Observations On Fungal Parasites of Females and Eggs of the Cereal Cyst-Nematode, Heterodera Avenae, and Other Cyst Nematodes

Most populations of the cereal cyst-nematode are parasitised by fungi killing females and eggs. The life history of an Entomophthora-like fungus, which kills females and causes the breakdown of the cuticle preventing cyst formation, is described. This fungus attacks other cyst-nematodes but not Globodera rostochiensis. A method is described for estimating the number of diseased eggs in females and cysts. Verticillium chlamydosporium was the most frequently observed egg parasite; it killed 50% of the eggs in females on barley roots in July in a field trial. Tarichium auxiliare and Cylindrocarpon destructans were found more frequently in soils where the nematode failed to multiply than in those where it increased but were not considered important as few females were infected. Similar numbers of new females were produced in soils where populations multiply or decline but in decline soils many failed to form cysts and few healthy eggs were produced.