Utilization of Natural Diversity in Upland Cotton ( G . hirsutum ) Germplasm Collection for Pyramiding Genes via Marker-assisted Selection Program

Cotton is the world’s leading cash crop, but it lags behind other major crops for marker-assisted breeding that underlies a need for characterization, tagging, and utilization of existing natural polymorphisms in cotton germplasm collections. Previously, we conducted molecular genetic analyses in a global set of ~1000 G. hirsutum accessions from Uzbek cotton germplasm collection, representing, at least, 37 cotton growing countries and 8 breeding ecotypes as well as wild landrace stock accessions. The important fiber quality (fiber length and strength, micronaire, uniformity, reflectance, elongation and ect.) traits were measured in two distinct environments of Uzbekistan and Mexico. This study allowed us to design an “association mapping” (mixed liner model-MLM) study to find biologically meaningful markertrait associations for important fiber quality traits in Upland cotton that accounts for population confounding effects. Several SSR markers associated with main fiber quality traits along with donor accessions were selected to be used for marker-assisted selection (MAS) programs. In this study, utilizing our previous results of association mapping in Uzbek cotton germplasm resources, with specific objective of introducing and enriching the currently-applied traditional breeding approaches with more efficient modern MAS tools in Uzbekistan, we began marker-assisted selection efforts using molecular markers associated with important fiber traits. For this purpose, we selected 1) major fiber quality trait – associated SSR markers and 2) donor genotypes that were identified in our previous studies. We selected 23 major (micronaire, fiber strength and length, and elongation) fiber trait-associated DNA markers as a tool to control the transferring of QTL loci during a genetic hybridization. We selected 37 (11 wild race stocks and 26 variety accessions from diverse ecotypes) donor cotton genotypes that bear important QTLs for fiber traits. These donor genotypes were crossed with 9 commercial cultivars of Uzbekistan (as recipients) in various combination with objective of improving one or more of fiber characteristics of these recipients. These 9 parental recipient genomes preliminarily were screened with our DNA-marker panel to compare with 37 donor genotypes. The polymorphic states of marker bands between donor and recipient genotypes were recorded. The subsequent generation of hybrid plants from each crossing combination were tested using DNA-markers at the seedling stage and hybrids bearing DNA-marker bands from donor plants were selected for further backcross breeding. Testing the major fiber quality traits using HVI in traitassociated marker-band-bearing hybrids revealed that mobilization of the specific marker bands from donors really have positively improved the trait of interest in recipient genotypes. Currently, we developed a second generation of recurrent parent backcrossed hybrids (F1BC2), bearing novel marker bands and having superior fiber quality compared to original recipient parent (lacking trait-associated SSR bands). These results showed the functionality of the trait-associated SSR markers detected in our association mapping efforts in diverse set of Upland cotton germplasm. Using these effective molecular markers as a breeding tool, we aim to pyramid major fiber quality traits into single genotype of several commercial Upland cotton cultivars of Uzbekistan.