Responses of wheat to infection by Mycosphaerella graminicola

The necrotrophic fungal pathogen Mycosphaerella graminicola causes septoria tritici blotch, the most important foliar disease of wheat in Europe. During a compatible interaction, host responses to infection allow the development of necrosis as a form of programmed cell death which appears to aid infection rather than hindering it. Aspects of the response of wheat to infection with M. graminicola were studied. \nBlumeria graminis f. sp. tritici causes powdery mildew disease of wheat. A method for dual inoculation of wheat with both M. graminicola and mildew was developed. Leaves preinoculated with virulent M. graminicola and subsequently inoculated with a normally virulent isolate of B.graminis had substantially reduced formation of mildew colonies, conidiophores and conidia. This was not the result of reduced success of infection or early development of B. graminis spores on leaves inoculated with virulent M. graminicola. \nExpression of 11 plant defence- and senescence-related genes was tested in eight variety/isolate combinations which involved Stb6 and Stb15, the two most common resistance genes in European wheat. Inoculation with M. graminicola caused a large effect on plant gene expression with seven genes showing differential expression compared to mock inoculated controls. Patterns of gene expression were largely characteristic of varieties rather than compatible or incompatible interactions in general. TaMPK3 protein accumulated in all the compatible interactions tested, above the level of the mock-inoculated controls, but also accumulated in some incompatible interactions, although not to greater levels than the mock-inoculated controls, implying that this is a consistent feature of the wheat M. graminicola-wheat interaction. \nThree common microscopy stains were tested to develop a reliable method of investigating M. graminicola growth and development during wheat infection, especially visualisation in the apoplast. None of the stains tested were suitable for this purpose, implying that the fungal hyphal wall is modified or protected within the plant