Sclerotinia sclerotiorum is a necrotrophic fungal pathogen with a worldwide distribution and a wide host range, including many economically important crops. The control strategies for this pathogen and related species include using fungicides, biological control agents and cultural practices such as crop rotations. However, the genetic diversity and the long term survival structures (sclerotia) of this pathogen, combined with the recent discovery of the related species S. subarctica in England and the need for growers to implement integrated disease management strategies means that new control measures need to be sought. Biofumigation, using green manures which are macerated and ploughed into the soil, may be a useful new control approach in an integrated programme. Microcosm and in vitro experiments clearly showed that volatiles released from biofumigation crops have a direct inhibitory effect on the mycelial growth and carpogenic germination of S. sclerotiorum sclerotia. The most effective biofumigation crop for inhibiting carpogenic germination varied depending on whether the volatiles released from the biofumigant crops were in direct contact with the sclerotia when the most effective crop was Raphanus sativus ‘Terranova’, or in the vapour phase when the most effective crop was B. juncea ‘Vittasso’. Carrot root inoculations showed that the number of sclerotia produced on carrot roots was significantly affected by S. sclerotiorum isolate. However, the results also showed that the weight of individual sclerotia produced by different isolates was influenced by carrot accession, but not by S. sclerotiorum isolate. Additionally, the carrot plant and detached leaf inoculations showed significant differences in the rate of lesion progression of S. sclerotiorum on different carrot accessions, indicating differences in susceptibility to the pathogen. S. subarctica microsatellite haplotypes identified in this research were shown to be shared between Scotland and Norway, and between crop plants and meadow buttercup. However, the English population did not share any microsatellite haplotypes with any other population, and analysis indicated that this S. subarctica population in England may be isolated and inbred.

Oilseed rape (Brassica napus) is a commercially important agricultural crop susceptible to damage from invertebrate herbivores, such as caterpillars, aphids and slugs. Plants can detect the presence of invertebrates via physical contact, tissue consumption, and on recognition of compounds in saliva. Plant retaliation includes the production of proteinase inhibitors to impair gut function and the accumulation of phenylpropanoids and potentially toxic glucosinolates to decrease plant palatability. Previous work has shown that a component of sunlight, ultraviolet-B (UV-B) radiation, can regulate defence related responses in a manner similar to that of pests and the plant wound-response hormone, Jasmonic acid (JA). The molecular basis behind UV-B- enhanced plant defence against invertebrates, however, remains elusive. This project aims to better understand invertebrate resistance in oilseed rape along with the genetic and metabolic basis of UV-B-enhanced defence against two agricultural pests, the grey field slug and caterpillars of the Diamondback moth (Plutella xylostella). UV-B treatment of B.napus and Arabidopsis thaliana has been found to enhance their resistance to these pests, and gene expression analysis of B.napus identified several genes similarly regulated by UV-B radiation, JA application, and/or slug or Plutella grazing. It is thought that these genes are important in UV-B enhanced plant resistance. Transgenic Arabidopsis lines over-expressing three of these oilseed rape genes have been generated to evaluate their role in UV-B-mediated defence. If found to be more resistant to pests, these lines will serve as ‘proof of concept’ that manipulation of the UV-B response pathway in members of the Brassica family could be used to develop new invertebrate resistant varieties.

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