The effect of variety mixtures on the development of swede powdery mildew

Abstract

Infection by Erysiphe polygoni was followed on the components of five mixed populations containing different proportions of a partially resistant swede variety, Ruta Øtofte (RØ), and a highly susceptible variety, Ne Plus Ultra (NPU) (100:0; 75:25; 50:50; 25:75; 0:100). Disease levels remained much lower on RØ than on NPU in all populations. For several weeks, disease on NPU was greatest in pure plots and was progressively reduced in mixtures with increasing proportions of RØ. Later, disease levels on NPU were similar in all populations. Disease on RØ was not increased in mixtures with NPU. Root yield of NPU, but not of RØ, was greater in mixtures than in pure stands. The possible use of variety mixtures to control powdery mildew in swede crops is discussed.