Baseline sensitivity to three triazole fungicides in Pyrenophora tritici-repentis

Abstract

Pyrenophora tritici-repentis (anamorph: Drechslera tritici-repentis) causes yellow spot of wheat. The disease can be responsible for yield losses of 30–50% and, when severe, requires management with fungicide. Forty-five single conidium isolates collected from the northern wheatbelt of Western Australia were tested for sensitivity to three triazole fungicides in culture. At 0.2 mg/mL epoxiconazole and 0.4 mg/mL propiconazole and tebuconazole, the mean relative diameter of cultures was close to 50%, indicating that epoxiconazole had about twice the in vitro activity of propiconazole or tebuconazole. Isolates exhibited a significant fungicide rate interaction such that some isolates differed in response to propiconazole compared with epoxiconazole or tebuconazole. Sensitivity among 32 isolates collected from commercial wheat crops over the period 2001–03 was not significantly different from sensitivity among 13 isolates collected in 1986–87 when fungicide use was minimal. The observed EC₅₀ values (concentration of fungicide required to cause 50% inhibition of growth of isolates) provide a basis to monitor potential changes in sensitivity to azole fungicides.