Abstract: Metarhizium anisopliae, an entomopathogenic fungus, has been applied as a biocontrol agent to control soil-dwelling pests. The mass release of the fungus may change native microbial communities and impact the comprehensive effect of plant protection. In this paper, we investigated the population dynamic of applied M. anisopliae and native microbes including bacteria, fungi and actinomycetes in the soil of rhizosphere and root bulk after M. anisopliae treatment in peanut sowing period. The results showed that the applied M. anisopliae rapidly decreased within 30 days, then slowed down and continued to survive at low density. With peanut growing, the soil microbes exhibited their own process of ascending-and-descending population. In comparative, the applied M. anisopliae caused a greater influence on actinomycetes than on fungi, and minimal impact on bacteria. The effect on soil microorganisms was greater in rhizosphere than in root bulk. Separately, the M. anisopliae treatment had no significant effect on the bacteria in rhizosphere and root bulk as well as fungi in root bulk. However, the treatment slowed down the initially declining rate of fungal population in rhizosphere, that delayed the time to reach the bottom from 15 d to 30 d but after then accelerated the recovery rate. The peak was advanced from 60 d to 45 d but only reached 2/3 height of the control peak. For actinomycetes, M. anisopliae significantly inhibited the actinomycete population in the rhizosphere, making its fluctuation completely opposite to that of the control, and it did not rise again after falling to the low point on 45 days. In the soil of root bulk, M. anisopliae slowed down the declining rate of actinomycete population that delayed the time to reach the bottom from 30 d to 45 d and reduced the following recover numbers. The community structure of soil microbial was changed significantly in 15 d and 30 d after M. anisopliae treatment. The control proportion of bacterial population decreased significantly during this period. However, compared with the control, the proportion of rhizospheric bacteria increased and the proportion of fungi decreased, while the proportion of actinomycetes was significantly reduced first and then increased. The community structure was less varied in the root bulk. After 45 d, during peanut flowering, podging and maturity, the communities gradually recovered to the original state.

Key words: Metarhizium anisopliae, soil microbes, population dynamics, persistence, peanut