| Nematophagous fungi Hirsutella minnesotensis and Hirsutella rhossiliensis are two endoparasites of second-stage juveniles (J2) of the soybean cyst nematode (SCN), Heterodera glycines. Ecology and biology of the two fungi were investigated in laboratory and greenhouse and Minnesota soybean field. Hirsutella minnesotensis is a recently isolated pathogen of the SCN. The fungus started sporulation 7 days after inoculation (DAI), and the number of spores on the mycelium reached a peak, average 39 (range 5 to 120) spores/J2, at 13 or 14 DAI. After the peak, the number of spores on the mycelium decreased quickly. At 38 DAI, only a few or no spores were observed on the mycelium. On water agar test, spores detached from phialides appeared to lose infectivity. However, when the detached spores and J2 were incubated in soil for two days, there were 7.5% to 9.7% of the J2 attached by fungal spores. The percentage of J2 transmitted by the fungus was positively related with the number of fungus-colonized J2 initially added into the soil. At 4,800 fungus-colonized J2 (= 72,000 spores) per 25 grams of soil, approximately 75% of assay J2 were transmitted 9 days after adding the colonized J2. The fungus has a weak ability of saprophytic growth in soil. Mycelium or spores added into soil could produce infective spores initially, but parasitism declined over time, and at 35 days after adding the fungus only limited parasitism was observed by adding assay J2. When fungus-colonized J2 were added into soil treated with microwave heating, infective spores were detected up to 367 days, but no infectivity was observed at 450 day after adding the J2. Nematode host range of H. minnesotensis was wide including plant-parasitic nematodes, entomophilic nematodes, fungal-feeding nematodes, and bacteria-feeding nematodes.In greenhouse studies, both liquid culture at 0.2, 0.4 and 0.8 g of mycelium/pot and solid culture at 1% of corn-grits culture of the two fungi effectively reduced nematode population densities in both autoclaved and untreated soils. Four soils with different pH, texture and organic matter influenced parasitism of J2 and biocontrol effectiveness of the two fungi.The effect of pH on growth and sporulation Hirsutella rhossiliensis and Hirsutella minnesotensis on agar plate was investigated. The optimum pH for the colony to grow on agar was approximately 6.2 for both fungi. The growth of both species was reduced drastically when pH was reduced to 4, and reduced gradually when pH increased from the optimum pH up to pH 10. Optimum pH for sporulation of the two fungi was similar to the optimum pH for growth, and the sporulation was greatly inhibited by either low pH at 4 or high pH at 9 and 10.The effect of tillage on parasitism of Heterodera glycines J2 by the two fungi was investigated in soybean and corn fields in Minnesota during 2002 and 2003. Two years data indicated that there were no differences between conventional tillage and no-till for the parasitism of Hirsutella spp. at the different sampling dates either in soybean field or corn field in 2002. In 2003, however, the percentage of J2 parasitized by Hirsutella in no-till was significantly higher than that in conventional tillage in spring and at harvest in the soybean field. In soybean field, the percentage of J2 parasitized by Hirsutella spp. was higher than that in corn field. The seasonaffected the parasitism of the fungus Hirsutella spp.; the percentage of J2 parasitized by Hirsutella spp. at middle season was higher than that at planting and harvest season.On water agar and soil tests, H. rhossiliensis and H. minnesotensis were able to infect and colonize root, but symptoms of root disease were not observed. Hirsutella rhossiliensis promoted soybean growth in autoclaved soil and natural soil, however, H. minnesotensis only promoted soybean growth in autoclaved soil.
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