Some effects of climate and plant growth on the development of light leaf spot in cauliflowers

Abstract

In laboratory and climate chamber studies with Pyrenopeziza brassicae Sutton and Rawlinson, most conidia germinated at l6°C, mycelial growth was most rapid (about 1 mmjday) over the range 15–20°C, and symptom development on cauliflower leaves was greatest at 18°C. High relative humidity (98–100%) was required for conidial germination but symptom development was inversely proportional to atmospheric saturation. Results of field studies are discussed in the light of these findings. Conidia rarely germinated on newly emerged leaves, but the proportion germinating increased as the leaves expanded and was optimum on fully expanded leaves. Symptoms did not usually appear on leaves during the early stages of leaf expansion.