Detection of dominant QTLs for stigma exsertion ratio in rice derived from Oryza rufipogon accession ‘W0120’

Stigma exsertion can enhance the outcrossing fertility in rice. Dominant genes for this trait are expected to be essential for the effective application of a novel outcrossing-based breeding system that uses male sterility in rice, which is normally autogamous. Because reduction of stigma exsertion is a domestication trait, we screened wild rice species as possible donors of genes or QTLs for stigma exsertion. We used in silico image-based screening and selected the Oryza rufipogon accession ‘W0120’. A single F1 individual derived from a cross between the japonica rice cultivar ‘Akidawara’ and ‘W0120’ was used to generate F2 and BC1F1 populations. QTL analysis performed using 114 F2 individuals detected QTLs on chromosomes 2, 3, 4, 8, and 11. Only two major QTLs on chromosomes 3 and 8 showed higher degrees of dominance. On the other hand, there were no QTLs near GS3, which is well known as a gene for stigma exsertion. Validation of these QTLs using 188 BC1F1 individuals provided clear evidence for their dominance. Genotypes of the markers nearest to the two QTLs were also related to grain length. We expect the genes responsible for these QTLs to be promising tools for improving outcrossing-based breeding in rice.