Abstract
Seed shattering is important for wild plant species to guarantee efficient seed propagation. In rice, two shattering loci, sh4 and qSH1, with strong effects on seed shattering were previously identified through the map-based approach. In this study, a rice cultivar, Oryza sativa Japonica cv. Nipponbare, and an annual wild accession, O. rufipogon W630 were used as plant materials. The former contains non-functional alleles at sh4 and qSH1, whereas the latter has shattering alleles at both loci. Since the ancient humans selected non-shattering mutants in the past, it is important to evaluate shattering behavior of plants carrying non-functional alleles in the genetic background of wild rice. Therefore, O. sativa cv. Nipponbare was backcrossed twice with O. rufipogon, and backcross plants at BC2 generation were produced. Among them, the substitution plants having both cultivated alleles at sh4 and qSH1 loci in the genetic background of wild rice were selected by dCAPS and microsatellite markers. Using these lines and the parents, the temporal changes of shattering degree after flowering were examined based on the breaking tensile strength values for detachment of seeds from the pedicels. At 5 days after flowering, the shattering degrees of the substitution lines were almost similar to that of wild accession. They decreased moderately but maintained around half values of cultivated Nipponbare at 10 days after pollination. Probably, partial formation of abscission layers in pedicels might allow matured seeds to be kept on the panicles. These results suggest that the wild rice may still keep additional gene(s) promoting the formation of abscission layer besides qSH1 and sh4 alleles.
