Assessment of the Diversity of Pseudomonas spp. and Fusarium spp. in Radix pseudostellariae Rhizosphere under Monoculture by Combining DGGE and Quantitative PCR

Radix pseudostellariae is a perennial tonic medicinal plant, with high medicinal value. However, consecutive monoculture of this plant in the same field results in serious decline in both yield and quality. In this study, a three-year field experiment was conducted to determine typical growth inhibition effects caused by extended monoculturing of R. pseudostellariae. DGGE analysis was used to explore the shifts in the structure and composition of soil Fusarium and Pseudomonas communities along a three-year gradient of monoculture. The results indicated that prolonged monoculture significantly increased the diversity of Fusarium spp., but decreased Pseudomonas spp. diversity. Quantitative PCR analysis showed a significant increase in F. oxysporum, but a decline in Pseudomonas spp. Furthermore, abundance of antagonistic Pseudomonas spp. with antagonistic activity against F. oxysporum was lower in extended monoculture soils. Phenolic acid mixture at a ratio similar to that found in the rhizosphere could promote mycelial growth of pathogenic F. oxysporum while inhibiting the growth of antagonistic Pseudomonas sp. CJ313. Moreover, plant bioassays showed that Pseudomonas sp. CJ313 had a good performance that protected R. pseudostellariae from infection by F. oxysporum. In conclusion, this study demonstrated that extended monoculture of R. pseudostellariae could alter the Fusarium and Pseudomonas communities in the plant rhizosphere, leading to relatively low level of antagonistic microorganisms, but with relatively high level of pathogenic microorganisms.