Exploring Basic Problems In Conservation Genetics Of Wild Soybean (Glycine Soja L.)

Conservation genetics is a new subject studying the conservation strategy that makes the nearly extinct or endangered species recover based on the profound knowledge of the genetic background of the species. The estimation of genetic diversity and the relationships between the spatial genetic structure and the mating system are important problems for long term consideration of most conservation geneticists. The wild soybean (Glycine soja), the predominantly self-pollinated species was used as materials to study and explore the problems. At the same time, the knowledge of the genetic background of the wild soybean is the prerequisite for the effective strategic conservation. The following studies had been carried out.(1) Using three molecular markers (AFLP, ISSR and SSR) to analyze genetic diversity of the wild soybean population in Shanghai Jiangwan district, different molecular markers were compared, and through computer randomly selected subsets with different sample size (5～90 individuals), the proper sample size was evaluated.(2) Genetic diversity of four wild soybean populations (JW-1, JW-2, BJ, and KL), were studying applying 17 SSR primers. Single genetic diversity index and the One-Parameter Index Families were calculated to exploring the effective methodologies that can be used to compare genetic diversity of different populations. Based on the spatial location of each individual, the spatial genetic structure of the four populations was analyzed, including the genetic differentiation and the fine-scale spatial genetic structure (FSGS).(3) Basing on 1605 progeny gotten from 36 families, the mating system of the four populations (JW-1, JW-2, BJ, and KL) were estimated by 5 SSR primers. Then according to the knowledge of genetic diversity, spatial genetic structure, and mating system of the four wild soybean populations, the conservation strategy was proposed.The following items were the main results:(1) More than 30 individuals were needed to reach 90% of the total genetic diversity of a population. For the small sample size, the unbiased estimation can be used to correct the statistical error.(2) Codominant molecular markers and the dominant molecular markers had different implication in explaining the genetic diversity and their genetic diversity indices range were different. So it was unreasonable to compare the results gotten by different molecular markers.(3) The single genetic diversity index can not reflect the allele frequency distributions, but one-parameter index family was a good substitution to evaluate genetic diversity.(4) There was a certain level of genetic differentiation among different wild soybean populations (F_st = 0.204), and there existed a considerable fine-scale spatial genetic structure (FSGS) within each of the four wild soybean populations; the mean Sp value was 0.073, ranging from 0.036 to 0.128, which implying the variation of the FSGS might be caused by the habitat heterogeneity and different levels of disturbances.(5) There were outcrossing events occurred in all the wild soybean populations and the mean outcrossing rate was 14.9%. Although the total outcrossing rate of these four wild soybean populations didn't have considerable disparity, the detail compositions of the outcrossing rates were divergent ( the KL population had the highest biparent inbreeding 63% and the JW-2 had the lowest only 6.7%).(6) Combining the results of the spatial genetic structure and the mating system, the conclusion can be drawn that the strength and the size of the FSGS had a deep effects on the mating system. The strong FSGS and large genetic patches may induced high level of biparental inbreeding, which reduced effective outcrossing rate.In general, a certain degree of disturbances to the natural habitats might be benefited for a plant population to maintain genetic variability and evolutionary potential, which has an important implication in strategic conservation of plant populations.