Genetic diversity of day-neutral converted landrace Gossypium hirsutum L. accessions

Upland cotton, Gossypium hirsutum L., is an important fiber crop that is grown in warmer climates in over seventy-five countries through-out the world and accounts for over 90% of world production. In this study we assessed the genetic diversity and population structure of 1115day-neutral conversions of G. hirsutum L. landrace accessions (DNCA). One-hundred-thirty-four genome wide simple sequence repeat markers were used for genotyping and 192 polymorphic loci were identified. A total of 1560 alleles were identified across the DNCAs and a set of 14 US cultivars with 64% being unique to DNCAs and only 6% were unique to the cultivars. Alleles ranged from 36 on chromosome 13 to 93 on chromosome 076. The relationship matrix indicated that, as a group, the DNCAs were not closely related, and the analysis resulted in seven distinct groupings, but these were not related to the country of origin. Analysis of molecular variance revealed that most of the variation (58.3%) was due to diversity within geographic origin groups and 41.7% due to diversity among groups. Within western hemisphere or eastern hemisphere origin of collection, there is a high degree of common allele sharing, but across hemispheres, DNCAs share fewer common alleles. Accessions originating in the eastern hemisphere share 56.8-65% of alleles in common with US cultivars; whereas, accessions originating in western hemisphere share between 38 and 41% of alleles in common with US cultivars. This study identified extensive genetic diversity among DNCAs within G. hirsutum.