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

Abstract

<i>Radix pseudostellariae</i> is a perennial tonic medicinal plant, with high medicinal value. However, consecutive monoculture of this plant in the same field results in serious decrease in both yield and quality. In this study, a 3-year field experiment was performed to identify the inhibitory effect of growth caused by prolonged monoculture of <i>R. pseudostellariae</i>. DGGE analysis was used to explore the shifts in the structure and diversity of soil <i>Fusarium</i> and <i>Pseudomonas</i> communities along a 3-year gradient of monoculture. The results demonstrated that extended monoculture significantly boosted the diversity of <i>Fusarium</i> spp., but declined <i>Pseudomonas</i> spp. diversity. Quantitative PCR analysis showed a significant increase in <i>Fusarium oxysporum</i>, but a decline in <i>Pseudomonas</i> spp. Furthermore, abundance of antagonistic <i>Pseudomonas</i> spp. possessing antagonistic ability toward <i>F. oxysporum</i> significantly decreased in consecutively monocultured soils. Phenolic acid mixture at the same ratio as detected in soil could boost mycelial and sporular growth of pathogenic <i>F. oxysporum</i> while inhibit the growth of antagonistic <i>Pseudomonas sp</i>. CJ313. Moreover, plant bioassays showed that <i>Pseudomonas</i> sp. CJ313 had a good performance that protected <i>R. pseudostellariae</i> from infection by <i>F. oxysporum.</i> In conclusion, this study demonstrated that extended monoculture of <i>R. pseudostellariae</i> could alter the <i>Fusarium</i> and <i>Pseudomonas</i> communities in the plant rhizosphere, leading to relatively low level of antagonistic microorganisms, but with relatively high level of pathogenic microorganisms.