Genetics of Weediness in Sorghum halepense

Having spread to six continents from its Asian center of diversity, Sorghum halepense is considered a noxious weed for its competitiveness and invasiveness. It is a polyploid resulting from natural hybridization between S. bicolor (2n=20) and S. propinquum (2n=20), and is perennial in tropical and some temperate climates. Seed dispersal by shattering, and spread and overwintering by extensive rhizomes, make eradication of S. halepense difficult and expensive. To dissect the genetics of weediness, we have crossed a S. halepense accession from Kansas (USA) with the elite reference sorghum genotype BTx623, obtaining a tetraploid F1 hybrid. F2/F2:3 and BC1F2 populations derived from this F1 have displayed tremendous phenotypic variations. We are investigating a variety of traits that are related to “weediness” such as shattering and vegetative branching, and also quantifying flowering time, rhizomatousness, winter and spring growth at different developmental stages. An initial assay of 100 SSR markers has detected some QTLs for weediness in F2/F2:3, allowing comparisons to genes and QTLs identified in a diploid population derived from S. bicolor × S. propinquum (the progenitors of S. halepense).  Increased knowledge of the genetics of weediness might lead to new opportunities for discovering a genetic remedy for weed control. As a fringe benefit, adaptations of S. halepense to a wider range of environments than cultivated sorghum might make it a valuable source of novel alleles for sorghum improvement, such as early flowering, rapid vegetative growth, cold tolerance, and ratooning/perenniality.