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

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 of Hirsutella minnesotensis against soybean cyst nematode (SCN) Heterodera glycines was 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 x 10(7) fg (g soil)(-1) after inoculation, subsequently decreased rapidly until 28 days (1.34 x 10(4)-1.51 x 10(4) fg (g soil)(-1)), then remained constant in SCN-free soil. While it decreased rapidly up to 14 days (around 1.40 x 10(4) fg (g soil)(-1)), it then varied with the population changes of SCN over time. The amount of H. minnesotensis DNA was highest in the rhizosphere soil with both H. minnesotensis and SCN incubation. The percentage of nematodes parasitised was positively correlated with the amount of H. minnesotensis DNA in soil with soybean. Microscopic observations indicated that H. minnesotensis could colonise the surface of soybean roots. In addition, H. minnesotensis inoculation significantly improved the biomass of soybean. Therefore, the rhizosphere colonisation, relationship between SCN parasitism and fungal density, and growth promotion of soybean support H. minnesotensis as a potential biocontrol agent.