Effect of nutrient level, pH and light on conidial germination in entomophthoraceous fungi

Abstract

Relative proportions of vegetative germination and of secondary spore formation were determined on agar substrata of different pH and nutrient status, in light and dark. Aphid pathogens and saprobes were included in the 7 species (11 strains) tested. With nutrient concentration exceeding a particular level (differing greatly according to the species), vegetative germination predominated at pH 5–8, while secondary spore formation predominated at pH 9–10. With nutrient levels below the appropriate threshold no common pattern of response to pH was found, and wide variation occurred, including germination exclusively by one mode little influenced by pH. No clear correlation was found between presumptive ecological niche and pattern of ermination. Aphid pathogens Entomophthora virulenta and Conidiobolus coronatus had very low nutrient ‘thresholds’ ( E. thaxteriana (0.75%) fell within the range 0.25–2.0% which included the presumed saprobes Basidiobolus ranarum , C. rhysosporus, C. brefeldianus and C. stromoideus . Light enhanced secondary spore formation in E. virulenta, B. ranarum, E. thaxteriana and C. stromoideus but had much less effect on the other species.