Comparative Studies On Genetic Diversities Between In-situ Conserved And Non-conserved Oryza Rufipogon Populations In China

Oryza rufipogon Griff. is the ancestor of cultivated rice (Oryza sativa L.). It has many excellent genetic characters and genes. Previous field surveys showed that most populations of Oryza rufipogon were in the endangered status and needed to be conserved with a scientific and effective plan. In-situ conservation of Oryza rufipogon genetic resources has been proved to be an effective approach and well done in China. By the end of 2007, 15 Oryza rufipogon in-situ conservation sites had been established in different parts of China. However, these sites were selected mainly on the basis of the scientists'experience at national and provincial levels. Thus, the validity of the selected populations is still to be verified.With 24 pairs of SSR markers in rice, the research conducted genetic diversity analysis on 427 accessions of Oryza rufipogon from the fifteen in-situ conserved populations and 357 accessions from 15 non-conserved populations which were selected according to latitude, so as to study the genetic diversity and the representativeness of in-situ conserved Oryza rufipogon populations in all populations in China. Meanwhile in order to clarify the genetic diversity and relationship between populations of Oryza rufipogon in China and in Southeast Asia (including Vietnam, Laos and Cambodia), 85 individuals of Oryza rufipogon from Southeast Asia were analyzed. The results indicated that:1. Total 292 alleles were detected from all tested Oryza rufipogon Griff. populations in Chian with 24 SSR markers. The effective number of alleles per locus (Ae) was 6.63, the average Shannon-Weaver index (I) was 1.99, and the average expected heterozygosity (He) was 0.82. Among the SSR markers, RM252, RM250, RM280, RM289 and RM287 could detect more polyporphisms than the others.2. The average Ae and I of the 24 loci of the conserved populations were 5.98 and 1.90 respectively, both were higher than those of non-conserved populations (5.85 and 1.86 respectively). However, the average He of the 24 loci of the conserved populations was 0.79, which was lower than that of the non-conserved populations (0.80). Besides, the tests of significance on Ae, I and He of the SSR loci showed that there was no significant difference between the two groups, demonstrating that the genetic diversity of the conserved populations could be representative for the Oryza rufipogon populations in China. Moreover, the number of specific alleles of the conserved populations was 40, which far more than that of the non-conserved populations (20),showing that the conserved populations possessed more unique genes. In addition, based on previous research findings and in accordance with the geographic information of the conserved populations, the research results indicated that the 15 conservation sites cover all the typical geographic types of Oryza rufipogon habitats in China. Therefore, it could be concluded that the selection of the fifteen in-situ conservation sites were correct and reasonable.3. Based on the analysis of the genetic structure and cluster of the Oryza rufipogon populations in China, six groups were identified, among which 15 conserved populations distributed in four of the six groups randomly, but the other two grous did not have in-situ conserved populations. In accordance with the geographic information of the non-conserved populations, it could be found that most of the non-conserved populations were in the southern part of Guangxi and in Guangdong. Furthermore, based on previous research findings these areas were rich of genetic diversity of O. rufipogon in China and might be the original center of O. sativa. So it was recommended that future in-situ conservation sites should be established mainly in these areas.4. The cluster analysis for the populations from different parts of China and Southeast Asia (including Vietnam, Laos and Cambodia) showed that they originated from the same ancestor. Meanwhile, the main parameters of the genetic diversity of Oryza rufipogon in Southeast Asia were also high. The Oryza rufipogon from Southeast Asia might be valuable for use in rice genetic improvement.