@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={AbstractThe 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 (H2) 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 H2 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 F1 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={AbstractSt. 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} }