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.Peer reviewe

Effects of temperature and wetness duration on conidial infection, latent period and asexual sporulation of Pyrenopeziza brassicae on leaves of oilseed rape

Experiments in controlled environments were carried out to determine the effects of temperature and leaf wetness duration on infection of oilseed rape leaves by conidia of the light leaf spot pathogen, Pyrenopeziza brassicae. Visible spore pustules developed on leaves of cv. Bristol inoculated with P. brassicae conidia at temperatures from 4 to 20 degrees C, but not at 24 degrees C; spore pustules developed when the leaf wetness duration after inoculation was longer than or equal to approximately 6 h at 12-20 degrees C, 10 h at 8 degrees C, 16 h at 6 degrees C or 24 h at 4 degrees C. On leaves of cvs. Capricorn or Cobra, light leaf spot symptoms developed at 8 and 16 degrees C when the leaf wetness duration after inoculation was greater than 3 or 24 h, respectively. The latent period (the time period from inoculation to first spore pustules) of P. brassicae on cv. Bristol was, on average, approximately 10 days at 16 degrees C when leaf wetness duration was 24 h, and increased to approximately 12 days as temperature increased to 20 degrees C and to 26 days as temperature decreased to 4 degrees C. At 8 degrees C, an increase in leaf wetness duration from 10 to 72 h decreased the latent period from approximately 25 to 16 days; at 6 degrees C, an increase in leaf wetness duration from 16 to 72 h decreased the latent period from approximately 23 to 17 days. The numbers of conidia produced were greatest at 12-16 degrees C, and decreased as temperature decreased to 8 degrees C or increased to 20 degrees C. At temperatures from 8 to 20 degrees C, an increase in leaf wetness duration from 6 to 24 h increased the production of conidia. There were linear relationships between the number of conidia produced on a leaf and the proportion of the leaf area covered by 'lesions' (both log(10)-transformed) at different temperatures.Peer reviewe