Study On The Environmental Variation And Genetic Mechanism Of Heterosis On Yield Traits Of Japonica Rice In Cold Region

The utilization of heterosis is one of important approach to improve rice yields. The increase of rice yields per unit by utilization of heterosis is an important measure to stabilize and develop the yield of Japonica in northern china. Heilongjiang Province is an important production base of commodity food, responsible for the national food security. Therefore, the increase of rice yields by utilization of rice heterosis is of important scientific value and strategic significance on the theory and practice of ultra-high-yield rice breeding and the national food security.Heilongjiang Province Located the northern cold region for rice planting, which has short growth period, low temperature and less effective accumulated temperature. Therefore, the question about rice heterosis and its future in application are highly controversial. In this study, we selected 7 rice varieties of different types for cold region to generate 21 cross combinations with the Griffing Modelâ…£. The genetic mechanism and environmental variation on rice heterosis of yield traits were investigated to provide the theoretical basis for the utilization and prospect of heterosis in Sanya, Hainan Province and Harbin, Heilongjiang Province respectively. The main results were as follows: Significant genetic differences in five yield traits were observed between 7 parents and 21 combinations under different ecological conditions. The effect of different ecological environments on the yield per plant, panicles per plant, and average panicle length per plant and grain weight was significant. There was significant interaction effect between panicles per plant, average panicle length per plant, grain weight in F1 generation and the environment. The yield traits of F1 generation were controlled by genes and affected by environmental. The effect of environment on different yield traits was different.The heterosis of yield traits in F1 generation was different under different ecological conditions. The numbers of grain per plant, average panicle length per plant in more than 75% combinations showed a positive mid-parent heterosis under two environmental conditions. The grain yield per plant, panicles per plant and grain weight in 75% combinations showed a positive mid-parent heterosis in Sanya. The average panicle length per plant in 21 combinations showed a positive heterosis. The average panicle length per plant in more than 50% combinations showed a positive ultra-parent heterosis under two ecological conditions. The grain yield per plant and grain weight showed a positive ultra-parent heterosis only in Sanya. Other traits in less than 50% combinations showed a positive ultra-parent heterosis. The panicles per plant of only 19% combinations showed a positive ultra-parent heterosis. The average heterosis of the yield per plant in Sanya was higher significantly than in Harbin. The mid-parent heterosis of grain weight, the ultra-parent heterosis of grain weight, and the ultra-parent heterosis of panicle length per plant, grain numbers per panicle showed a high consistency between two pilot sites, but the heterosis in other yield traits is not consistent between two pilot sites.In two pilot sites, Non-additive effects and additive effects played important roles in affecting the yield traits, including grain yield per plant, panicle numbers per plant, grain numbers per panicle, panicle length per plant, grain weight. The additive effect was more important for grain number per plant and average panicle length per plant, and the genetic variance of grain number per plant and average panicle length per plant was mainly from non-additive effects in Harbin; the additive effects played an important role in affecting 5 yield traits in Sanya. It was not necessary that significant specific combining ability were detected in combinations from two parents with high general combining ability and the specific combining ability of combinations was difficult to predict only by the general combining ability of the parents. The general combining ability of traits with parents with high performance was high and the average of general combining ability was related with the performance of different traits in F1 generation in Harbin and Sanya.627 clear bands were amplified with 110 pairs of polymorphic primers for SSR. 562 of them showed a polymorphism and each pair of primers detected an average of 5.1 alleles. 896 clear bands were amplified with 63 pairs of polymorphic primers for SRAP. 327 of them showed a polymorphism and each pair of primers detected an average of 5.2 alleles. The numbers of bands amplified with SRAP primers was 1.4 times than with SSR primers. The average numbers of polymorphic sites were similar between two molecular markers. The genetic similarity was consistent between two molecular markers with the species of distant relationship and the results were consistent with distant relationship of the species. The performance of yield traits in F1 hybrid was related closely with the traits characteristics and the traits complementarity in their parents. However, the relationship between genetic distance and heterosis was not significant. The performance and the heterosis of yield traits were difficult to predict with SSR or SRAP molecular marker.The combinations with high heterosis and the combinations with low heterosis were clustered together in Harbin. However, the combinations with high heterosis were clustered together with high heterosis and the combinations with low heterosis were clustered together with low heterosis in Harbin. The average genetic diversity index, the average PIC in combinations with high heterosis was higher than the combinations with low heterosis in Harbin, but the average genetic diversity index, the average PIC in combinations with high heterosis was lower than the combinations with low heterosis in Sanya; the genome polymorphism was higher than in combinations with high heterosis than the combinations with low heterosis in Harbin, but the genome polymorphism in combinations with high heterosis was lower than in the combinations with low heterosis in Sanya.