| Summary: | Parsnips (Pastinaca sativa) are a speciality crop, covering 3000 hectares across the UK, with a 93,000-tonne production and economic value of greater than £31M annually. Currently, the major constraints to production are losses associated with root canker disease, caused by a range of fungal pathogens. With no specific fungicides, development of long-term, sustainable resistance to parsnip canker is highly desirable. This work characterises the pathogens responsible, and develops tools to facilitate breeding for quantitative resistance to root canker diseases. Isolations and molecular characterisation of pathogens responsible for parsnip canker highlighted a range of fungal species, whilst canker symptoms were found to be clearly associated with certain pathogens. Cylindrocarpon destructans, Mycocentrospora acerina and to a lesser extent Itersonilia pastinacae were identified as the primary pathogens responsible for causing parsnip canker in the UK. Itersonilia spp. isolates from a range of hosts were found to infect parsnip roots and leaves, and produce both chlamydospores and ballistospores at a range of temperatures; furthermore, molecular characterisation failed to differentiate between species. For these reasons, Itersonilia should be described as a single species. For both C. destructans and M. acerina, isolates showed minimal variation in pathogenicity on parsnip roots and seedlings, and exhibited mycelial growth even at low temperatures. Phylogenetic analysis identified a species complex for both pathogens that could not be resolved by the ITS (Internal transcribed spacer) alone. Finally, parsnip root and seedling assays were developed to determine resistance to I. pastinacae, M. acerina and C. destructans within parsnip populations. QTL analysis of a parsnip genotyping population identified a significant QTL conferring resistance to M. acerina for use in a marker assisted breeding programme. The understanding of the pathology gained in this project will facilitate selection of resistant varieties, benefitting breeders, growers and through reduction in control mechanisms, society in general.
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