INTERACTIONS BETWEEN HETERODERA-AVENAE AND PRATYLENCHUS-NEGLECTUS ON WHEAT

In a long-term field experiment, differential population densities of Heterodera avenae were produced by frequent cropping with resistant (c v. Panema) or susceptible (cv. Peniarth) oat. The two oat cultivars we re equally good hosts of Pratylenchus neglectus in a glass house exper iment with field soil. On wheat crops grown after oats in field experi ments, P. neglectus population densities in roots were higher in plots where H. avenae had been controlled than in plots with moderate infes tations (40 H. avenae eggs/g soil). The field observations indicated t hat the reduction in population densities of P. neglectus coincided wi th the development in roots of sedentary stages of the cyst nematode. Evidence for an indirect effect of H. avenae on P. neglectus was found in vitro in a split-root experiment. In the same field, grain yields of two wheat cultivars susceptible or resistant to H. avenae, but both susceptible to P. neglectus, was not reduced by P. neglectus. Alterna tion of H. avenae resistant and susceptible cultivars is a possible wa y of exploiting the inverse relationship between these nematodes, whil st controlling cyst nematode populations in intensive cereal productio n systems.