Analysis of rhizosphere microbial community structure of weak and strong allelopathic rice varieties under dry paddy field

Terminal restrain fragment length polymorphism (T-RFLP) technique was employed to investigate the microbial community structure and composition in the rhizosphere of weak and strong allelopathic rice varieties directly sowing on dry paddy field at 5-leaf stage and 7-leaf stage. The results showed that 9--87 TRFs and 15--89 TRFs were detected from the soil DNA digested with two restriction enzymes Hae III and Msp I, respectively. The rank-abundance of TRFs from different samples showed extremely significant difference, indicating that relative abundance of rhizosphere bacteria was markedly different. The diversity indices including species abundance (S), Shannon-wiener diversity index (H), Pilow diversity index (D) and evenness index (E) were used to analyse the diversity of TRFs in 6 samples. The analysis of correlation coefficients among species indices showed that Shannon-wiener diversity index was the best one for the investigation of the species diversity. The Shannon-wiener diversity in the sample of PI7 was the highest compared with those in the others. The cluster analysis and principle analysis suggested the similarity among the 3 samples of 5-leaf stage was greater than that of 7-leaf stage. Especially, the three samples of 7-leaf stage were separated by not only principal component I but also principal component II, which implicated that the composition and structure of soil microorganism community could be regulated by both growth stage of rice and rice variety. The Shannon-wiener diversity index and species richness of PI7 were the highest in all samples, and 34 genera were special in PI7, in which 7 genera belonged to myxobacteria. Some sliding bacteria and N-fixing bacteria were also found in those special genera of PI7. Secondary metabolites of Myxobacteria might improve the allelopathic potential of allelopathic rice by inhibiting germination of weed seeds in soil seed bank and decreasing the density of weeds in the field of rice.