| Indica-japonica hybridization is an important rice breeding method, aimed at taking advantage of favorable genes in different subspecies. To date, great achievements have been obtained in the wide study on classification, origin, and develpment of Asian cultivated rice and indica-japonica hybridization breeding. Based on above, this study uses F2, F3, and F6generations population from crossing of typical indica QiShanZhan and japonica Akihikari as the materials, which are grown in Liaoning (japonica area in Northeast China) and Guangdong(indica area in South China) province, respectively. Begining at F2generation, populations are harvested by single-seed descent (SSD), bulk harvesting (BM), and pedigree methods (PM). Using morphological marker (Cheng’s Index) and molecular markers (InDels and ILPs), a comparative study has been made on the differences between morphological and genetic differentiation, and economic traits in different environments. In addition, this study also identifies the law of subspecies differentiation in filial generation of indica-japonica hybridization, and its relationships with economic traits under different environments; reveal the genetic basis on the effect of natural and artificial selection on subspecies differentiation; explores how to estimate indica-japonica adaptability of different environments, using the relationship between subspecies differentiation and economic traits; and finally, provides new insights into the process of subspecies differentiation to improve the efficiency of indica-japonica hybridization breeding, and inform to carry out" changing indica to japonica" project.1. In early generations, subspecies characteristics of all population show the normal distribution and continuous variation, and no distortion segregation is found between two environments of F2population and F3SSD populations, and F2and F3SSD population. However, there are significant differences and obvious phenomenon of distortion segregation between two environments of F3BM population, SSD and BM population of F3generation, and F2and F3BM population. In addition, it is found that the results classified by Cheng’s Index are in accordance with those classified by molecular markers, whether in different environments or seed harvesting methods. Furthermore, there are also significant correlations with distribution of japonica kinship percentage (Dj) found in glume pubescence (GP), length of the first and second panicle internodes (LPI), length-width ratio of grains (LWR), and Cheng’s Index.2. In F6generation, populations also show a normal distribution and continuous variation. According to comparing the population distribution of different environments, it is found that there’s no difference in SSD populations (p=0.93), a minute but non-significant difference in BM populations (P=0.40), a significant difference in PM populations (P=0). And the whole PM populations are indica-deviated; moreover, PM population in Guangdong is more indica-deviated than that in Liaoning. Besides, in BM and SSD population, there’s a discontinuous variation from indica-deviated or japobica-deviated individuals to neutral kinship individuals in frequency distribution; the most majority of individuals are neutral kinship (Dj=40%-60%), but few is indica-deviated or japonica-deviated (Dj>60%or<40%). This phenomenon suggests that there are potentials existing in indica-japonica hybridization breeding.3. Drawing on the study on changes of subspecies characteristics, LPI is found to be closely related with morphological subspecies differentiation, probably as a effective index of morphological classification; but glume color (GP) has a close relationship with subspecies differentiation in molecular level, probably as an accessory index in morphology for subspecies genetic differentiation; additionally LWR is closely related with subspecies differentiation both in morphological and molecular level, possibly as an effective classification index to indicate the changes of subspecies in the process of differentiation. In addition, LWR also shows great differences between Liaoning and Guangdong provinces, demonstrated to has a fast response to environment, which implies that LWR is probably affected by epigenetics.4. According to the study on the relationships between subspecies differentiation and economic traits,1000-grain weight (KW) is related to subspecies characteristics and shows japonica type>japonica-deviated type> indica-deviated type> indica type; and the kinship in the region of grain weight and shape genes with respect to KW is significantly and positively correlated with Dj; but seed setting rate (SSR) and grain yield per plant (GYP) are related with ecological adaptability, because correlation results show that their performance of japonica type is better than indica type in Liaoning but it is opposite in Guangdong; in F6generation, not only grain shape and weight genes are related to subspecies differentiation but some other genes with respect to plant type, panicle type, and heading date et al. are also significantly correlated with subspecies differentiation.The results above demonstrate that genetic recombination could not cause distortion segregation; and environment could affect the speed of stabilization on different kinship individuals, which is the performance of ecological adaptability; and in the process of population differentiation, selection and elimination effect of environment are weak, which could not significantly affect population differentiation and cause distortion segregation. However, artificial selection is found as the main factor obviously causing distortion segregation in filial generation from indica-japonica hybridization, with the effect of nature selection and ecological adaptability. In addition, it is also found that there’s close relationship between subspecies differentiation and some important agronomic traits. Especially in grain shape and weight, they show a close relationship whether in traits performance or correlation. This may be the primary cause resulting in why indica-japonica hybridization breeding didn’t achieve the required effect of combining subspecies superiority but subspecies kinship. |
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