Development of hybrid rice is an important strategy to increase yields of irrigated rice in China. Day length is a highly important environmental factor for hybrid rice adaptability,productivity and quality. Heterosis of hybrid rice has been utilized under natural-(long) day length conditions in the middle and lower reaches plain of Yangtze River Valley in China for a long time. However,whether the hybrid rice can show heterosis under short-day length conditions is unknown. In this study,we analyzed plant height,grain number per panicle,and other yield related traits of hybrid rice Liangyoupeijiu(LYP9) and its parents(Pei'ai 64 S and 93-11) under natural- and short-day length conditions and compared the respective heterosis. Results showed that earlier heading,reduced plant height,and reduced grain number per panicle were found in these three varieties under short-day length conditions relative to those under natural-day length conditions. In either natural- or short-day length conditions,heterosis of LYP9 was mainly displayed in grain number per panicle and plant height. This study may help in breeding and selecting suitable hybrid rice for different regions with natural- or short-day length.
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