Population dynamics and biocontrol efficacy of the nematophagous fungus Hirsutella minnesotensis in pot assay

Abstract

Monitoring the population dynamics of a biocontrol agent and its target pest in soil is fundamental to the understanding of the mechanisms of biocontrol. In this study, the population dynamics and the control efficacy ofHirsutella minnesotensisagainst soybean cyst nematode (SCN)Heterodera glycineswas studied using quantitative real-time polymerase chain reaction (qPCR), confocal laser scanning microscopy and bioassay in sterilised soil. The qPCR test revealed that the amount of DNA was 1.12 × 107fg (g soil)−1after inoculation, subsequently decreased rapidly until 28 days (1.34 × 104-1.51 × 104fg (g soil)−1), then remained constant in SCN-free soil. While it decreased rapidly up to 14 days (around 1.40 × 104fg (g soil)−1), it then varied with the population changes of SCN over time. The amount ofH. minnesotensisDNA was highest in the rhizosphere soil with bothH. minnesotensisand SCN incubation. The percentage of nematodes parasitised was positively correlated with the amount ofH. minnesotensisDNA in soil with soybean. Microscopic observations indicated thatH. minnesotensiscould colonise the surface of soybean roots. In addition,H. minnesotensisinoculation significantly improved the biomass of soybean. Therefore, the rhizosphere colonisation, relationship between SCN parasitism and fungal density, and growth promotion of soybean supportH. minnesotensisas a potential biocontrol agent.