EFFECTS OF TEMPERATURE ON THE DEVELOPMENT OF LIGHT LEAF-SPOT (PYRENOPEZIZA-BRASSICAE) ON OILSEED RAPE (BRASSICA-NAPUS)

The effects of temperature on the development of light leaf spot (Pyrenopeziza brassicae) on winter oilseed rape were investigated in controlled-environment experiments. The proportion of conidia which germinated on leaves, the growth rate of germ tubes, the severity of light leaf spot and the production of conidia increased with increasing temperature from 5 to 15 degrees C. The time to 50% germination of conidia and the incubation and latent periods of light leaf spot lesions decreased when temperature increased from 5 to 15 degrees C. At 20 degrees C, however, light leaf spot severity and production of conidia were less and the incubation and latent periods were longer than at 15 degrees C. There were differences between P. brassicae isolates and oilseed rape cultivars in the severity of light leaf spot, the production of conidia and the length of the incubation period but not in the length of the latent period. The responses to temperature for lesion severity and incubation and latent periods appeared to be approximately linear over the temperature range 5-15 degrees C and could be quantified using linear regression analysis.