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

Abstract

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 208C, but not at 248C; spore pustules developed when the leaf wetness duration after inoculation was longer than or equal to approximately 6 h at 12±208C, 10 h at 88C, 16 h at 68C or 24 h at 48C. On leaves of cvs. Capricorn or Cobra, light leaf spot symptoms developed at 8 and 168C 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 168C when leaf wetness duration was 24 h, and increased to approximately 12 days as temperature increased to 208C and to 26 days as temperature decreased to 48C. At 88C, an increase in leaf wetness duration from 10 to 72 h decreased the latent period from approximately 25 to 16 days; at 68C, 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±168C, and decreased as temperature decreased to 88C or increased to 208C. At temperatures from 8 to 208C, 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.

Development of phoma lesions on oilseed rape leaves inoculated with ascospores of A‐group or B‐groupLeptosphaeria maculans(stem canker) at different temperatures and wetness durations

“…Analyses of data from these controlled‐environment experiments suggest that temperature is the main factor affecting the length of the incubation period ( t 1 or t 50 ) of both A‐group and B‐group L. maculans . Times to the appearance of the first leaf spot lesions and to the appearance of 50% of the lesions both decreased with increasing temperature from 5 to 20°C, suggesting that after ascospore infection, phoma leaf spot lesions will develop more rapidly in winter oilseed rape crops in autumn or spring than in winter, as with light leaf spot (Figueroa et al ., 1995; Gilles et al ., 2000). The results of the controlled environment experiments of Hammond et al .…”

Phylogenetic affinity of Mycochaetophora gentianae, the causal fungus of brown leaf spot on gentian (Gentiana triflora), to Pseudocercosporella-like hyphomycetes in Helotiales

“…Goodwin (2002) pointed out that the ecological features of Rhynchosporium and Ramulispora (=Helgardia) overlap; both pathogens cause eyespot on winter wheat and scald on barley, respectively, autumn through winter (Caldwell 1937;Fitt et al 1988), and their conidia are produced and germinate under low-temperature conditions (Caldwell 1937;Fitt et al 1988). Likewise, P. brassicae can infect its host and then produce new conidia at low temperatures (Gilles et al 2000). L. orchidicola has been isolated from plants growing in alpine and subalpine habitats in western Canada (Fernando and Currah 1995).…”

Modelling the progress of light leaf spot (Pyrenopeziza brassicae) on winter oilseed rape (Brassica napus) in relation to leaf wetness and temperature

“…Previous work on light leaf spot has produced information on the effects of temperature and wetness duration on the infection of oilseed rape leaves by P. brassicae conidia and the latent period in controlled environments, together with some validation of the results under field conditions (Figueroa et al ., 1995a, b; Gilles et al ., 2000a). According to these results, the minimum criterion for infection of leaves at 12°C and 18°C is a wetness duration of at least 16 h. Field experiments showed that the time from infection to sporulation (latent period) generally ranged between 150 and 250 degree‐days (accumulated mean daily temperature above zero).…”