Utilization of weedy rice for development of japonica hybrid rice (Oryza sativa L.).

Two representative weedy rice lines, three typical japonica varieties and three typical indica varieties were used for 6 pairs of reciprocal crosses. The morphological traits of twelve F(1) hybrid lines, their parents and four elite cultivars were investigated for heterosis over mid-parent (HM), over parent (HP) and competitive heterosis (CH) analysis. Traits detected in weedy rice lines seemed larger than those in cultivars and excellent heterosis was produced in weedy rice crossing with japonica rice. Although weedy rice kept closer relationships with japonica rice compared to indica rice. But the heterosis of reciprocal crosses between weedy rice and japonica was closed to those of crosses between indica rice and japonica rice. In six of one hundred and eighteen weedy rice lines, the fertility restore gene for BT type cytoplasmic male sterility (BT-CMS) were detected. Weedy rice was very valuable germplasm resources with the abundant polymorphism. Meanwhile, the disadvantage, lodging, shattering and incompact plant type, should be modified by hybridization, backcross and multiple cross with japonica rice. Although it is difficult to use weedy rice directly, weedy rice may be available to breed both male sterile line and restorer line through improvement, developing japonica hybrid rice.