Dynamics of ascospore production in late autumn to develop better apple scab management strategies

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It is commonly assumed that the annual cycle of sexual reproduction of the apple scab fungus takes place on fallen leaves in the winter, producing ascospores as primary inoculum for the next spring. Furthermore, random mating among scab strains of opposite mating types is assumed. However, we recently showed that this random mating assumption is not supported by the data collected in a mixed orchard over the last ten years. Our data suggested that sexual mating is more likely to take place and succeed between isolates from lesions on the same leaf than contact between independently infected leaves in leaf litter on the orchard floor. Furthermore, our results also suggest that sexual reproduction is likely to be initiated before leaf-fall. If these are true, we need to re-visit current consensus/assumptions of scab population genetics, particularly regarding the recombination of existing fungal virulence factors, practicality of using mixed orchards, and management measures to reduce sexual reproduction before leaf-fall. This proposal will obtain direct evidence to answer Whether sex is initiated before leaf-fall;whether sex is more likely to succeed between lesions on the same leaves.Then, we will develop and evaluate (mostly microbial-based methods) control measures to disrupt sexual reproduction. Finally, we shall use the unique collection of scab indicator genotypes (as part of the global scab virulence monitoring programme) at NIAB EMR to demonstrate that recombination of scab virulence factors is unlikely. The results will have huge impact on predicting durability of resistance genes, feasibility of using mixed orchards, and reducing primary inoculum.