Parasitism of sedentary stages of Heterodera glycines by isolates of a sterile nematophagous fungus

Isolates of a sterile fungus designated ARF (Arkansas fungus) can be separa ted into two groups, ARF-C and ARF-L, that differ morphologically and in th eir ability to suppress numbers of Heterodera glycines on soybean. Our obje ctives were to determine if the two ARF groups differed in their ability to parasitize juveniles, females, and eggs in the rhizosphere of soybean and to proliferate in soil. The experiments were conducted in a greenhouse usin g soil infested with homogenized ARF mycelium. The ARF-L isolates parasitiz ed more juveniles and young females than did the ARF-C isolates. Suppressio n of these stages was 67% for ARF-L and 12% for ARF-C isolates 14 days afte r nematode inoculation. When soybean plants containing gravid females were transplanted into fungus-infested soil, ARF-L isolates parasitized 55 to 98 % of nematode eggs, whereas ARF-C isolates parasitized 0 to 22%. In both he at-treated and nonheated soil, the biomass of mycelial mats, a measure of r elative proliferation, tended to be greater for ARF-L than for ARF-C isolat es. The ability of ARF-L isolates to parasitize a large percentage of both prereproductive stages and eggs of H. glycines may contribute to its effect iveness as a biological control agent.