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Abstract
Heterosis in the number of differentiated, degenerated, and surviving spikelets in two important Chinese F1 hybrids Shanyou 63 (SY63) and Yayou 2 (YY2) and their parents was observed under solution culture conditions. The results indicated that the number of differentiated, degenerated, and surviving spikelets all showed a very high value for mid-parental (MP) heterosis in the hybrids at both panicle and plant levels. The increase in the number of surviving spikelets primarily depended on that of the number of differentiated 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 MP and HP heterosis (decrease) in YY2. Morphologically, the components of the number of surviving spikelets increased in the hybrids, especially the number of surviving secondary rachis branches. Dry matter production at heading showed a high value for MP and HP heterosis. However, the ratio of dry matter weight to the number of differentiated spikelets did not show a MP heterosis. The hybrids showed a lower percentage of degenerated spikelets for the same ratio of dry matter weight to the 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 MP and HP heterosis. The MP and HP heterosis in the sink-source ratio of the number of surviving spikelets to the leaf area varied considerably with the combinations. These findings suggested that still many characters could be further improved in F1 hybrid rice.
