Fungi and the Decrease of Cereal Cyst-nematode Populations in Cereal Monoculture1

Populations of the cereal cyst-nematode decrease when cereals are grown frequently or continuously because the females that develop on the roots between May and July fail to produce eggs, or produce a smaller number than expected. Consequently, cysts in the soil after harvest are fewer and contain fewer eggs. The role of fungal parasites and competitors in limiting populations of cyst-nematodes is reviewed. Parasites of eggs and females of Heterodera avenae Woll. were widespread in British cereal fields, an Entomophthora-like fungus and Verticillium chlamydosporium Barron & Onions being the most common species found. Although fungal parasites may be the cause of the failure of the nematode to increase, it has not yet been established unequivocally.