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 varia tion for desirable alleles and the accurate characterization of the variabi lity within and among germplasm accessions in the collection, This study wa s conducted to survey the molecular variation in the converted race stock c ollection by using simple sequence repeat (SSR) DNA markers and to determin e the genetic distance of each race stock from a typical G. hirsutum cultig en, The molecular marker data will also provide a measure of the degree to which the recurrent photoperiodic parent has been recovered during backcros s conversion to day-neutral stocks. Fifty-six flourescently labeled SSR pri mer pairs arranged in multiplex bins were used to genotype 97 day-neutral B C4F4 race stock accessions, The majority of the accessions had genetic dist ances <0.25 from the G, hirsutum standard TMI. There was strong evidence th at the accessions were heterozygous or heterogeneous, so 10 plants were gen otyped within the most diverse nine accessions, those with genetic distance From TM1 >0.25. Zn some families, the primitive photoperiodic parent was r ecovered, and in others there was extensive linkage drag from the day-neutr al donor parent. The recovery of the primitive recurrent parent could be im proved by marker-assisted backcrossing with SSR markers reported in this ex periment. Careful genotyping with SSR markers prior to introgression into b reeding programs is suggested to ensure maximum genetic diversity and integ rity of the exotic race-stock donor germplasm.