Posted on Dec 01, 2010
Critical problem. The single greatest hindrance to utilization of exotic germplasm in improvement of sorghum for temperate agriculture is that the vast majority of such germplasm flowers only at short daylength, as a result of the Ma1 gene conferring photoperiod sensitivity. Much effort in ‘conversion’ of exotic sorghums to day-neutral forms by a lengthy and tedious crossing program has rendered about 700 exotic sorghums more useful in breeding programs, however this remains only a tiny sampling of extant sorghum diversity.
Research approach. Over more than a decade of research, we ‘mapped’ the short-day flowering trait to a small region of the genome, sequenced the genome, scrutinized the ~30,000 genes in the sequence, and narrowed the list of candidates to about 400. In initial USCP funding to date, we have narrowed the target region to about 100 genes, and found tentative associations (albeit requiring further analysis) with one gene in particular. Herein, we seek to further test this association (and if need be seek and test other associations), by utilizing a ‘diversity panel’ of 384 genotypes that broadly samples worldwide sorghum diversity, provided by our cooperators H. Upadhyaya (germplasm curator), and C. T Hash (sorghum breeder) at ICRISAT. We expect the outcome to be the demonstration that different ‘versions’ (alleles) of one particular gene are closely correlated with differences in flowering time among members of the panel, indicating that the gene is Ma1. In addition, a fringe benefit will be to set the stage for the identification of the nearby dw2gene that accounts for much of the tall stature of exotic sorghums.
Potential benefits/impact. Identification of the specific gene responsible for short-day flowering would empower the use of a variety of mechanisms to ‘silence’ the gene, with the potential to cut many years from the conventional ‘conversion’ process. Over time, one could envision making most elite sorghums ‘impregnable’ to the Ma1 gene, such that most progeny of crosses between elite and exotic lines are immediately day-neutral in the F1. The nature of the gene and its native regulatory features may also suggest means by which one could exogenously induce short-day plants to flower (although this is less of a problem, in that simply covering with a trash can at night for 2-3 weeks is usually an adequate method).