Genetic Diversity And Differentiation Of The Wild Soybean(Glycine Soja Sieb.Et Zucc.) In China

Genetic diversity of wild soybean in China was analyzed at regional and local scales in this paper. Phenotypic diversity and evolution of phenotypic traits were investigated at the regional level by using the National Soybean Germplasm Database. Four wild soybean populations in Northern Huang Huai region of China were the targets for analysis of genetic diversity at local population level. Moreover, two cultivated populations were investigated in comparison with wild populations. We aimed to characterize genetic/epigenetic structures within and between cultivated and wild soybean at population level by two molecular markers AFLP and MSAP. The main results were as follows:6169wild soybean accessions were investigated focusing on phenotypic traits and diversity of different leaf shapes groups. The results showed that lanceolate leaves accessions had the highest genetic diversity. The frequencies of obvious main stem, gray pubescence, white flowers, non-sooty seed, yellow seed, brown hilum, high100-seed weight, low protein content and high oil content in round leaf were disproportionately high, while, line leaf accessions are primarily characterized by twining stems, brown pubescence, purple flowers, sooty seed, black seed, black hilum, low100-seed weight, high protein content and low oil content. Based on these results, we infer that, lanceolate and line leaves accessions tended to be wild types, while round leaf group represented more recently evolved accessions. Finally, accessions with ellipse, ovate-round and other leaves belonged to the intermediate evolutionary types. Our results suggest the evolution of leaf shape and other phenotypic traits, which is invaluable for efficient utilization and conservation of wild soybean.Phenotypic traits and diversity of different100-seeds weight groups were also analyzed. The mean protein content was the highest in1.22-2.71g type (46.02±3.20%), The mean oil content was the highest in0-1.21g type (9.04±1.68%), while the mean maturity time was the longest in0-1.21g type (144.39±30.39d).The qualitative traits, such as flowers color stem type、 seed coat color changed regularly with the increasing of100-seeds weight. Most researchers inferred that the accessions with big seeds in wild soybean represented more recently evolved types. Accordingly, variations of the characters significantly related to100-seeds weight represented the evolutionary transition from primitive to more recently evolved forms. For instance, from twining stems to obvious stems, from sooty to non-sooty seed coats, from purple to white flowers, from black to yellow seed coats, from low to high100-seed weight, from high to low protein content and from low to high oil content.By molecular marker AFLP, we evaluated genetic diversity and structure in the separate populations (named as AX, JZ, KL and WQ, respectively) of wild soybean in Huang Huai region of China. The results revealed that the genetic diversity index was the highest in the population WQ(I=0.287,PPL=68.62%), followed by the population AX(I=0.241,PPL=62.9%)、 KL(I=0.235,PPL=58.9%)and JZ (I=0.212,PPL=50.7%). AMOVA revealed that most of the genetic variation came from differences within populations, whereas only a small but significant portion(φst=0.291, P<0.010) of the variation was detected among populations. Through the Structure analysis, AFLP dataset yielded the optimal four clusters which reflected the geographical origin. In addition, The Bayesian population genomic scan of conventional AFLP loci data identified33outlier loci(2.3%of the total). The more outlier of AFLP loci data seemed to be responsible for the higher genetic differentiation which the AMOVA had evidenced.To understand the full significance of epigenetic variation in adaptive evolution, we evaluated epigenetic diversity by MSAP in the four populations of wild soybean mentioned above. The results showed higher epigenetic diversity were found in the four populations (Ne=1.290; I=0.280; He=0.178) which exceeded conventional genetic diversity within the wild soybean populations (n=130). AMOVA revealed the distribution of the epigenetic variation within and among populations (Ost=0.124, P<0.010) similar to the genetic one. Through the Structure analysis, MSAP data did not reveal the clusters expected to be differentiated clearly. In addition, The Bayesian population genomic scan of the MSAP loci data identified21outlier epi-loci(1.5%of the total) which is less than outlier loci. Consquently, genetic components in genome is the definitive factors in shaping population structure, and the selected epialleles were not strongly fixed in the populations as the genetic ones when divergent selection is weak. This will be evidence for the adaptive convergence of epigenetic in the same macroclimate.To characterize the genetic structure within and between cultivated and wild soybean populations in Huang Huai region of China, a total of124individuals were analyzed including94wild accessions and30cultivars by two molecular markers AFLP and MSAP. We found that the genetic diversity in the cultivated soybean exceeded that of wild soybean despite smaller sample sizes in cultivated populations(Cultivars, Ne=1.381,I=0.371, He=0.236; wild groups, Ne=1.278,I=0.270, He=0.171). The tendency was similar in the comparison of epigenetic diversity between the cultivated and wild soybean populations(Cultivars, Ne=1.384,I=0.365, He=0.235; wild groups, Ne=1.331,I=0.335, He=0.211). The reason for the greater amount of diversity in cultivated accessions could be due to gene flow by crossbreeding. In addition, the epigenetic diversity were significantly higher than the genetic diversity with using the same index in the three wild populations (F-test, P<0.001), however, the genetic and epigenetic diversity were differed slightly in the two cultivated populations (F-test, P=0.181-0.531). A possible explanation was that a fluctuating environment in natural habitats might lead to high level of variation in DNA methylation in wild populations. Finally,the Structure, AMOVA, and PCA analyses all revealed the presence of two genetically distinct species of wild and cultivated soybean (<Drt=0.12) and significant genetic differentiation between local wild populations (0.307<φst<0.352) on a small scale. This suggested the absence of gene flow between wild accessions and local cultivars, and among wild populations even on a small scale.