Integration of multi-omics approaches reveals candidate genes for drought stress in St. Augustinegrass (Stenotaphrum secundatum)

There is growing demand across the turfgrass industry for turfgrasses that require minimal watering. St. Augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze], a warm-season turfgrass favored in the southeastern United States for its shade tolerance and vigorous stoloniferous growth, falls short in drought resistance. Integrating genomic and conventional breeding methodologies could accelerate the introduction of cultivars that thrive with less water. In this study, a population derived from the cross of breeding lines XSA10098 and XSA10127 was evaluated for drought resistance in field trials, where percent green cover and normalized difference vegetation index were collected by unmanned aerial vehicle-based phenotyping. A multiple quantitative trait loci (QTL) mapping approach identified 22 QTL, with overlapping regions on linkage groups 1, 2, 4, and 9 between this and previous studies. In addition, a detailed transcriptomic analysis on the roots of two St. Augustinegrass genotypes with contrasting drought responses revealed 1642 and 2669 differentially expressed genes (DEGs) in the drought-tolerant and drought-sensitive genotypes, respectively. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes classification showed different pathways adopted by the two genotypes in response to drought stress. Moreover, integration of QTL mapping and transcriptomic analyses identified five DEGs co-localized in overlapping QTL regions, which exhibit great value to potentially serve as targets to facilitate marker-assisted selection. The findings in this study contribute to a deeper understanding of the genetic basis of drought tolerance in St. Augustinegrass, facilitating the development of more robust breeding strategies for enhancing drought resilience in this important turfgrass species.