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Drought is a major constraint in some rice-growing areas of the United States. Its impact is most severe at the reproductive stage resulting in low grain yield. Therefore, assessment of genetic and phenotypic variation for drought tolerance in US rice germplasm is necessary to accelerate the breeding effort. Evaluation of 205 US rice genotypes for drought tolerance at the reproductive stage revealed tolerant response in rice genotypes Bengal, Jupiter, Cypress, Jazzman, Caffey, and Trenasse. Harvest index and fresh shoot weight were identified as important traits to explain the majority of variability among the genotypes under drought tolerance. Genotyping with 80 SSR markers indicated a low level of genetic diversity in US germplasm. Population structure analysis grouped the genotypes into eight clusters. The genotypes from California, Louisiana, and Arkansas formed distinct subgroups. Texas genotypes were similar to those from Louisiana and Arkansas. Marker-trait association analysis showed significant association of RM570 and RM351 with grain yield, spikelet fertility, and harvest index whereas shoot dry weight showed association with RM302 and RM461. The drought-tolerant genotypes identified in this study and the SSR markers associated with drought tolerance attributes will be helpful for development of improved drought-tolerant rice varieties through marker assisted selection.

During periods of drought, the irrigation needs of current warm-season turfgrass cultivars and frequent municipal water use restrictions present a major challenge to the turfgrass industry. Turfgrass breeding programs have responded by placing more emphasis on improved drought response. During 2012-2013, 560 genotypes of four warm-season turfgrass species developed by five southern breeding programs were evaluated for drought response in replicated field trials at seven locations. Breeders selected 35 genotypes as drought-tolerant selections (DTS) for further evaluation. The objectives of this study were to verify superior drought response among DTS under short-term drought conditions and to assess the effectiveness of this approach as a viable breeding strategy to improve drought response in warm-season turfgrasses. Forty-seven genotypes including standard commercial cultivars of zoysiagrass (Zoysia spp. Willd.), bermudagrass [Cynodon spp. (L.) Pers.], St. Augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze], and seashore paspalum (Paspalum vaginatum Swartz) were exposed to dry-downs in three consecutive years by withholding irrigation and excluding rainfall. Significant differences in drought performance were seen across genotypes over the multiyear study. Statistical contrasts found that DTS of zoysiagrass, St. Augustinegrass, and seashore paspalum generally Abbreviations: DGCI, dark green color index; DTS, drought-tolerant selection; NDVI, normalized difference vegetative index; %DGCI, percent of initial DGCI; %GC, percent of initial green cover; GC 50 , number of days of dry-down required to reduce green cover to 50% of the initial value; %NDVI, percent of initial NDVI; %TQ, percent of initial visual turf quality.