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 (Pyre nopeziza brassicae) on winter oilseed rape were investigated in contro lled-environment experiments. The proportion of conidia which germinat ed on leaves, the growth rate of germ tubes, the severity of light lea f spot and the production of conidia increased with increasing tempera ture from 5 to 15 degrees C. The time to 50% germination of conidia an d the incubation and latent periods of light leaf spot lesions decreas ed 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 ra pe cultivars in the severity of light leaf spot, the production of con idia and the length of the incubation period but not in the length of the latent period. The responses to temperature for lesion severity an d incubation and latent periods appeared to be approximately linear ov er the temperature range 5-15 degrees C and could be quantified using linear regression analysis.