Variation Between Strains of the Nematophagous Fungus, Verticillium Chlamydosporium Goddard. I. Factors Affecting Growth in Vitro

Abstract

The growth and sporulation of six strains of Verticillium chlamydosporium isolated from Heterodera avenae eggs, were tested in vitro. Strains differed in their average growth rate, optimum temperature for growth, and production of chlamydospores. The optimal temperature for growth was 18°C for strains I, III, IV and V and appreciable growth occurred at 10°C but was slight at 5°C; strains II and VI grew best at 20 and 25°C. All strains grew well over a pH range 4-8 and there was little effect on hyphal growth at water potentials above -15 bars and only at - 80 bars did growth cease. Large numbers (up to 84 x 106/ml) of conidia, but not chlamydospores were produced in shaken liquid culture. Strains varied significantly in their pathogenicity to H. avenae eggs in tests on water agar; strain II was the most virulent at 12°C but grew fastest at 25°C. This strain readily produced chlamydospores on CMA and produced most propagules in liquid culture and may have potential as a biological control agent. The variation within V. chlamydosporium indicates that careful strain selection is essential in the development of this fungus for biological control.