Molecular Genetic Mapping of the Major Effect Photoperiod Response Locus in Pima Cotton (Gossypium barbadense L.).

Photoperiod sensitivity is a major barrier for the introgression from the tropical gene pool to be used in the cotton breeding programs in North America. To better understand the genetic processes underlying photoperiod response in Pima cotton, a photoperiod insensitive line Pima S-7 was crossed to a photoperiod sensitive landrace accession NC7018. An F₂ mapping population of 211 individuals was used to establish that a single dominant gene controls the photoperiod sensitivity in Gossypium barbadense. Molecular mapping with simple sequence repeat (SSR) markers localized the photoperiod response gene Gb_Ppd1 into a 3.3 cM region on chromosome 25 of the Pima cotton genetic map. Orthologous mapping of the flanking markers with the draft diploid D-genome sequence resolved the photoperiod response gene to a 5.8 Mb region close to centromere on chromosome 10 of Gossypium raimondii. In silico mapping of the flowering time candidate genes of model plant species suggested that putative gene Gorai.010G161200 of G. raimondii, which has a function involved in photoperiodism, was mapped in the genomic region of Gb_Ppd1. Identification of closely linked molecular markers and the delineated genomic region in sequenced G. raimondii genome will aid marker assisted selection and molecular isolation of photoperiod response loci in cotton.