QTL analysis for awnlessness using a backcross population between Oryza rufipogon and O. sativa IR36

Abstract

Long seed awning in wild rice is one of the propagation-related traits in natural habitats. During rice domestication, plants with shorter awns may gradually be selected because long awns disturb seed harvesting and handling. To clarify the domestication process of awnless rice, we first produced 146 backcross recombinant inbred lines at BC₂F₇ generation between Oryza rufipogon W630 (a recurrent parent) and O. sativa IR36 (a donor parent). Of these, a single line of G5 having shortest awns was selected. The G5 backcross recombinant inbred line was found to have IR36 homozygous alleles at 20 out of 167 SSR marker loci, showing seven IR36 chromosomal segments in the wild genetic background. The G5 line was further crossed with W630, and 160 BC₃F₂ progenies were generated. They were planted in the paddy field, and QTL analysis for awnlessness was carried out using awn length data at 5th spikelet position. As a result, one minor QTL and two major QTLs were detected on chromosomes 2 and 4, respectively. According to the associated marker positions, two major QTLs on chromosome 4 seem to be identical to An-1 and LABA1 loci, and the QTL on chromosome 2 may be a novel locus. Although these QTLs explained most of the awn length difference between O. rufipogon W630 and the G5 line, some other minor loci for awnlessness may still exist in the genome of awnless IR36.