Antagonists of the cereal cyst nematode Heterodera avenae Woll. in Australian soils

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Abstract
Cereal growing soils of South Australia and western Victoria were surveyed for antagonists of second-stage juveniles and females of H. venae. Of eight species of fungi and two species of predacious mites isolated from soil, the only antagonists observed actually attacking H. avenae veniles were the nematophagous fungi Hirsutella rhossiliensis and Nematoctonus haptocladus. More than 23 000 females of H. avenae from 375 sites were examined over three years; about 1 % were diseased. The most widely distributed parasites were Verticillium chlamydosporium, Catenaria auxiliaris and an unidentified sterile fungus. Nematophthora gynophila, a fungus associated with the decline of H. avenae in England, was not found. However, when soil from England containing resting spores of N. gynophila was mixed with H. avenae infested soil from South Australia, females infected by the fungus were recovered. Both C. auxiliaris and the unidentified sterile fungus were found only in fine textured soils in wetter districts, and were more active during the 1979-80 wet season than the following two dry seasons. V. chlamydosporium was found throughout the sampling area and was not confined to soils which were frequently moist, or to soils of a particular texture. Its population densities were generally low (less than 50 chlamydospores/g). The possible use of fungi parasitic on H. avenae for biological control of the nematode in Australia is discussed.