Cultivated rice (Oryza sativa L.) was domesticated from Asian wild rice, O. rufipogon Griff. There are many morphological differences between them. Of these, wild rice has long awns at the tip of the seeds, whereas cultivated rice has no or short awns. In order to understand the genetic control of awn length, QTL analysis was carried out using BC2F8 backcross population between O. sativa cv. Nipponbare (a recurrent parent) and O. rufipogon acc. W630 (a donor parent). As a result, two strong QTLs were detected on chromosome 4 and 8. The allelic interaction at these loci was further examined using two sets of populations having reciprocal genetic backgrounds, cultivated and wild. In the genetic background of cultivated rice, the wild allele at the QTL on chromosome 8 had stronger effect on awn length than that on chromosome 4. On the other hand, in the genetic background of wild rice, the Nipponbare allele at the QTL on chromosome 4 produced shorter awns than that on chromosome 8. In addition, the wild backcross plants having Nipponbare homozygous alleles at both loci still showed half awns relative to the wild parent. This fact indicates that an awnless character was not simply obtained by these mutations. Probably, some other minor loci may be associated with awnless seed germination in cultivated rice.
