The infection of Heterodera avenae and H. schachtii eggs by six strains of Verticillium chlamydosporium on water agar was studied. Dead eggs and those that were immature were most readily colonised by all strains of the fungus. Strains differed in their pathogenicity but all were parasitic and capable of colonising viable eggs including those containing second-stage juveniles. Infection rates were no greater when hyphal growth around the eggs was stimulated by increasing the nutrient status of the agar medium, or when the eggs were surface sterilised. Eggs were more susceptible to parasitism within cysts and females of H. schachtii but not in those of H. avenae. In general, H. avenae eggs were more susceptible to parasitism than those of H. schachtii but strains differed in their virulence. The most likely strains to be effective pathogens of H. avenae eggs were I > II > VI whereas those for H. schachtii were V > I > VI. The method used was reliable in determining the relative pathogenicity of the six V. chlamydosporium strains in a number of experiments and could be used to screen large numbers of similar fungi for their potential as biological control agents.
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Kerry et al. (1986) studied this question.