Molecular Biological Studies On Character Correlated With Heterosis In Rice (Oryza Sativa L.)

1 Introduction With the development of social economy, greater demand was put on world food production due to the decreasing arable lands and increasing global population. The yield increase of rice, a main staple for a large fragment of the word population, would contribute significantly to cope with the global food crisis. Heterosis application was the principal way to improve rice grain yield. In recent years, hybrid rice were grown on 15.55-16.00 million ha in China, 50% of the total rice area and 57% of China's total rice production. Hybrid rice normally had a yield average of 6.6OtIha, a 20-30% increase compared to conventional cultivars (Yuan Longping 1996, 1999). It had been regarded as a crucial technique for boosting rice production by UNFAO and some developing countries. Up till now, scientists and breeders abroad do not think they can find an alternative way. Hybrid rice have been introduced and popularized in 20 countries and regions. However, the yield level of hybrid rice had been stagnated for almost 20 years. Breeders have been making great effort to change the statue on many aspects, with no significant progress. The popularly used varieties in commercial production are restricted to a few elite combinations. There may be many explanations. The obscure understanding of the mechanism of heterosis may be the most explanatory. Fertility-restoring gene, heterosis and male sterility were the three important characters of heterosis application in rice. Many useful results were obtained from studies conducted in domestic and abroad. However there are points to be perfected: Many hypotheses were proposed on the heredity of restoring gene(s), molecular map location is far from perfect and molecular markers obtained could not be used to assist the breeding practice; Many methods were presented to predict the heterosis, but no expected results were acquired; Studies of the relationship between cytoplasm and male sterility were focused on mitochrondria, few were on chloroplast. DNA molecular techniques, developed in the late 1980's, were informative, covering most of genome, free of the effect of environment and crop development, and can be applied to characterize directly the crop genetic materials. The emergence and rapid development of molecular marker techniques has greatly enhanced the construction of genetic map in eukaryotic and chromosome location, positional cloning, and marker-assisted selection of target genes. Meanwhile, it provided molecular techniques for scientists to eluciate the mechanism of heterosis and to predict heterosis. In this paper, genetic feature of wide-abortive restoring genes, prediction of heterosis and the relationship between male sterility and chloroplast were investigated with molecular markers. The main results were as followed: 2. Molecular marker assay of wild-abortive restoring genes 2.1 Heredity of WA restoring genes in indica rice analyzed by using maxium likelihhood method The traits conferred by restoring genes, seed-setting rate or pollen fertility, is greatly affected by physiological, climatic and soil factors. The fertility of hybrid F2 population displays a non-normal continuous distribution, characteristic of qualitative-quantitative traits, so it was not practical to formulize fertility according to the same criterion and index. Various results were obtained due to various index and fertility-classifying criteria employed by different researchers. Maximum likelihood...