Sorghum Ma5 and Ma6 maturity genes

The Ma5 and Ma6 maturity loci in sorghum contain genes interacting epistatically to block flowering until an appropriate daylength is met. Because sorghum is a crop of tropical origin, its critical daylength is close to 12 hours. Sorghums with dominant alleles at these two loci are photoperiod sensitive, extremely late flowering, and ill-suited to cultivation in the temperate U.S. Most sorghum lines grown in the U.S. have been converted to photoperiod insensitive plants that have recessive mutations at the ma6 locus. This work describes ongoing efforts to clone the genes responsible for the Ma5/Ma6 ? controlled late flowering response in sorghum. To reach this goal, the two loci were mapped with AFLP and SSR markers that were part of an integrated genetic, physical, and cytogenetic map of the sorghum genome. Genetic markers have been linked to both the Ma5 and Ma6 loci on chromosomes 2 and 6, respectively. BAC libraries have been screened to identify numerous BACs associated with each locus. Additional work to fine-map each locus and identify potential candidate genes by comparison with the rice genome is ongoing.