0 and race 1) inoculations. Nearly all of the 86 accessions studied exhibited very high resistance to race 0, and many displayed levels of race 1 resistance greater than that exhibited by the resistant flue-cured tobacco check, ‘K 346’. Materials found to be highly resistant to race 0 and race 1 in growth-chamber experiments also had the best survivability in field disease nurseries. N. rustica accessions TR 6, TR 12, TR 16, TR 21, TR 20, TR 48, TR 54, TR 57, and TR 69 could be sources of novel alleles with large effects on black shank resistance, and could have value for burley and flue-cured tobacco breeding. }, number={11}, journal={PLANT DISEASE}, author={Nifong, J. M. and Nicholson, J. S. and Shew, H. D. and Lewis, R. S.}, year={2011}, month={Nov}, pages={1443–1447} }
 @article{sullivan_parks_cubeta_gallup_melton_moyer_shew_2010, title={An Assessment of the Genetic Diversity in a Field Population of Phytophthora nicotianae with a Changing Race Structure}, volume={94}, ISSN={["1943-7692"]}, DOI={10.1094/pdis-94-4-0455}, abstractNote={ One hundred fifty-three isolates of Phytophthora nicotianae that were collected over a 4-year period from a single field were subjected to amplified fragment length polymorphism (AFLP) analysis to investigate the effect of different types of resistance in tobacco (Nicotiana tabacum) on genetic diversity in the pathogen population. No race 1 isolates were detected in the field prior to initiating the study, but the race was present in multiple plots by the end of the 4-year period. There were 102 race 0 isolates and 51 race 1 isolates characterized. Seventy-six of the 153 isolates had a unique AFLP profile, whereas the remaining 77 isolates were represented by 27 AFLP profiles shared by at least two isolates. Isolates of both races were found in both the unique and shared AFLP profile groups. Twenty-three of the AFLP profiles were detected in multiple years, indicating a clonal component to the pathogen population. Race 1 isolates that were detected over multiple years were always obtained from the same plot. No race 1 profile was found in more than one plot, confirming the hypothesis that the multiple occurrences of the race throughout the field were the result of independent events and not pathogen spread. Three identical race 0 AFLP profiles occurred in noncontiguous plots, and in each case, the plots contained the same partially resistant variety. Cluster analysis provided a high level of bootstrap support for 41 isolates in 19 clusters that grouped primarily by race and rotation treatment. Estimates of genetic diversity ranged from 0.365 to 0.831 and varied depending on tobacco cultivar planted and race. When averaged over all treatments, diversity in race 1 isolates was lower than in race 0 isolates at the end of each season. Deployment of single-gene resistance initially decreased genetic diversity of the population, but the diversity increased each year, indicating the pathogen was adapting to the host genotypes deployed in the field. }, number={4}, journal={PLANT DISEASE}, author={Sullivan, M. J. and Parks, E. J. and Cubeta, M. A. and Gallup, C. A. and Melton, T. A. and Moyer, J. W. and Shew, H. D.}, year={2010}, month={Apr}, pages={455–460} }
 @article{gallup_shew_2010, title={Occurrence of Race 3 of Phytophthora nicotianae in North Carolina, the Causal Agent of Black Shank of Tobacco}, volume={94}, ISSN={["0191-2917"]}, DOI={10.1094/pdis-94-5-0557}, abstractNote={ Black shank, caused by the oomycete Phytophthora nicotianae, causes significant annual yield losses in tobacco. Race 3 of P. nicotianae is reported here for the first time from North Carolina. It was identified from a North Carolina tobacco field with a history of tobacco varieties with Phl gene resistance and numerous field sites with no known deployment of varieties with the Phl gene. Race 3 was originally described from cigar-wrapper tobacco in Connecticut in the 1970s, but has not been reported in any other location since. Race 3 was defined as overcoming the Phl gene from Nicotiana longiflora but not the Php gene from N. plumbaginifolia. Stem and root inoculations were conducted on a set of host differentials to determine the virulence of North Carolina isolates. Stem inoculation was unable to distinguish between races 0 and 3 of P. nicotianae and is not a reliable method of identifying these virulence types. Race 1 gave a unique phenotype using stem inoculation. Root inoculation was the only reliable means of distinguishing between races 0 and 3. This is the first report of race 3 in North Carolina and the first report of damage to seedlings from root inoculations and to plants containing the Phl gene in naturally infested soil. }, number={5}, journal={PLANT DISEASE}, author={Gallup, C. A. and Shew, H. D.}, year={2010}, month={May}, pages={557–562} }
 @article{taylor_pasche_gallup_shew_gudmestad_2008, title={A foliar blight and tuber rot of potato caused by Phytophthora nicotianae: New occurrences and characterization of isolates}, volume={92}, ISSN={["0191-2917"]}, DOI={10.1094/pdis-92-4-0492}, abstractNote={ Phytophthora spp. are pathogenic to many plant species worldwide, and late blight, caused by Phytophthora infestans, and pink rot, caused by P. erythroseptica, are two important diseases of potato. Another Phytophthora sp., P. nicotianae, was recovered from pink-rot-symptomatic tubers collected from commercial fields in Nebraska, Florida, and Missouri in 2005, 2006, and 2007, respectively. P. nicotianae also was recovered from foliage obtained from commercial potato fields in Nebraska and Texas exhibiting symptoms very similar to those of late blight. Isolates of P. cactorum also were recovered from foliar infections in a commercial potato field in Minnesota in 2005. Natural infection of potato foliage by P. cactorum and infection of wounded potato tuber tissue via inoculation with zoospores of P. capsici are reported here for the first time. Isolates of P. nicotianae, regardless of origin, were primarily of the A1 mating type. All isolates of P. nicotianae and P. cactorum were sensitive to the fungicide mefenoxam. Optimum growth of P. nicotianae, P. erythroseptica, and P. cactorum in vitro occurred at 25°C; however, only P. nicotianae sustained growth at 35°C. Regardless of the tissue of origin, all isolates of P. nicotianae and P. cactorum were capable of infecting potato tubers and leaves. However, isolates of P. nicotianae were less aggressive than P. erythroseptica isolates only when tubers were not wounded prior to inoculation. Pink rot incidence varied significantly among potato cultivars following inoculation of nonwounded tubers with zoospores of P. nicotianae, ranging from 51% in Red Norland to 19% in Atlantic. Phytophthora spp. also differed significantly in their ability to infect potato leaves. Highest infection frequencies were obtained with P. infestans and levels of infection varied significantly among P. nicotianae isolates. The rate of foliar lesion expansion was similar among isolates of P. nicotianae and P. infestans. Whereas P. infestans infections yielded profuse sporulation, no sporulation was observed with foliar infections of P. nicotianae. }, number={4}, journal={PLANT DISEASE}, author={Taylor, Raymond J. and Pasche, Julie S. and Gallup, Courtney A. and Shew, H. David and Gudmestad, Neil C.}, year={2008}, month={Apr}, pages={492–503} }
 @article{elliott_lewis_shew_gutierrez_nicholson_2008, title={Evaluation of tobacco germplasm for seedling resistance to stem rot and target spot caused by Thanatephorus cucumeris}, volume={92}, ISSN={["0191-2917"]}, DOI={10.1094/PDIS-92-3-0425}, abstractNote={ Stem rot and target spot of tobacco, caused by Rhizoctonia solani and its teleomorph Thanatephorus cucumeris, respectively, can cause serious problems in production of tobacco (Nicotiana tabacum) seedlings. Previous screens for genetic resistance in tobacco have been limited. The objective of this study was to evaluate 97 genotypes composing several classes of tobacco and related Nicotiana spp. for seedling resistance to stem rot and target spot. Significant differences in disease incidence initially were observed among the genotypes for both stem rot and target spot; however, resistance to target spot was not observed when disease pressure was high. Partial resistance to stem rot was observed in several genotypes in repeated tests. These accessions may be useful as a source of resistance to R. solani in future breeding efforts. }, number={3}, journal={PLANT DISEASE}, author={Elliott, P. E. and Lewis, R. S. and Shew, H. D. and Gutierrez, W. A. and Nicholson, J. S.}, year={2008}, month={Mar}, pages={425–430} }
 @article{dong_shew_tredway_lu_sivamani_miller_qu_2008, title={Expression of the bacteriophage T4 lysozyme gene in tall fescue confers resistance to gray leaf spot and brown patch diseases}, volume={17}, ISSN={["1573-9368"]}, DOI={10.1007/s11248-007-9073-3}, abstractNote={Tall fescue (Festuca arundinacea Schreb.) is an important turf and forage grass species worldwide. Fungal diseases present a major limitation in the maintenance of tall fescue lawns, landscapes, and forage fields. Two severe fungal diseases of tall fescue are brown patch, caused by Rhizoctonia solani, and gray leaf spot, caused by Magnaporthe grisea. These diseases are often major problems of other turfgrass species as well. In efforts to obtain tall fescue plants resistant to these diseases, we introduced the bacteriophage T4 lysozyme gene into tall fescue through Agrobacterium-mediated genetic transformation. In replicated experiments under controlled environments conducive to disease development, 6 of 13 transgenic events showed high resistance to inoculation of a mixture of two M. grisea isolates from tall fescue. Three of these six resistant plants also displayed significant resistance to an R. solani isolate from tall fescue. Thus, we have demonstrated that the bacteriophage T4 lysozyme gene confers resistance to both gray leaf spot and brown patch diseases in transgenic tall fescue plants. The gene may have wide applications in engineered fungal disease resistance in various crops.}, number={1}, journal={TRANSGENIC RESEARCH}, author={Dong, Shujie and Shew, H. David and Tredway, Lane P. and Lu, Jianli and Sivamani, Elumalai and Miller, Eric S. and Qu, Rongda}, year={2008}, month={Feb}, pages={47–57} }
 @article{ceresini_shew_james_vilgalys_cubeta_2007, title={Phylogeography of the Solanaceae-infecting Basidiomycota fungus Rhizoctonia solani AG-3 based on sequence analysis of two nuclear DNA loci}, volume={7}, ISSN={1471-2148}, url={http://dx.doi.org/10.1186/1471-2148-7-163}, DOI={10.1186/1471-2148-7-163}, abstractNote={The soil fungus Rhizoctonia solani anastomosis group 3 (AG-3) is an important pathogen of cultivated plants in the family Solanaceae. Isolates of R. solani AG-3 are taxonomically related based on the composition of cellular fatty acids, phylogenetic analysis of nuclear ribosomal DNA (rDNA) and beta-tubulin gene sequences, and somatic hyphal interactions. Despite the close genetic relationship among isolates of R. solani AG-3, field populations from potato and tobacco exhibit comparative differences in their disease biology, dispersal ecology, host specialization, genetic diversity and population structure. However, little information is available on how field populations of R. solani AG-3 on potato and tobacco are shaped by population genetic processes. In this study, two field populations of R. solani AG-3 from potato in North Carolina (NC) and the Northern USA; and two field populations from tobacco in NC and Southern Brazil were examined using sequence analysis of two cloned regions of nuclear DNA (pP42F and pP89).Populations of R. solani AG-3 from potato were genetically diverse with a high frequency of heterozygosity, while limited or no genetic diversity was observed within the highly homozygous tobacco populations from NC and Brazil. Except for one isolate (TBR24), all NC and Brazilian isolates from tobacco shared the same alleles. No alleles were shared between potato and tobacco populations of R. solani AG-3, indicating no gene flow between them. To infer historical events that influenced current geographical patterns observed for populations of R. solani AG-3 from potato, we performed an analysis of molecular variance (AMOVA) and a nested clade analysis (NCA). Population differentiation was detected for locus pP89 (Phi ST = 0.257, significant at P < 0.05) but not for locus pP42F (Phi ST = 0.034, not significant). Results based on NCA of the pP89 locus suggest that historical restricted gene flow is a plausible explanation for the geographical association of clades. Coalescent-based simulations of genealogical relationships between populations of R. solani AG-3 from potato and tobacco were used to estimate the amount and directionality of historical migration patterns in time, and the ages of mutations of populations. Low rates of historical movement of genes were observed between the potato and tobacco populations of R. solani AG-3.The two sisters populations of the basidiomycete fungus R. solani AG-3 from potato and tobacco represent two genetically distinct and historically divergent lineages that have probably evolved within the range of their particular related Solanaceae hosts as sympatric species.}, number={1}, journal={BMC Evolutionary Biology}, publisher={Springer Science and Business Media LLC}, author={Ceresini, Paulo C and Shew, H David and James, Timothy Y and Vilgalys, Rytas J and Cubeta, Marc A}, year={2007}, pages={163} }
 @article{dong_tredway_shew_wang_sivamani_qu_2007, title={Resistance of transgenic tall fescue to two major fungal diseases}, volume={173}, ISSN={["0168-9452"]}, DOI={10.1016/j.plantsci.2007.08.002}, abstractNote={Tall fescue (Festuca arundinacea Schreb.) is an open-pollinated, perennial, cool-season turf and forage grass species of great economic importance. The main problems of maintenance of tall fescue, and many other turfgrasses, are two severe fungal diseases: gray leaf spot caused by Magnaporthe grisea, and brown patch caused by Rhizoctonia solani. Three genes from various sources have been introduced into two elite cultivars, ‘Coronado’ and ‘Matador’, of tall fescue through Agrobacterium-mediated transformation, and conferred resistance to the diseases. Two genes, the alfalfa β-1,3-glucanase AGLU1 gene and a truncated frog dermaseptin SI gene, conferred resistance to both diseases. The rice Pi9 gene was specific against gray leaf spot. Of 15 T0 transgenic plants examined, 6 showed high levels of resistance to M. grisea, and 3 had enhanced resistance to R. solani. The resistance in most of these cases was highly significant.}, number={5}, journal={PLANT SCIENCE}, author={Dong, Shujie and Tredway, Lane P. and Shew, H. David and Wang, Guo-Liang and Sivamani, Elumalai and Qu, Rongda}, year={2007}, month={Nov}, pages={501–509} }
 @article{fichtner_hesterberg_smyth_shew_2006, title={Differential sensitivity of Phytophthora parasitica var. nicotianae and Thielaviopsis basicola to monomeric aluminum species}, volume={96}, ISBN={0031-949X}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-33644892775&partnerID=MN8TOARS}, DOI={10.1094/phyto-96-0212}, abstractNote={ Aluminum (Al) is toxic to many plant pathogens, including Thielaviopsis basicola and Phytophthora parasitica var. nicotianae. Because fungi-toxicity of Al has been described in soils over a wide pH range, multiple species of Al may be responsible for pathogen suppression. The goals of this work were to determine the sensitivity of T. basicola and P. para-sitica var. nicotianae to Al over a range of pH values, quantify the toxicity of monomeric Al species to production of sporangia of P. parasitica var. nicotianae and chlamydospores of T. basicola, and detect the accumulation of Al in pathogen structures. A complete factorial treatment design was used with Al levels ranging from 0 to 100 μM and pH levels ranging from 4 to 6 in a minimal salts medium. The chemistry of test solutions was modeled using GEOCHEM-PC. Colonies were grown in 5% carrot broth, and after 1 or 2 days, the nutrient solution was removed, colonies were rinsed with water, and Al test solutions were added to each of four replicate plates. After 2 days, propagules were counted and colonies were stained with the Al-specific, fluorescent stain lumogallion. The oomycete P. parasitica var. nicotianae was sensitive to multiple monomeric Al species, whereas sensitivity of T. basicola to Al was pH-dependent, suggesting that only Al3+ is responsible for suppression of this fungal pathogen. Chlamydospore production by T. basicola was inhibited at pH values <5.0 and Al levels >20 μM, whereas sporangia production by P. parasitica was inhibited at Al levels as low as 2 μM across all pH values tested. The lumogallion stain was an effective technique for detection of Al in fungal tissues. Aluminum accumulated in sporangia and zoospores of P. parasitica var. nicotianae and in nonmelanized chlamy-dospores of T. basicola, but not in cell walls of either organism. The differential sensitivity of the two organisms may indicate that true fungi respond differently to Al than members of the oomycota, which are more closely related to plants. }, number={3}, journal={Phytopathology}, author={Fichtner, E. J. and Hesterberg, Dean and Smyth, T. J. and Shew, H. D.}, year={2006}, pages={212} }
 @article{sullivan_melton_shew_2005, title={Fitness of races 0 and 1 of Phytophthora parasitica var. nicotianae}, volume={89}, ISSN={["0191-2917"]}, DOI={10.1094/PD-89-1220}, abstractNote={ Deployment of tobacco (Nicotiana tabacum) varieties with complete resistance to race 0 of Phytophthora parasitica var. nicotianae has led to a rapid increase in the field populations of race 1 in North Carolina. In a field study, population levels of race 1 decreased relative to race 0 when cultivars with partial resistance to both races were planted, suggesting that race 1 isolates were less fit than race 0 isolates. Experiments were conducted to quantify differences in aggressiveness and survivability of the two races. Tobacco varieties with low, moderate, or high levels of partial resistance were inoculated with 60 pathogen isolates, and symptom development was monitored for 3 weeks. Race 0 isolates were more aggressive than race 1 isolates on cultivars with moderate or high levels of partial resistance; incubation periods were shorter and root rot severity was greater with race 0 isolates. Isolates of race 1, however, caused greater stunting of plants with moderate and high levels of partial resistance than race 0 isolates. Field microplots were infested with either a single race or an equal mixture of each race. Soil samples were collected at the end of two growing seasons and again the following spring. Pathogen populations declined from 40 to 80% during winter months, but population declines for race 0 were lower than for race 1 in each treatment over each winter. Race shifts from race 1 to race 0 that were observed in the presence of cultivars with partial resistance appear to be primarily the result of differences in aggressiveness of the races, with a possible minor effect of enhanced overwintering survival of race 0 compared with race 1. }, number={11}, journal={PLANT DISEASE}, author={Sullivan, MJ and Melton, TA and Shew, HD}, year={2005}, month={Nov}, pages={1220–1228} }
 @article{sullivan_melton_shew_2005, title={Managing the race structure of Phytophthora parasitica var. nicotianae with cultivar rotation}, volume={89}, ISSN={["0191-2917"]}, DOI={10.1094/PD-89-1285}, abstractNote={ Deployment of tobacco cultivars with single-gene, complete resistance to race 0 of the tobacco black shank pathogen, Phytophthora parasitica var. nicotianae, has resulted in a rapid increase in the occurrence of race 1 of the pathogen in North Carolina. Cultivar-rotation studies were conducted in three fields to assess how different levels and types of resistance affected the race structure and population dynamics of the pathogen when deployed in fields initially containing single or mixed races of the pathogen. In a field with both races present, a high level of partial resistance in cv. K 346 was most effective in reducing disease and decreasing the proportion of race 1 in the pathogen population. The deployment of complete resistance in cv. NC 71 resulted in intermediate levels of disease control and race 1 became the predominate race. The cv. K 326, with a low level of partial resistance, had the highest levels of disease, and race 0 was the dominant race recovered. In a field where no race 1 was detected initially, disease incidence was high with the use of partial resistance. Complete resistance was very effective in suppressing disease, but race 1 was recovered after only one growing season. By the end of the third growing season, race 1 was recovered from most treatments where single-gene resistance was deployed. A high level of partial resistance was most effective in suppressing disease in a field where race 1 initially was the predominant race. A rotation between cultivars with single-gene resistance and cultivars with a high level of partial resistance should provide the most effective approach to black shank management. This rotation will reduce disease incidence and minimize race shifts in the pathogen and, over time, should prolong the usefulness of the Ph gene for black shank control in commercial production of tobacco. }, number={12}, journal={PLANT DISEASE}, author={Sullivan, MJ and Melton, TA and Shew, HD}, year={2005}, month={Dec}, pages={1285–1294} }
 @article{fichtner_benson_diab_shew_2004, title={Abiotic and biological suppression of Phytophthora parasitica in a horticultural medium containing composted swine waste}, volume={94}, ISSN={["1943-7684"]}, DOI={10.1094/PHYTO.2004.94.7.780}, abstractNote={ Horticultural potting media have been amended with compost to enhance biological suppression and with Al2(SO4)3 to enhance abiotic suppression of plant pathogens, but these factors have not been simultaneously incorporated into the same medium. In this study, the efficacy of aluminum (Al)-amended potting medium containing 20% composted swine waste (CSW) was assessed for control of Phytophthora parasitica (syn. P. nicotianae), a soilborne pathogen causing damping-off of many horticultural bedding plants. Steamed and unsteamed media were amended with no Al or Al at 0.0079 g of Al g-1 of medium with an Al2(SO4)3 solution at either pH 4 or pH 6. Infested leaf disks were buried for 2-day durations beginning 0, 6, 13, and 21 days after Al amendment. The number of sporangia produced on infested leaf disks was assessed. A similar experiment was conducted to determine the effect of steaming and Al amendments on pathogen populations. Medium treated with the pH 4 solution consistently reduced sporangia production between 38 and 65% on day 0, but no Al effect was noted at subsequent time points. The pH 6 amendment did not consistently affect sporangia production. Exchangeable Al levels decreased over time, and abiotic suppression was only observed at >2 μM Al g-1 of medium. Pathogen populations were occasionally affected by steaming and Al. Sporangia production in unsteamed medium was reduced by 50% on leaf disks buried on days 6, 13, and 21, but not on day 0. Al amendment of a 20% CSW potting medium enhanced suppression of P. parasitica and abiotic suppression occurred before biological suppression developed. }, number={7}, journal={PHYTOPATHOLOGY}, author={Fichtner, EJ and Benson, DM and Diab, HG and Shew, HD}, year={2004}, month={Jul}, pages={780–788} }
 @article{uriarte_shew_bowman_2004, title={Effect of soluble silica on brown patch and dollar spot of creeping bentgrass}, volume={27}, ISSN={["1532-4087"]}, DOI={10.1081/PLN-120027657}, abstractNote={Abstract Disease pressure on cool season turfgrasses is very high in the transition zone due to the heat and humidity of prolonged summers. Creeping bentgrass (Agrostis stolonifera L.) is susceptible to both brown patch (Rhizoctonia solani Kuhn) and dollar spot (Sclerotinia homoeocarpa F.T. Bennett) fungi. The objective of this study was to assess the potential of soluble silica for reducing the severity or incidence of disease on creeping bentgrass. Two mature stands of creeping bentgrass, maintained as putting greens, were used. Both greens were constructed to USGA specifications and planted with either “Penncross” or “Cato” and “Crenshaw” blend creeping bentgrass. Plots were treated biweekly with silica at rates of 0, 25, and 50 kg ha−1. Turf quality was unaffected by silica application. Differences in disease incidence between the silica treatments and the control were observed in 1995 but not in 1996. There was no effect of treatment on tissue Si, suggesting that creeping bentgrass may be a Si excluder. Based on these results, silica may provide some degree of protection from dollar spot and brown patch. However, the level of control is unlikely to satisfy expectations for putting green turf quality.}, number={2}, journal={JOURNAL OF PLANT NUTRITION}, author={Uriarte, RF and Shew, HD and Bowman, DC}, year={2004}, pages={325–339} }
 @article{ceresini_shew_vilgalys_gale_cubeta_2003, title={Detecting migrants in populations of Rhizoctonia solani anastomosis group 3 from potato in North Carolina using multilocus genotype probabilities}, volume={93}, ISSN={["1943-7684"]}, DOI={10.1094/PHYTO.2003.93.5.610}, abstractNote={ The relative contribution of migration of Rhizoctonia solani anastomosis group 3 (AG-3) on infested potato seed tubers originating from production areas in Canada, Maine, and Wisconsin (source population) to the genetic diversity and structure of populations of R. solani AG-3 in North Carolina (NC) soil (recipient population) was examined. The frequency of alleles detected by multilocus polymerase chain reaction-restriction fragment length polymorphisms, heterozygosity at individual loci, and gametic phase disequilibrium between all pairs of loci were determined for subpopulations of R. solani AG-3 from eight sources of potato seed tubers and from five soils in NC. Analysis of molecular variation revealed little variation between seed source and NC recipient soil populations or between subpopulations within each region. Analysis of population data with a Bayesian-based statistical method previously developed for detecting migration in human populations suggested that six multilocus genotypes from the NC soil population had a statistically significant probability of being migrants from the northern source population. The one-way (unidirectional) migration of genotypes of R. solani AG-3 into NC on infested potato seed tubers from Canada, Maine, and Wisconsin provides a plausible explanation for the lack of genetic subdivision (differentiation) between populations of the pathogen in NC soils or between the northern source and the NC recipient soil populations. }, number={5}, journal={PHYTOPATHOLOGY}, author={Ceresini, PC and Shew, HD and Vilgalys, RJ and Gale, LR and Cubeta, MA}, year={2003}, month={May}, pages={610–615} }
 @article{ceresini_shew_vilgalys_cubeta_2002, title={Genetic diversity of Rhizoctonia solani AG-3 from potato and tobacco in North Carolina}, volume={94}, ISSN={["0027-5514"]}, DOI={10.2307/3761778}, abstractNote={Anastomosis group 3 (AG-3) of Rhizoctonia solani (teleomorph = Thanatephorus cucumeris) is frequently associated with diseases of potato (AG-3 PT) and tobacco (AG-3 TB). Although isolates of R. solani AG-3 from these two Solanaceous hosts are somatically related based on anastomosis reaction and taxonomically related based on fatty acid, isozyme and DNA characters, considerable differences are evident in their biology, ecology, and epidemiology. However, genetic diversity among field populations of R. solani AG-3 PT and TB has not been documented. In this study, the genetic diversity of field populations of R. solani AG-3 PT and AG-3 TB in North Carolina was examined using somatic compatibility and amplified fragment length polymorphism (AFLP) criteria. A sample of 32 isolates from potato and 36 isolates from tobacco were paired in all possible combinations on PDA plus activated charcoal and examined for their resulting somatic interactions. Twenty-eight and eight distinct somatic compatibility groups (SCG) were identified in the AG-3 PT and AG-3 TB samples, respectively. AFLP analyses indicated that each of the 32 AG-3 PT isolates had a distinct AFLP phenotype, whereas 28 AFLP phenotypes were found among the 36 isolates of AG-3 TB. None of the AG-3 PT isolates were somatically compatible or shared a common AFLP phenotype with any AG-3 TB isolate. Clones (i.e., cases where two or more isolates were somatically compatible and shared the same AFLP phenotype) were identified only in the AG-3 TB population. Four clones from tobacco represented 22% of the total population. All eight SCG from tobacco were associated with more than one AFLP phenotype. Compatible somatic interactions between AG-3 PT isolates occurred only between certain isolates from the same field (two isolates in each of four different fields), and when this occurred AFLP phenotypes were similar but not identical.}, number={3}, journal={MYCOLOGIA}, author={Ceresini, PC and Shew, HD and Vilgalys, RJ and Cubeta, MA}, year={2002}, pages={437–449} }
 @article{ceresini_shew_vilgalys_rosewich_cubeta_2002, title={Genetic structure of populations of Rhizoctonia solani AG-3 on potato in eastern North Carolina}, volume={94}, ISSN={["0027-5514"]}, DOI={10.2307/3761779}, abstractNote={A polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method was developed to identify and differentiate genotypes of Rhizoctonia solani anastomosis group 3 subgroup PT (AG-3 PT), a fungal pathogen of potato. Polymorphic co-dominant single-locus PCR-RFLP markers were identified after sequencing of clones from a genomic library and digestion with restriction enzymes. Multilocus genotypes were determined by a combination of PCR product and digestion with a specific restriction enzyme for each of seven loci. A sample of 104 isolates from one commercial field in each of five counties in eastern North Carolina was analyzed, and evidence for high levels of gene flow between populations was revealed. When data were clone-corrected and samples pooled into one single North Carolina population, random associations of alleles were found for all loci or pairs of loci, indicating random mating. However, when all genotypes were analyzed, the observed genotypic diversity deviated from panmixia and alleles within and between loci were not randomly associated. These findings support a model of population structure for R. solani AG-3 PT on potato that includes both recombination and clonality.}, number={3}, journal={MYCOLOGIA}, author={Ceresini, PC and Shew, HD and Vilgalys, RJ and Rosewich, UL and Cubeta, MA}, year={2002}, pages={450–460} }
 @article{johnson_wolff_wernsman_atchely_shew_2002, title={Origin of the black shank resistance gene, Ph, in tobacco cultivar Coker 371-gold}, volume={86}, ISSN={["0191-2917"]}, DOI={10.1094/PDIS.2002.86.10.1080}, abstractNote={ Flue-cured tobacco (Nicotiana tabacum) cultivar Coker 371-Gold (C 371-G) possesses a dominant gene, Ph, that confers high resistance to black shank disease, caused by race 0 of the soil-borne pathogen Phytophthora parasitica var. nicotianae. The origin of this gene is unknown. Breeding lines homozygous for the Ph gene were hybridized with NC 1071 and L8, flue-cured and burley genotypes known to possess qualitative resistance genes from Nicotiana plumbaginifolia and N. longiflora, respectively. The F1 hybrids were out-crossed to susceptible testers and the progenies evaluated in field black shank nurseries and in greenhouse disease tests with P. parasitica var. nicotianae race 0. Results showed that Ph was allelic to Php from N. plumbaginifolia in NC 1071. Testcross populations of hybrids between burley lines homozygous for Ph and L8, possessing Phl from N. longiflora, showed that Ph and Phl integrated into the same tobacco chromosome during interspecific transfer. Nevertheless, the two loci were estimated to be 3 cM apart. Random amplified polymorphic DNA (RAPD) analyses of the testcross progenies confirmed that recombination between the two loci was occurring. Forty-eight RAPD markers linked to Ph in doubled haploid lines were used in cluster analyses with multiple accessions of N. longiflora and N. plumbaginifolia, breeding lines L8, NC 1071, and DH92-2770-40, and cultivars K 326, Hicks, and C 371-G. A cladogram or region tree confirmed the data obtained from field and greenhouse trials, that Ph, transferred from C 371-G to DH92-2770-40, and Php in NC 1071 were allelic and originated from N. plumbaginifolia. }, number={10}, journal={PLANT DISEASE}, author={Johnson, ES and Wolff, MF and Wernsman, EA and Atchely, WR and Shew, HD}, year={2002}, month={Oct}, pages={1080–1084} }
 @inbook{shew_2001, title={Direct penetration}, booktitle={Encyclopedia of plant pathology: Vol. 1}, publisher={New York: John Wiley and Sons, Inc.}, author={Shew, H. D.}, editor={O. C. Maloy and Murray, T. D.Editors}, year={2001}, pages={311–312} }
 @article{harrison_shew_2001, title={Effects of soil pH and nitrogen fertility on the population dynamics of Thielaviopsis basicola}, volume={228}, ISSN={["1573-5036"]}, DOI={10.1023/A:1004845715885}, number={2}, journal={PLANT AND SOIL}, author={Harrison, UJ and Shew, HD}, year={2001}, month={Jan}, pages={147–155} }
 @inbook{shew_2001, title={Indirect penetration}, booktitle={Encyclopedia of plant pathology: Vol. 1}, publisher={New York: John Wiley and Sons, Inc.}, author={Shew, H. D.}, editor={O. C. Maloy and Murray, T. D.Editors}, year={2001}, pages={571} }
 @inbook{shew_2001, title={Infection}, booktitle={Encyclopedia of plant pathology: Vol. 1}, publisher={New York: John Wiley and Sons, Inc.}, author={Shew, H. D.}, editor={O. C. Maloy and Murray, T. D.Editors}, year={2001}, pages={572–574} }
 @inbook{shew_2001, title={Infection courts}, booktitle={Encyclopedia of plant pathology: Vol. 1}, publisher={New York: John Wiley and Sons, Inc.}, author={Shew, H. D.}, editor={O. C. Maloy and Murray, T. D.Editors}, year={2001}, pages={574–575} }
 @article{fichtner_hesterberg_shew_2001, title={Nonphytotoxic aluminum-peat complexes suppress Phytophthora parasitica}, volume={91}, ISSN={["1943-7684"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0035156475&partnerID=MN8TOARS}, DOI={10.1094/PHYTO.2001.91.11.1092}, abstractNote={ Amendment of peat-based potting media with Al2(SO4)3 suppresses damping-off of Vinca (Catharanthus roseus) caused by Phytophthora parasitica. The species of aluminum (Al) responsible for disease suppression have not been identified. The objective of this study was to determine the effects of amount and pH of Al2(SO4)3 amendment solutions on survival of P. parasitica. In separate experiments, peat was amended with Al2(SO4)3 solutions adjusted to pH 4 or 6 at either 0.0158 or 0.0079 g of Al per gram of peat. Amended peat was placed in Büchner funnels maintained at -2.5 kPa matric potential. Peat was infested with P. parasitica by placing zero, two, or five colonized Vinca leaf disks in each funnel, and 15 Vinca seeds were placed in each funnel. After 24 h, the matric potential was brought to 0 kPa to induce zoospore release and returned to -2.5 kPa after 24 h. Pathogen populations and stand counts were assessed after 2-week incubation. Al amendment solutions at both pH 4 and 6 reduced pathogen populations at 0.0158 g of Al per gram of peat. Solutions at pH 4 reduced pathogen populations by more than 90% at both inoculum levels; amendment solutions at pH 6 reduced populations by 95% at the low inoculum level and 65% at the high inoculum level. The prevalence of Al(OH)2+ in peat amended with Al2(SO4)3 solution at pH 6 suggests that ions other than Al3+ may be responsible for pathogen suppression. Based on the difference in chemical conditions of Al-amended peat and suppressive mineral soils, the mechanism of Al-mediated suppression of plant pathogens is speculated to be different in the two systems. Peat containing Al-peat complexes was chemically suppressive to P. parasitica and may confer Al-mediated suppression of plant pathogens with a nonphytotoxic form of Al. }, number={11}, journal={PHYTOPATHOLOGY}, author={Fichtner, EJ and Hesterberg, DL and Shew, HD}, year={2001}, month={Nov}, pages={1092–1097} }
 @inbook{shew_2001, title={Penetration}, booktitle={Encyclopedia of plant pathology: Vol. 1}, publisher={New York: John Wiley and Sons, Inc.}, author={Shew, H. D.}, editor={O. C. Maloy and Murray, T. D.Editors}, year={2001}, pages={747–748} }
 @article{hudyncia_shew_cody_cubeta_2000, title={Evaluation of wounds as a factor to infection of cabbage by ascospores of Sclerotinia sclerotiorum}, volume={84}, ISSN={["0191-2917"]}, DOI={10.1094/PDIS.2000.84.3.316}, abstractNote={ A semi-selective medium was used to examine the aerobiology of ascospores of Sclerotinia sclerotiorum in five commercial cabbage fields in eastern North Carolina. Ascospores were present in all five fields from 26 September to 30 November. However, numbers of ascospores varied greatly depending on location, sampling date, and time. In general, peak ascospore deposition occurred between 11:00 A.M. and 1:00 P.M., with the number of colonies recovered ranging from 3 to 55/dish (9 cm in diameter). Peak ascospore numbers at all locations were found from mid- to late October, but a second, smaller peak was also evident at each location in late November. Information obtained was employed to evaluate the role of wounding in infection of cabbage by ascospores of S. sclerotiorum in controlled environmental chambers. A method for production and release of ascospores of S. sclerotiorum was employed in controlled-environment chambers for the inoculation of cabbage plants with one of three representative foliar wounds: a bruise, a cut, or a non-lethal freeze. Wounding treatments were applied to 7-week-old cabbage plants, misting was added to maintain continuous leaf wetness, and ascospores were released from apothecia twice daily for four consecutive days. Spore trapping with a semi-selective medium indicated that inoculum was evenly distributed within the chambers and deposition was similar to levels recorded in the field. At 31 days after inoculation, disease incidence ranged from 0% on the control to 96% on the freeze treatments. Freeze-treated plants showed the highest disease severity throughout the entire incubation period. Mean area under the disease progress curve of severity values were 0, 0.2, 34 and 60 for the control, cut, bruise, and freeze treatments, respectively. Results indicate that freeze and bruise injuries are important factors associated with infection of cabbage by S. sclerotiorum. }, number={3}, journal={PLANT DISEASE}, author={Hudyncia, J and Shew, HD and Cody, BR and Cubeta, MA}, year={2000}, month={Mar}, pages={316–320} }
 @article{gutierrez_shew_2000, title={Factors that affect development of collar rot on tobacco seedlings grown in greenhouses}, volume={84}, ISSN={["1943-7692"]}, DOI={10.1094/PDIS.2000.84.10.1076}, abstractNote={ Collar rot, caused by Sclerotinia sclerotiorum, is an important disease of tobacco transplants produced under greenhouse conditions. Factors that affect the development of the disease were studied, including age of seedlings, presence of an external source of nutrients (leaf extract), clipping (leaf removal) practices, exposure to low temperature, and leaf injury caused by heat and a chemical. Flue-cured tobacco seedlings, cultivar K-326, were grown in polystyrene cell trays floating on a nutrient solution. Trays were maintained in a phytotron growth chamber with a 28/18°C day/night temperature regime. Seedlings were inoculated with ascospores of S. sclerotiorum at the desired stage of growth by placing mature apothecia in the growth chamber and inducing ascospore release and deposition. Disease incidence was determined by examining seedlings for the presence of stem lesions over the next 15 to 21days. Seedlings between 35 and 53 days old were more susceptible to collar rot than younger or older seedlings. Inoculum efficiency was highest and disease was most severe when an external source of nutrients was present on leaf surfaces. Clipping of leaf tips did not increase disease, but if the leaf pieces created by clipping were left on seedlings, collar rot development was enhanced compared with treatments where debris was removed. Heat and chemical injuries that resulted in necrotic tissue provided highly susceptible infection courts for ascospores of S. sclerotiorum, but exposure to low temperature, which caused no visible injury, did not enhance infection. Adoption of cultural practices that minimize accumulation of leaf debris and eliminate factors that cause necrotic injury on leaves should greatly reduce the severity of collar rot of tobacco seedlings. }, number={10}, journal={PLANT DISEASE}, author={Gutierrez, WA and Shew, HD}, year={2000}, month={Oct}, pages={1076–1080} }
 @article{gutierrez_shew_1998, title={Identification and quantification of ascospores as the primary inoculum for collar rot of greenhouse-produced tobacco seedlings}, volume={82}, ISSN={["0191-2917"]}, DOI={10.1094/PDIS.1998.82.5.485}, abstractNote={ Collar rot, caused by Sclerotinia sclerotiorum, is a severe disease of tobacco seedlings grown in greenhouses. A semiselective medium was adapted and used to detect the presence and quantity of ascospores in commercial greenhouses. Petri dishes of the semiselective medium were placed inside and outside of greenhouses in four counties during the transplant production period in 1995 and 1996. Ascospores were present throughout the production period each year (February to April) and were confirmed to be the primary inoculum for the disease. Significant differences were observed in the number of ascospores trapped within and between counties. Peak numbers of ascospores were trapped between 10 and 12 a.m., and higher numbers of ascospores were trapped outside than inside houses. In general, distribution of ascospores inside houses was uniform unless a high concentration of apothecia was present very close to one section of the greenhouse. The semiselective medium and trapping technique used in this study may allow development of a forecasting system for collar rot of tobacco based on the presence and level of pathogen inoculum. }, number={5}, journal={PLANT DISEASE}, author={Gutierrez, WA and Shew, HD}, year={1998}, month={May}, pages={485–490} }
 @article{carlson_wolff_shew_wernsman_1997, title={Inheritance of resistance to race 0 of Phytophthora parasitica var. nicotianae from the flue-cured tobacco cultivar Coker 371-Gold}, volume={81}, DOI={10.1094/PDIS.1997.81.11.1269}, abstractNote={ Black shank, caused by Phytophthora parasitica var. nicotianae, is a widespread and severe disease of tobacco throughout the southeastern United States. Partial resistance derived from the cigar tobacco cultivar Florida 301 has been the primary means of reducing losses to the disease for many years. The recently released tobacco cultivar, Coker 371-Gold (C 371-G), was found to provide an additional source of resistance to P. parasitica var. nicotianae. Although the resistance in C 371-G is being used widely by breeders, the origin and inheritance of this resistance mechanism was unknown. Two populations of doubled haploid lines derived from C 371-G were used to determine that C 371-G possesses a single, dominant gene designated Ph, which confers a very high level of resistance to race 0 of P. parasitica var. nicotianae. A greenhouse inoculation procedure was developed that provided an efficient means of screening for the presence of this resistance gene prior to selection in the field, and confirmed that Ph provides complete resistance to race 0 but no resistance to race 1 of P. parasitica var. nicotianae. Because Florida 301 resistance is effective against both races of the pathogen that occur in the major tobacco growing areas of the United States, combination of these two sources of resistance should provide enhanced protection of new tobacco cultivars to P. parasitica var. nicotianae. }, number={11}, journal={Plant Disease}, author={Carlson, S. R. and Wolff, M. F. and Shew, H. D. and Wernsman, E. A.}, year={1997}, pages={1269–1274} }
 @article{hood_shew_1997, title={Initial cellular interactions between Thielaviopsis basicola and tobacco root hairs}, volume={87}, ISSN={["0031-949X"]}, DOI={10.1094/PHYTO.1997.87.3.228}, abstractNote={Cellular events that occur during the initial interactions between Thielaviopsis basicola and root hairs of tobacco (Nicotiana tabacum) were examined microscopically. Time-course documentation of the infection process indicated a dynamic interaction between T. basicola and the living host cell. Upon root hair contact and recognition, the vegetative apex of T. basicola rapidly differentiated to form infection structures, and the host cell responded cytologically. Penetration was achieved by threadlike hyphae that subsequently developed distal swellings, and intracellular hyphae of sickle-shaped morphology advanced from the distal swelling and colonized the cell. Streaming of the host cytoplasm became aggregated near the infection site prior to penetration and accumulated around the infecting hyphae as long as the host cell was viable. Substantial callose deposition, in the form of a bell-shaped collar around infection structures, resulted from the cytological activity at the infection site. Penetration of dead root hairs was common, but did not lead to the development of infection structures or to a sustained association with the host tissue; T. basicola exited dead root hairs and resumed vegetative growth. The establishment of the parasitic relationship by T. basicola was characteristic of hemibiotrophic fungi in that, initially, biotrophic infection led to tissue colonization, and host cell survival was limited under parasitism.}, number={3}, journal={PHYTOPATHOLOGY}, author={Hood, ME and Shew, HD}, year={1997}, month={Mar}, pages={228–235} }
 @article{hood_shew_1997, title={Reassessment of the role of saprophytic activity in the ecology of Thielaviopsis basicola}, volume={87}, ISSN={["1943-7684"]}, DOI={10.1094/PHYTO.1997.87.12.1214}, abstractNote={ The ability of Thielaviopsis basicola to survive saprophytically in soil was investigated using root tissue from susceptible hosts as organic substrates. Inoculum densities were lower in soils amended with root tissue than in nonamended controls after 2 and 4 weeks of incubation. The greatest decrease occurred in soils containing the highest concentration of root tissue or in soils in which root tissue included the soluble components of the living root. Reproduction by T. basicola also was examined in axenic media containing either killed root pieces or various carbohydrates as the sole carbohydrate source. T. basicola utilized killed root tissue as a carbohydrate source in axenic media, particularly in cultures in which root tissue included the soluble components. Enzymatic activities of T. basicola, however, did not result in maceration of the root tissue. T. basicola utilized sucrose and cellobiose, but did not utilize structural carbohydrates such as cellulose, hemicellulose, or pectin. Based on the absence of significant saprophytic ability, T. basicola should be classified ecologically as an obligate parasite. }, number={12}, journal={PHYTOPATHOLOGY}, author={Hood, ME and Shew, HD}, year={1997}, month={Dec}, pages={1214–1219} }
 @article{gutierrez_shew_melton_1997, title={Sources of inoculum and management for Rhizoctonia solani damping-off on tobacco transplants under greenhouse conditions}, volume={81}, ISSN={["0191-2917"]}, DOI={10.1094/PDIS.1997.81.6.604}, abstractNote={ Damping-off and target spot are important diseases of tobacco transplants produced under greenhouse conditions. Identification of sources of inoculum for these diseases caused by Rhizoctonia solani is an important first step in disease management. Control strategies based on sanitation and the eradication of primary inoculum were studied. Potting mix and Styrofoam trays used in transplant production were assayed to determine if they were sources of primary inoculum. Eleven sources of potting mix were sampled over a 2-year period. None of the mixes contained viable inoculum of R. solani. R. solani was isolated from previously used trays after 1 year of storage by removing and plating pieces of Styrofoam from individual tray cells on alkaline water agar (AWA). Sclerotia and melanized hyphae of R. solani were observed in the cracks present in the cells of the trays. Dry heat (70 to 80°C for 2 h) and chemical (sodium hypochlorite and sodium chloride) treatments reduced the levels of inoculum on trays up to 45% compared to controls, but only methyl bromide and steam treatments (80°C for 0.5 to 2.0 h) eradicated inoculum of R. solani from trays. Elimination of primary inoculum from previously used trays effectively controlled target spot and stem rot diseases caused by R. solani. }, number={6}, journal={PLANT DISEASE}, author={Gutierrez, WA and Shew, HD and Melton, TA}, year={1997}, month={Jun}, pages={604–606} }
 @article{hood_shew_1997, title={The influence of nutrients on development, resting hyphae and aleuriospore induction of Thielaviopsis basicola}, volume={89}, ISSN={["1557-2536"]}, DOI={10.2307/3761136}, abstractNote={AbstractTwo isolates of Thielaviopsis basicola, one from tobacco and one from cotton, were grown in crude host root extracts at varied dilutions. Aspects of hyphal morphology including hyphal diameter, hyphal length, and degree of branching were positively correlated with the level of available nutrients under these conditions. Atypical hyphal forms were produced by T. basicola under conditions of nutrient stress, and these forms were similar to two cultural mutants previously reported. Secondary chlamydospores also were observed under nutrient stress conditions. Hyphal segments that possessed cytological and morphological features analogous to endoconidia and aleuriospores of T. basicola were observed during later stages of culture development under nutrient conditions favorable for growth and reproduction. These structures were termed “resting hyphae” because T. basicola grew from them upon restoration of nutrients when other regions of hyphae were no longer viable. Natural and simulated depletion of nutrients in the culture environment following a period of vegetative growth induced aleuriospore production. Development of aleuriospores under these culture conditions demonstrated that T. basicola is able to produce a substantial number of reproductive structures from nutrient reserves held within the existing thallus.Key Words: Chalara eleganschlamydosporehemibiotroph}, number={5}, journal={MYCOLOGIA}, author={Hood, ME and Shew, HD}, year={1997}, pages={793–800} }
 @article{shew_melton_1995, title={Target of spot of tobacco}, volume={79}, DOI={10.1094/pd-79-0005}, number={1}, journal={Plant Disease}, author={Shew, H. D. and Melton, T. A.}, year={1995}, pages={6} }
 @article{shew_shoemaker_1993, title={EFFECTS OF HOST-RESISTANCE AND SOIL FUMIGATION ON THIELAVIOPSIS-BASICOLA AND DEVELOPMENT OF BLACK ROOT-ROT ON BURLEY TOBACCO}, volume={77}, ISSN={["0191-2917"]}, DOI={10.1094/PD-77-1035}, abstractNote={Cultivars of burley tobacco (Nicotiana tabacum) with different levels of resistance to Thielaviopsis basicola were planted in fields naturally infested with the pathogen. Severity of black root rot and populations of T. basicola were determined at transplant, midseason, and after final harvest. Cultivars with monogenic resistance to T. basicola derived from Nicotiana debneyi developed little or no root rot in all tests and suppressed pathogen reproduction during the growing sermon. The severity of root rot and the reproduction of T. basicola were not related to the level of partial resistance}, number={10}, journal={PLANT DISEASE}, author={SHEW, HD and SHOEMAKER, PB}, year={1993}, month={Oct}, pages={1035–1039} }
 @article{shew_main_1990, title={INFECTION AND DEVELOPMENT OF TARGET SPOT OF FLUE-CURED TOBACCO CAUSED BY THANATEPHORUS-CUCUMERIS}, volume={74}, ISSN={["1943-7692"]}, DOI={10.1094/PD-74-1009}, abstractNote={The effects of misting frequency and temperature regime on basidiospore infection and lesion development of target spot of tobacco were determined. Three isolates of Thanatephorus cucumeris (Rhizoctonia solani AG-2-2) produced hymenia and basidiospores equally when exposed to moderate temperatures and extended periods of high relative humidity. Optimum temperatures for hymenium production, infection, and lesion development were 16-30, 20-26, and 20-30 C, respectively. Hymenium production was very minimal at temperatures above 30 C or at any temperature in the absence of misting (...)}, number={12}, journal={PLANT DISEASE}, author={SHEW, HD and MAIN, CE}, year={1990}, month={Dec}, pages={1009–1013} }
 @article{shew_beute_1979, title={EVIDENCE FOR THE INVOLVEMENT OF SOILBORNE MITES IN PYTHIUM POD ROT OF PEANUT}, volume={69}, ISSN={["0031-949X"]}, DOI={10.1094/Phyto-69-204}, abstractNote={SHEW, H. D., and M. K. BEUTE. 1979. Evidence for the involvement of soilborne mites in Pythium pod rot of peanut. Phytopathology 69:204-207. Mites of the genus Caloglyphus (Acarina: Acaridae) were associated with obtained from 90% of the fecal pellets collected from C. micheali after more than 50% of decaying peanut pods collected in a field in which pod rot feeding on mycelial mats of the fungus. P. myriotylum oospores also was caused by Pythium myriotylum. Laboratory cultures of these mites remained viable after passing through the alimentary canal of C. micheali. could be maintained for several months on Pythium aphanidermatum Pythium pod rot was reduced significantly in field and greenhouse tests of growing on potato-dextrose agar slant tubes. In food preference tests several acaricides and broad spectrum insecticides. In greenhouse tests the Caloglyphus micheali was attracted to P. myriotylum; up to 98% of all mites addition of soilborne mites to field soil infested with P. myriotylum responding in food preference tests preferred P. myriotylum over five other significantly increased the incidence of peanut pod rot. fungi isolated from peanut pods. Viable colonies of P. myriotylum were Additional key words: Pythium myriotylum, Caloglyphus spp. Although mites are the most numerous of all soilborne For mite identification, a single gravid female from each mite arthropods, only limited research has been conducted to investigate isolate was transferred to a new culture tube to ensure pure cultures the role of this group of organisms in the initiation of fungal (4,16) of mites for future work. Mites used for identification were and bacterial (6) plant diseases. Several reports of mites as pests of mounted in Hoyer's solution (15). Identification was made by M. peanut (Arachis hypogaea L.) are known. Caloglyphusrodionovi H. Farrier, Entomology Department, North Carolina State Zach. was capable of penetrating the peanut pod and feeding on the University, Raleigh, and by the authors. developing kernels (21). Mites of the genera Caloglyphus and Pod rot control and enhancement. A field test was conducted to Tyrophagus were isolated regularly from subterranean parts of evaluate the effectiveness of several acaricides and broad spectrum peanut plants in South Africa and under certain conditions insecticides in reducing pod rot incidence and severity. The field penetrated pods and increased percent colonization of these pods used had a history of Pythium pod rot. Seeds of peanut cultivar VA by Aspergillusflavus (Link) Fr. (1). 56 R were planted in early May and all standard agronomic Enhancement of peanut pod rot caused by Pythium myriotylum practices were observed throughout the growing season except for Drechs. has been reported in the presence of various soil flora (7,10) application of test insecticides and acaricides. These chemicals were and fauna (9,18) including soil mites (2,3). This study was applied at a rate of 2.24 kg Al/ha as a drench in a 30 cm band over undertaken to determine: (i) which mite species are associated with the row in mid July using approximately 655 L H20/ ha to apply the rotting pods in North Carolina; (ii) if mites enhance Pythium pod chemicals. Pod-rot data were collected the last of September. Plots rot development; and (iii) the possible mechanisms of miteconsisted of two 15.2 m rows and were replicated four times in a associated disease enhancement. randomized complete block design. The soil used in greenhouse tests was Norfolk fine sandy loam MATERIALS AND METHODS taken from the plow layer (top 18 cm) of the field described above. Cultivar NC 5 peanut plants were grown in containers 50 X 35 X 14 Isolates of P. myriotylum and all other fungi used in this study cm. Chemicals were applied as a drench at equivalent rates were isolated originally from peanut pods or plants. Stock cultures described for field tests. After 16 wk plants were rated for pod rot were maintained on glucose yeast-extract agar or potato-dextrose and mite populations were determined using the sugar flotationagar (PDA) at 24-26 C. Soilborne mites were obtained from peanut sieving method (3). pods decayed by P. myriotylum, pods that had overwintered in Pod rotha m t rea field soil, and from soil collected in a field with a history of Pythium plants grown in sterilized fine sandy loam soil in 50 X 35 p 14-cm pod rot. Mites were extracted from soil by a sugar flotation-sieving containersnin tereenhoue at 24-3 CTae in cl technique (3). containers in the greenhouse at 24-30 C. Treatments included Mitechnie (3)e ainfesting soil with (i) P. myriotylum plus mites, (ii) P. myriotylum Mite culture and identification. Following initial isolation of alone, (iii) mites alone, and (iv) no treatment (controls). Fungal mites from peanut pods and soil, mites were placed on agar slant inoculum was introduced by placing five oat grains, inoculated 10 tube cultures of Pythium aphanidermatum (Edson) Fitzp. days prior with P. myriotylum, into each corner of the containers growing on PDA at 24-30 C. New colonies were started by approximately 2.5 cm below the soil surface. Sterile oat grains were transferring 5-10 gravid females to a 5-day-old tube culture of P. substituted in treatments not receiving P. myriotylum. Mites were aphanidermatum. Only adult mites were used in in vitro introduced as atmixtu of isolte oto t ot gra experiments. introduced as a mixture of isolates onto the oat grains. Approximately five living mites were placed in each corner of the container. The soil was infested when the plants were 10 wk of age, 00031-949X/79/000035$03.00/0 the test ran for an additional 10 wk, and the test was repeated three 01979 The American Phytopathological Society times.}, number={3}, journal={PHYTOPATHOLOGY}, author={SHEW, HD and BEUTE, MK}, year={1979}, pages={204–207} }