Fungal parasite of cereal cyst-nematode heterodera-avenae

Abstract only no further text Heterodera avenae is a widespread root parasite of oats, wheat and barley, and is particularly damaging on free-draining soils. The continuous cropping of cereals on the same land is now common practice. Much of this land is infected by the nematode but H. avenae populations often fail to increase when hosts are grown continuously. In soils where numbers do not increase the nematode completes its life-cycle but many females fail to form cysts, probably because they are parasitized by fungi which kill them and their eggs. An Entomophthora-hke fungus is the most widespread parasite and has not previously been recorded from nematodes. The hyphae ramify throughout the body tissues of the female nematode before the much-branched mycelium breaks up into hyphal bodies. These hyphal bodies give rise to thick-walled resting spores and diseased females are filled with up to 4000 of these spores; the nematode cuticle being destroyed leaving a soft spore mass. The hyphal bodies may also give rise to thin tubes which penetrate the disrupted cuticle and protrude into the soil. The cytoplasm within these tubes rounds off to produce spherical, thin-walled conidia which are thought to be the non-motile, infective stage. The mycelial growth and resting spore production is similar to that in members of the genus Entomophthora, which contains the insect parasitic fungi, but conidial formation is atypical. The life-cycle of the fungus takes 4 days at 12 °C; all infected females disintegrate and dis- appear from the root surface in 9 days. High levels of fungal parasitism are associated withpoor nematode egg production and fungi appear to be a major factor in limiting the repro- duction of this nematode.