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Using sequence information from the mating type idiomorphs (<I>MAT-1</I> and <I>MAT-2</I>) of <I>P. brassicae</I>, the causal agent of light leaf spot of winter oilseed rape (<I>Brassica napus </I>ssp. <I>oleifera</I>), two PCR-based diagnostic assays were developed. The first assay was designed as a general diagnostic tool for <I>P. brassicae</I> and was shown to be specific, amplifying a 750 base pair (bp) product from genomic DNA from over 50 isolates of <I>P. brassicae</I> and not from DNA from a number of other fungal species pathogenic on oilseed rape or from the closely related discomycete <I>Tapesia yallundae</I>. The second assay was designed to differentiate between the two mating types (<I>MAT-1</I> and <I>MAT-2</I>) of <I>P. brassicae</I>, and was also specific to <I>P. brassicae</I>. Both assays were ale to detect the presence of <I>P. brassicae</I> from DNA extracted from oilseed rape leaves with light leaf spot symptoms. The sensitivities of both of the assays were increased by using templates consisting of mixtures of NDA from <I>P. brassicae</I> and <I>B. napus</I> compared with DNA from <I>P. brassicae</I> alone. Using a nested PCR approach, the sensitivity of the general diagnostic assay was increased by two orders of magnitude and it was able to detect the presence of <I>P. brassicae</I> prior to the development of visible symptoms on oilseed rape leaves. As a first step towards the development of an immuno-diagnostic tool for light leaf spot, the feasibility of adopting a targeted approach, combining molecular and immunological techniques, was investigated.

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Botrytis cinerea was systemically transferred into lettuce seeds by dry inoculation of the flower/bud with fungal spores. Plants grown from seeds were found to be systemically infected. Plants grown from infected seeds were used to investigate the behaviour of this systemic pathogen under different soil water saturations and the interaction of the pathogen with organisms at higher trophic levels. Variation in soil water saturation stressed the host plants resulting in a lower rate of photosynthesis, chlorophyll fluorescence and root weight. When the lettuce plants were infested with aphids (Myzus persicae) the rate of population growth of the aphids was slower on infected lettuce plants than uninfected plants. Numbers of lesions of B. cinerea were higher in aphid-free plants than on infested plants. Although the rate of chlorophyll fluorescence was not significantly affected by systemic B. cinerea and infestation with aphids, the effects of stress were evident in lettuce plants as the presence of aphids and 8. cinerea significantly affected the rate of photosynthesis, shoot and root weight of the plants. This confirms the interaction between two economically important pests of lettuce, the aphid Myzus persicae and the fungal pathogen, Botrytis cinerea. When the infested plants were attacked by the parasitoid Aphidius colemani, a greater number of M. persicae and their parasitoids were reared on lettuce plants free from infection by Botrytis cinerea. However, parasitoids attacked proportionally more aphids on uninfected plants, and both aphids and emerging parasitoids were significantly smaller when reared on infected plants. There was no difference in parasitoid sex ratio, with a 50:50 sex ratio found with parasitoids emerging from hosts reared on both infected and un infected plants. The results also revealed that the aphid hosts are larger when reared on plants free from B. cinerea infection than infected ones. In aphid hosts body size is a measure of host quality. The low number of parasitoid mummies recorded in aphids reared on B. cinerea infected plants indicated the negative effects of B. cinerea on both the preference and performance of the parasitoids. Experiments showed that learning has an influence on parasitoid host choice and that this is influenced by host plant infection status. These results show that the aphid M. persicae reared on uninfected plants when given a choice shows preference for uninfected plants while aphids grown on infected plants when given choice do not show a preference to either host. However, Aphidius colemani reared on aphids grown on uninfected plants but allowed to gain experience attacking aphids reared on infected plants showed a significant preference to the aphid hosts reared on infected plants when given a choice. While Aphidius colemani which emerged from aphids reared on infected plants but allowed to gain experience on hosts reared on uninfected plants showed a significant preference for the aphid hosts reared on uninfected plants when given a choice. Therefore, the behaviour of both host and parasitoid is affected by experience, and with the parasitoids, learning can alter host preference behaviour. The result from the field study confirmed the results of experiments done in a controlled environment room. Numbers of parasitoids were greater on exposed uninfected plants. Together, these results suggest that systemic infection by Botrytis cinerea may have considerable effects on ecological interactions at higher trophic levels.

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No description available.