The development of eyespot on stems of winter wheat and winter barley in crops inoculated with W-type or R-type isolates of Pseudocercosporella herpotrichoides

Abstract

In three contrasting seasons (1986-1988), W-type isolates of Pseudocercosporella herpotrichoides generally became established on stems of winter wheat or winter barley plants more rapidly than did R-type isolates. After growth stage (GS) 30/31, eyespot lesions became visible on stems more quickly, and by GS 71 both the incidence and severity of stem lesions were generally greater in plots inoculated with W-type isolates than in plots inoculated with R-type isolates. However, by harvest there was little difference in eyespot incidence or severity between W-type and R-type plots in 1987 or 1988; in 1986, the difference was maintained until harvest. In 1986, the winter was cold and basal leaf sheaths of wheat died quickly in the spring; a severe eyespot epidemic did not develop although the leaf sheaths of many plants were severely infected at GS 30/31. However, the incidence and severity of eyespot were greater in early-sown than in late-sown plots. In 1987, the winter was mild and basal leaf sheaths of wheat and barley did not die rapidly. The leaf sheath severity score was 3-4 at GS 30/31 and thereafter P. herpotrichoides steadily penetrated the remaining leaf sheaths and became established on the stem so that a severe epidemic had developed by GS 71. In 1988, when the crops were late-sown and the winter mild, a late severe epidemic developed even though the leaf sheath severity score was only 1-3 at GS 30/31. On barley in 1987, the differences between W-type plots and R-type plots were greater than on wheat, but in 1988 there were few consistent differences. The effects of seed rate on eyespot incidence and severity were not significant in 1987 or 1988, although eyespot was generally less at the low than the high seed rate.