Increasing yield potential in rice by exploitation of heterosis

摘要

The degree of heterosis in different hybrid rice varieties has the following general trend: indica/japonica > indica/javanica > japonica/javanica > indica/indica > japonica/japonica. The yield potential of the best existing indica/indica hybrids developed by the CMS system, in terms of per day per unit area, is around 75 kg/ha (from seed to seed), about 15% higher than pureline varieties. The best two-line system indica/indica hybrids can outyield CMS indica/indica hybrids by 5-10%.Heterosis of japonica/javanica hybrids could be used to increase japonica hybrid yields. Their grain quality retains japonica characteristics. Indica/japonica hybrids possess the highest yield potential in both sink and source. Theoretically, they may have a 30% yield advantage over the best existing indica/indica hybrids. However,there are some problems in such intersubspecific hybrids—semisterility, plants too tall, very long growth duration, and many poorly filled grains. So far, most problems have been overcome through two-line breeding methods, except for the poor filling of a number of fertilized grains. The strategy of developing very high-yielding indica/japonica hybrids for commercial production is discussed.