Geographical Distribution and Genetic Diversity of Soybean-Nodulating Bradyrhizobium spp. Isolated from Korean Soils

Abstract

Increasing world population have been made a various negative effect on earth environment, and the exhaustion of food is one of the serious problems in the future. In Korea, the consumption of soybean has been increased because of feeding to livestock, while the cultivation area and production of soybean have been decreased. To meet demand under limited conditions, effective and sustainable ways to enhance soybean production must be devised. Many other countries have been attempted to inoculate Bradyrhizobium spp. as the pro-environmental method to improve soybean productivity, but it was unprofitable because of specific interaction between the soybean cultivars and the indigenous Bradyrhizobium community. For the successful application of inoculum, the distribution of indigenous Bradyrhizobium spp. is necessary. The main objective of this study was to identify the geographical distribution of indigenous Bradyrhizobium spp. in cultivated soybean fields across Korea and compare the genetic diversity of each strain. A total of 268 Bradyrhizobium strains were isolated from 97 soybean samples (9 cultivars) collected in 14 regions. The Bradyrhizobium diazoefficiens was most dominant in the Korean soybean root nodule. Bradyrhizobium elkanii was predominated in the southwest region, meanwhile Bradyrhizobium diazoefficiens became dominant in northern regions. Depending on the result of PCA analysis and NMDS analysis, the high temperature and specific soybean cultivar affected the distribution of Bradyrhizobium elkanii in southern regions. The DNA fingerprint using rep-PCR shown the strain level of genetic diversity in each dominant strain. The genetic diversity of Bradyrhizobium spp. was affected by geographic location. Most of the strains isolated in the southern region and other regions of Korea were classified into different groups, respectively. Each strain of Bradyrhizobium sp. showed high genetic similarity in the same region, and the strains isolated from geographically close regions showed comparative high genetic similarity.