| Summary: | This project aimed to provide a greater understanding about resistance to Pyrenopeziza brassicae in oilseed rape. A doubled haploid population of Brassica napus derived from a cross between the resistant oilseed rape cultivar Imola and a susceptible breeding line was used to map a single major locus associated with resistance to P. brassicae. The locus was positioned at the end of the linkage group corresponding to chromosome A1, a region homeologous to Arabidopsis thaliana chromosome 3. The resistance was associated with a phenotype that involved reduced P. brassicae subcuticular hyphal growth, the collapse of epidermal cells and an absence of asexual sporulation. P. brassicae was, however, able to sporulate sexually on senescent leaf tissue of the resistant plants. For the doubled haploid population, there were significant correlations between severity of light leaf spot assessed on field plots in Hertfordshire and Scotland and severity assessed on seedlings in controlled environment conditions. Analysis using quantitative peR showed that the lines of the doubled haploid population differed in their ability to support the growth of P. brassicae in controlled environment (on cotyledons and young leaves) and field conditions. The resistance present in oil seed rape cultivar Imola is different from that observed in other B. napus cultivars/lines, where asexual sporulation was observed on even the least susceptible cultivars/lines, and currently appears stable in different parts of the UK. An improved understanding of resistance to P. brassicae in B. napus will help to inform decisions about the deployment of new resistant cultivars to maximise the durability of the resistance.
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