Heterosis in numbers of differentiated, degenerated, and surviving spikelets and their relations to the dry matter production in F-1 hybrids of rice

Heterosis in the number of differentiated, degenerated, and surviving spike lets in two important Chinese F-1 hybrids Shanyou 63 (SY63) and Yayou 2 (YY 2) and their parents was observed under solution culture conditions, The re sults indicated that the number of differentiated, degenerated, and survivi ng spikelets all showed a very high value for mid-parental (MP) heterosis i n the hybrids at both panicle and plant levels. The increase in the number of surviving spikelets primarily depended on that of the number of differen tiated spikelets. The percentage of degenerated spikelets showed a positive value for MP and higher-parental (HP) heterosis (increase) in SY63, while it showed a negative value for NIP and HP heterosis (decrease) in YY2. Morp hologically, the components of the number of surviving spikelets increased in the hybrids, especially the number of surviving secondary rachis branche s. Dry matter production at heading showed a high value for MP and HP heter osis. However, the ratio of dry matter weight to the number of differentiat ed spikelets did not show a MP heterosis. The hybrids showed a lower percen tage of degenerated spikelets for the same ratio of dry matter weight to th e number of differentiated spikelets. The N uptake in the hybrids showed a MP and HP heterosis, but the efficiency of the N in producing the number of surviving spikelets showed a negative value for Mr and HP heterosis. The M r and HP heterosis in the sink-source ratio of the number of surviving spik elets to the leaf area varied considerably with the combinations. These fin dings suggested that still many characters could be further improved in F-1 hybrid rice.