Fungal Parasites of the Cereal Cyst Nematode Heterodera avenae in Southern Sweden

Fungal parasites of the cereal cyst nematode Heterodera avenae were isolated from four sites in southern Sweden. In all, 15 different fungi were isolated from different stages of the nematode life cycle. Among the egg parasites, Verticillium chlamydosporium was common in young cysts on roots, whereas an unidentified species of Verticillium (Verticillium sp. 1) was the dominating species in cysts from soil, especially if the soll had been stored for 8-12 months. V. chlamydosporium was frequently isolated from eggs in cysts from soil, when analyzed shortly after sampling. Verticillium sp. 1 is distinct from V. chlamydosporium because it does not produce dichtyo-chlamydospores in the aerial mycelium and because it grows at 6 C where V. chlamydosporium fails to grow. Paecilomyces lilacinus, Microdochium bolleyi, Cylindrocarpon sp., and several nonsporulating fungi were also isolated from eggs in cysts from soil. Between 10 and 20% of the eggs in cysts collected in the field were infected with fungi. In a pot test between < 1 and 29%, with a mean of 13%, of females on roots became infected, always by Nematophthora gynophila. Resting spores of N. gynophila extracted directly from field soil, collected at the four sites, varied from 3 to 49 spores/gram of air dried soil.