@article{simpson_haverroth_taggart_andrade_villegas_carbajal_oliveira_suchoff_milla-lewis_cardoso_2024, title={Dehydration tolerance rather than avoidance explains drought resistance in zoysiagrass}, volume={176}, ISSN={["1399-3054"]}, url={http://dx.doi.org/10.1111/ppl.14622}, DOI={10.1111/ppl.14622}, abstractNote={Abstract Irrigation of grasses dominates domestic water use across the globe, and better understanding of water use and drought resistance in grasses is of undeniable importance for water conservation. Breeding programs have released cultivars with improved drought resistance, but the underlying mechanisms remain unknown. We sought to characterize the mechanisms driving drought resistance in four zoysiagrass cultivars (Lobo, Zeon, Empire, and Meyer) reported to exhibit contrasting levels of drought resistance. A dry‐down was performed through deficit irrigation until 70% decline in evapotranspiration. All cultivars exhibited similar drought avoidance as they dehydrated similarly throughout the drought. Lobo and Zeon, however, exhibited a 70% decline in evapotranspiration two to three days after Empire and Meyer, thus experiencing lower water potentials. Regarding drought tolerance, Lobo and Zeon maintained higher normalized difference vegetation index (NDVI) and lower perceived canopy mortality at higher dehydration levels than Empire and Meyer. We use “perceived” because visual assessments of canopy mortality are influenced by drought‐induced leaf rolling. During the recovery, leaves rehydrated and unrolled, so the “actual” canopy mortality could be evaluated. All cultivars exhibited similar mortality on the first recovery day despite Lobo and Zeon experiencing more severe dehydration. Throughout the recovery, Lobo and Empire exhibited faster re‐growth and showed the lowest canopy mortality, and Lobo exhibited the highest NDVI. The improved drought resistance of Lobo and Zeon results from greater dehydration tolerance rather than avoidance. This study has implications for lawn owners selecting the best cultivars and for breeding programs aiming at improving drought resistance of zoysiagrasses.}, number={6}, journal={PHYSIOLOGIA PLANTARUM}, author={Simpson, Emma and Haverroth, Eduardo J. and Taggart, Matthew and Andrade, Moab T. and Villegas, Daniel A. and Carbajal, Esdras M. and Oliveira, Leonardo A. and Suchoff, David and Milla-Lewis, Susana and Cardoso, Amanda A.}, year={2024}, month={Nov} }
 @article{milla-lewis_gouveia_kenworthy_zhang_chandra_miller_carbajal_schwartz_raymer_pudzianowska_et al._2024, title={Maximizing genetic gains across agronomic and consumer preference traits in St. Augustinegrass breeding}, volume={10}, ISSN={["1435-0653"]}, url={https://doi.org/10.1002/csc2.21374}, DOI={10.1002/csc2.21374}, abstractNote={Abstract Combining large multi‐environment trial (MET) datasets to decide which genotypes to move forward in the breeding process can be challenging, especially when dealing with negatively correlated traits. The use of a selection index has long been identified as an effective strategy in these situations. However, the method has found limited application in turfgrass breeding. The objective of this study was to use MET data for St. Augustinegrass [ Stenotaphrum secundatum (Walt.) Kuntze] breeding lines evaluated across the southern United States to compare genetic gains achieved with the additive additive genetic index (AI) versus the turf performance index (TPI) incorporating agronomic as well as consumer preference traits. The use of either selection index produced more positive genetic gains across traits than direct selection even in the presence of negative correlations. However, the higher genetic gains obtained with AI versus TPI indicate that the use of an index that weighs traits according to their importance is a better approach for selection. Moreover, under a more stringent selection intensity, none of the best lines identified with AI would have been selected with TPI emphasizing the importance of choosing selection criteria that provide a more nuanced ranking of lines. Additionally, higher heritability values and gains from selection were obtained for turfgrass quality under stress (drought and shade) than under normal conditions indicating that selection under stress environments might be more efficient. Most of the evaluated St. Augustinegrass lines outperformed the checks, further supporting the value of cross‐institutional breeding collaborations.}, journal={CROP SCIENCE}, author={Milla-Lewis, Susana R. and Gouveia, Beatriz Tome and Kenworthy, Kevin and Zhang, Jing and Chandra, Ambika and Miller, Grady L. and Carbajal, Esdras M. and Schwartz, Brian and Raymer, Paul and Pudzianowska, Marta and et al.}, year={2024}, month={Oct} }
 @article{laat_leon_dale_gouveia_carbajal_schiavon_unruh_iannone iii_milla-lewis_2024, title={Molecular analysis of St. Augustinegrass cultivar mixtures composition over time and latitude}, volume={9}, ISSN={["1435-0653"]}, url={https://doi.org/10.1002/csc2.21370}, DOI={10.1002/csc2.21370}, abstractNote={Abstract St. Augustinegrass [ Stenotaphrum secundatum (Walt.) Kuntze] is commonly planted in residential and commercial landscapes as a cultivar monoculture predisposing this lawn to pest invasion and high‐maintenance inputs. Researchers have suggested that increasing genetic diversity by growing cultivars in mixtures may increase turfgrass stress resilience. However, the stability and uniformity of those mixtures has not been studied. The present study was carried out to evaluate the stability of St. Augustinegrass cultivars mixtures over time and across three latitudes. The study was conducted in Citra and Fort Lauderdale, FL, and Jackson Springs, NC. Simple‐sequence repeats markers were used to genotype leaf samples of St. Augustinegrass cultivars planted in two‐ and four‐cultivar mixtures. Leaf samples were collected 1 and 3 years after establishment. In all locations, cultivar richness and evenness declined over time. Similarly, the relative abundance of the least persistent cultivars decreased approximately 50%–100% depending on cultivar and location. Differences in growth patterns among cultivars resulted in cultivar displacement and the predominance of a single cultivar. Cultivars that covered the ground faster or formed dense canopies early after establishment were dominant at the end of the study. Locally developed cultivars tended to be more dominant in their original latitude. The use of cultivar mixtures may help the identification of vigorous, competitive, and stress tolerant cultivars in turfgrass breeding programs. However, their commercial use remains challenging as if the patterns observed here for 3 years are representative of a continuous trend, and they do not persist over time.}, journal={CROP SCIENCE}, author={Laat, Rocio and Leon, Ramon G. and Dale, Adam G. and Gouveia, Beatriz and Carbajal, Esdras M. and Schiavon, Marco and Unruh, J. Bryan and Iannone III, Basil and Milla-Lewis, Susana R.}, year={2024}, month={Sep} }
 @article{rockstad_austin_gouveia_carbajal_milla-lewis_2023, title={Assessing unmanned aerial vehicle-based imagery for breeding applications in St. Augustinegrass under drought and non-drought conditions}, volume={12}, ISSN={["1435-0653"]}, url={https://doi.org/10.1002/csc2.21128}, DOI={10.1002/csc2.21128}, abstractNote={Abstract The use of imagery collected from small unmanned aerial vehicles (UAVs) in turfgrass breeding has rapidly increased, as has the demand to develop drought‐resistant cultivars. However, prior to adopting UAVs to help guide turfgrass selection under drought stress conditions, a clear understanding of the value and predictive ability of imagery‐based turfgrass characterization is required. In St. Augustinegrass, a major warm‐season turfgrass species grown in the Southeastern United States, limited research has been published about characterizing drought stress using aerial imagery. Specifically, no efforts have compared the various vegetation indices (VIs) commonly used to evaluate vegetative health in other species and sought to identify the most useful index for phenotyping drought stress traits in St. Augustinegrass. In this study, traditional ground‐based approaches for measuring percent green cover (PGC) and normalized difference vegetation index (NDVI) were compared against their UAV‐derived counterparts as well as 13 VIs under drought and non‐drought conditions, and broad‐sense heritability (H 2 ) was calculated. A population of 115 genotypes from a ‘‘Raleigh’’ × ‘‘Seville’’ cross were analyzed at two environmentally distinct field sites in North Carolina. At both sites, a significant relationship between ground‐based and UAV‐derived measurements for PGC and NDVI was observed before and during drought ( r = 0.82 to 0.95) and suggests a clear advantage to using UAVs for phenotyping drought traits given the reduced time and labor costs compared to on‐ground efforts. Among all VIs compared, UAV‐derived NDVI (NDVI‐U) showed strong correlation with the PGC taken on the ground ( r > 0.85), a similar trend over time, and a higher H 2 estimate under drought conditions, suggesting that NDVI‐U has the potential to assist in the selection of St. Augustinegrass genotypes with the best phenotypic response to drought. Implementing UAV imagery‐based high‐throughput methods will allow breeders to evaluate germplasm with unbiased quantitative consistency, quickly and thoroughly, and with increased frequency—all without sacrificing the response to selection potential.}, journal={CROP SCIENCE}, author={Rockstad, Greta B. G. and Austin, Robert E. and Gouveia, Beatriz T. and Carbajal, Esdras M. and Milla-Lewis, Susana R.}, year={2023}, month={Dec} }
 @article{yu_lara_carbajal_milla-lewis_2022, title={QTL mapping of morphological characteristics that correlated to drought tolerance in St. Augustinegrass}, volume={17}, ISSN={["1932-6203"]}, DOI={10.1371/journal.pone.0268004}, abstractNote={St. Augustinegrass is a warm-season grass species widely utilized as turf in the southeastern U.S. It shows significant variation in plant growth and morphological characteristics, some of which are potentially associated with drought tolerance. However, the genetic basis of these variations is not well understood. Detecting quantitative trait loci (QTL) associated with morphological traits will provide a foundation for the application of genetic and molecular breeding in St. Augustinegrass. In this study, we report QTL associated with morphological traits, including leaf blade width (LW), leaf blade length (LL), canopy density (CD), and shoot growth orientation (SGO) in a St. Augustinegrass ‘Raleigh’ x ‘Seville’ mapping population containing 115 F 1 hybrids. Phenotypic data were collected from one greenhouse and two field trials. Single and joint trial analyses were performed, finding significant phenotypic variance among the hybrids for all traits. Interval mapping (IM) and multiple QTL method (MQM) analysis detected seven QTL for CD, four for LL, five for LW, and two for SGO, which were distributed on linkage groups RLG1, RLG9, SLG3, SLG7, SLG8 and SLG9. In addition, three genomic regions where QTL colocalized were identified on Raleigh LG1 and Seville LG3. One genomic region on Seville LG3 overlapped with two previously reported drought-related QTL for leaf relative water content (RWC) and percent green cover (GC). Several candidate genes related to plant development and drought stress response were identified within QTL intervals. The QTL identified in this study represent a first step in identifying genes controlling morphological traits that might accelerate progress in selection of St. Augustinegrass lines with lower water usage.}, number={5}, journal={PLOS ONE}, author={Yu, Xingwang and Lara, Nicolas A. H. and Carbajal, Esdras M. and Milla-Lewis, Susana R.}, year={2022} }
 @article{graham_gouveia_carbajal_laat_milla-lewis_2022, title={Using base index for selection of St. Augustinegrass breeding lines evaluated in multienvironment trials for turfgrass quality traits and stress tolerance in North Carolina}, volume={7}, ISSN={["1435-0653"]}, url={https://doi.org/10.1002/csc2.20755}, DOI={10.1002/csc2.20755}, abstractNote={Abstract St. Augustinegrass [ Stenotaphrum secundatum (Walt.) Kuntze] is a warm‐season turfgrass primarily used for home lawns and commercial landscapes in the southern United States. New cultivars that possess desirable turfgrass quality (TQ) in combination with improved tolerance to diseases, drought and cold are needed to increase the sustainability of St. Augustinegrass production and maintenance in transitional zones. This study's objectives were to evaluate breeding lines in multienvironment trials across North Carolina to (a) assess relationships among economically important traits, and (b) select genotypes with stable performance across environments. Sixty‐one St. Augustinegrass genotypes and five commercial checks were established in replicated field trials at three locations across North Carolina. Entries were evaluated for rate of establishment, TQ, turfgrass stand density, genetic color, leaf texture, uniformity, winter survival, fall color, drought tolerance, and gray leaf spot resistance from 2017 to 2020. Best linear unbiased predictions were used to calculate a selection index to identify elite genotypes across traits. The 10 traits were clustered into three groups: winter survival and fall color; genetic color, leaf texture, and gray leaf spot resistance; and establishment rate, TQ, density, uniformity, and drought tolerance. Selection of the top 10 genotypes using the selection index resulted in positive estimated genetic gains for all 10 traits, indicating it is an effective method for simultaneous selection. Line XSA 14271 outperformed ‘Palmetto’, ‘Raleigh’, ‘Captiva’, and ‘Seville’, for several traits and was the top‐ranked line. It will be advanced to on‐farm trials to evaluate sod production traits to assess its potential for commercial release.}, journal={CROP SCIENCE}, author={Graham, Sydney E. and Gouveia, Beatriz Tome and Carbajal, Esdras M. and Laat, Rocio and Milla-Lewis, Susana R.}, year={2022}, month={Jul} }
 @article{yu_brown_graham_carbajal_zuleta_milla-lewis_2019, title={Detection of quantitative trait loci associated with drought tolerance in St. Augustinegrass}, volume={14}, ISSN={["1932-6203"]}, DOI={10.1371/journal.pone.0224620}, abstractNote={St. Augustinegrass (Stenotaphrum secundatum) is a warm-season grass species commonly utilized as turf in the southeastern US. Improvement in the drought tolerance of St. Augustinegrass has significant value within the turfgrass industry. Detecting quantitative trait loci (QTL) associated with drought tolerance will allow for advanced breeding strategies to identify St. Augustinegrass germplasm with improved performance for this trait. A multi-year and multi-environment study was performed to identify QTL in a 'Raleigh' x 'Seville' mapping population segregating for phenotypic traits associated with drought tolerance. Phenotypic data was collected from a field trial and a two-year greenhouse study, which included relative water content (RWC), chlorophyll content (CHC), leaf firing (LF), leaf wilting (LW), green cover (GC) and normalized difference vegetative index (NDVI). Significant phenotypic variance was observed and a total of 70 QTL were detected for all traits. A genomic region on linkage group R6 simultaneously harbored QTL for RWC, LF and LW in different experiments. In addition, overlapping QTL for GC, LF, LW and NDVI were found on linkage groups R1, R5, R7 and S2. Sequence alignment analysis revealed several drought response genes within these regions. The QTL identified in this study have potential to be used in the future to identify genes associated with drought tolerance and for use in marker-assisted breeding.}, number={10}, journal={PLOS ONE}, author={Yu, Xingwang and Brown, Jessica M. and Graham, Sydney E. and Carbajal, Esdras M. and Zuleta, Maria C. and Milla-Lewis, Susana R.}, year={2019}, month={Oct} }