Effects of yellow spot on wheat: comparison of epidemics at different stages of crop development

Abstract

Effects of yellow spot (Pyrenophoua tuitici-repentis) on two cultivars (Banks and Olympic) of wheat have been examined in a field experiment where distinctly different epidemics were produced in various treatments. Severe yellow spot before jointing reduced production of both tillers and dry matter, and substantially lowered leaf area index at jointing. Severe disease after jointing reduced leaf area index at flowering, dry weight of plants at maturity and harvest index. Crop phenology was also modified, with flowering being delayed by early disease and crop maturity hastened by late disease. Where yellow spot was severe throughout, the grain-filling period was greatly reduced. Grain yield of Banks was reduced by c. 13 % by early disease, c. 35 % by late disease, and c. 48 % by disease throughout the crop season. Most of the loss was in reduced grain size. Although yield loss in Olympic was less than in Banks, the resistance of Olympic was shown to be inadequate.