Invasion and development of the cereal cyst‐nematode Heterodera avenae in roots of barley infected by the take‐all fungus Gaeumannomyces graminis

SUMMARY Observations on the invasion and development of Heterodera avenae in relation to take‐all infection of barley roots were made in three pot experiments. Post‐cropping H. avenae populations were lower on fungus‐infected plants, as a result of the production of fewer, smaller and less fecund cysts. The reduction in cyst numbers was associated with reduced larval invasion of take‐all infected roots and with the effects of the unfavourable environment of these roots on female development, possibly through its effects on sex determination and survival of the larvae.