Simple sequence repeat-based assessment of genetic diversity in cotton race stock accessions

Effective use of converted day-neutral Gossypium hirsutum L. race stocks in cotton genetic improvement programs depends on the extent of genetic variation for desirable alleles and the accurate characterization of the variability within and among germplasm accessions in the collection, This study was conducted to survey the molecular variation in the converted race stock collection by using simple sequence repeat (SSR) DNA markers and to determine the genetic distance of each race stock from a typical G. hirsutum cultigen, The molecular marker data will also provide a measure of the degree to which the recurrent photoperiodic parent has been recovered during backcross conversion to day-neutral stocks. Fifty-six flourescently labeled SSR primer pairs arranged in multiplex bins were used to genotype 97 day-neutral BC4F4 race stock accessions, The majority of the accessions had genetic distances <0.25 from the G, hirsutum standard TMI. There was strong evidence that the accessions were heterozygous or heterogeneous, so 10 plants were genotyped within the most diverse nine accessions, those with genetic distance From TM1 >0.25. Zn some families, the primitive photoperiodic parent was recovered, and in others there was extensive linkage drag from the day-neutral donor parent. The recovery of the primitive recurrent parent could be improved by marker-assisted backcrossing with SSR markers reported in this experiment. Careful genotyping with SSR markers prior to introgression into breeding programs is suggested to ensure maximum genetic diversity and integrity of the exotic race-stock donor germplasm.