Quantitative Trait Loci for Seed Shattering and Seed Dormancy in Weedy Red Rice.

Red rice, a major weed in rice growing areas of the southern United States, is used as a model to elucidate the genetic basis of weediness with special emphasis on seed dormancy and seed shattering, which are two key traits for survival and persistence of the majority of weed species.  Both traits were evaluated in two recombinant inbred line (RIL) populations developed from the crosses, Bengal x PSRR-1 and Cypress x PSRR-1.  Bengal and Cypress are two non dormant and shattering resistant rice cultivars whereas PSRR-1 is a red rice accession with high intensity of shattering and seed dormancy. In Bengal x PSRR-1 population, QTL mapping indicated three major QTLs for seed shattering on chromosomes 2, 3, and 4 that explained 13.2, 9.3, and 10.9 % of the phenotypic variation, where as three QTLs on chromosome 7 and one on chromosome 1 were identified for seed dormancy with 5.8 to 18.9% of phenotypic variation.  There are two major QTLs each explaining 15-26% of the phenotypic variation for both seed shattering and seed dormancy located on chromosomes 4, 8 and 3, 7 respectively in Cypress x PSRR-1 population. Only one QTL for each trait was consistently expressed in both populations indicating the influence of genetic background on trait expression.  PSRR-1 alleles enhanced seed shattering and seed dormancy in most cases with the exception of the QTL for seed shattering on chromosome 8 in Cypress x PSRR-1 population. Near-isogenic lines are being developed to clone the major QTLs for these traits. The result from this model monocot will prove valuable to breed cultivars with preharvest sprouting tolerance and to understand the plant domestication process.