Evaluation and analysis of commercial cultivars and elite breeding lines for resistance to the bacterial blight pathogen race 18 in cotton

Abstract

Cotton (Gossypium spp.) is an economically important crop which provides a significant source of fiber, animal feed, and food oil worldwide. Bacterial blight (BB), caused by Xanthomonas citri pv. malvacearum (Xcm), infects the aerial part of the cotton plant at all stages and can cause a significant loss in yield and fiber quality. In this study, 288 Upland (G. hirsutum) and 8 Pima (G. barbadense) commercial transgenic cultivars and elite breeding lines were divided into 10 replicated tests and evaluated for BB resistance using the toothpick scratching method in the greenhouse in 2016–2017. Five Upland and four Pima genotypes were used as resistant and susceptible controls, respectively. The percentage of susceptible plants with water-soaking symptoms was calculated on a replication basis for each genotype. While all the commercial Pima cultivars tested were susceptible, 21 commercial Upland cultivars were resistant to Xcm race 18. A total of 22 elite public breeding lines were resistant, including 11 lines from the University of Arkansas with an active breeding program for BB resistance and 1–4 resistant lines from five other public breeding programs without an active screening component for BB resistance. Of more than 150 breeding lines developed at New Mexico State University, 11 were found to be resistant to BB. Many commercial cultivars and public breeding lines were found to contain various levels of susceptible plants and are therefore heterogeneous in BB resistance. The results suggest that the resistance to Xcm race 18 can be easily bred in breeding without a selection pressure. A pedigree analysis showed that there are likely different sources of BB resistance. The resistant cultivars and lines identified should be a valuable resource to improve BB resistance in cotton breeding.