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Sibling plant pathogens can be grouped according to their host ranges into the following groups: group 1, sibling pathogens with nonoverlapping host ranges; group 2, sibling pathogens with both overlapping and nonoverlapping host ranges; and group 3, sibling pathogens with overlapping host ranges. Using the adaptive dynamics methodology, we investigated the evolution of sibling pathogens in relation to host specialization for groups 1 to 3. In particular, we focused on the role of multiple host niches and a trade-off in infectivity of pathogens to these hosts on the evolutionary outcome. We have shown that this ecological mechanism can explain only the evolution of sibling pathogens in group I and that other ecological and epidemiological mechanisms must be responsible for the evolution of sibling pathogens in the other two groups. [ABSTRACT FROM AUTHOR]

Effects of temperature on maturation of pseudothecia of Leptosphaeria maculans and L. biglobosa, closely related species which coexist on UK oilseed rape, were investigated. Stages in pseudothecial maturation on naturally infected oilseed rape debris were examined, both in controlled environments (5, 10, 15 or 20°C) under continuous wetness and in natural conditions (debris exposed in September and December 2000, and July, September and November 2002). Pseudothecia sampled weekly were assigned to maturation classes A (asci undifferentiated), B (asci differentiated), C (ascospores differentiated) or D (ascospores mature). Progress in pseudothecial maturation (assessed by time until 50% of pseudothecia reached each class) was similar for L. maculans and L. biglobosa at 15–20°C, but L. biglobosa matured more slowly at < 10°C. Maturation time decreased almost linearly with temperature from 5 to 20°C under continuous wetness but was longer in natural conditions, especially when periods of dry weather occurred. Differences in pseudothecial maturation are likely to contribute to epidemiological differences between L. maculans and L. biglobosa, which may explain their coexistence. It is appropriate to use the degree-day approximation to assess pseudothecial maturation at temperatures between 5 and 20°C, providing debris is wet. [ABSTRACT FROM AUTHOR]

Studies the progress with time of light leaf spot (Pyrenopeziza brassicae) on leaves of winter oilseed rape during the autumn in Great Britain, using a compartmental model. Differential equations used to describe the transition between compartments; Delay terms for the latent period between infection and sporulation.

Investigates the effects of stem canker and light leaf spot on yield of winter oilseed rape in southern England. Analysis on the relationship between yield loss and incidence or severity of stem canker; Combination of effects on several diseases on crop yield; Interaction between pests and diseases.

Investigates the effects of temperature and leaf wetness duration on conidial infection. Definition of the temperature and leaf wetness duration boundary; Assessment of light leaf spot; Effects of cultivar.

Less chocolate spot (% leaf area affected) developed on winter-sown field beans sprayed with benomyl than on untreated beans or beans sprayed with iprodione, prochloraz or thiabendazole. A single benomyl spray during flowering reduced disease development and increased yield by 20% in 1982 when a severe chocolate spot epidemic developed in untreated plots during flowering. Benomyl sprays at flowering also increased yield in 1980 when there was less disease at flowering in 1982, but did not increase yield in 1981 when there was little disease at flowering. In 1981 a severe chocolate spot epidemic developed early in the season and less chocolate spot developed on lower leaves of beans grown from seed treated with benomyl plus thiram than on beans grown from untreated seed. Treated plots yielded 70% more than untreated plots, although by early flowering there was no difference in chocolate spot between them. Seed treatment did not increase bean yields in 1982 and 1983, when chocolate spot did not develop early in the season. In the glasshouse, benomyl seed treatment prevented the development of aggressive lesions on lower leaves but thiram did not. [ABSTRACT FROM AUTHOR]