The role of endophytes in affecting symptom development of European apple canker caused by Neonectria ditissima

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European Canker, caused by Neonectria ditissima, has become the most damaging disease of apple in recent years across all major apple growing regions worldwide. Modern cultivars lack resistance to this pathogen and in Europe most effective methods of chemical control are no longer available. Cultivars differ in their susceptibility but there is no absolute resistance. We obtained preliminary data that indicate a possible link of antagonist fungal endophytes with cultivar tolerance to N. ditissima. The most damaging aspect of the disease is from latent infections in nurseries that become active and develop into canker on the main trunk soon after planting in orchards - leading to tree death. Ample empirical evidence suggests that stresses following planting can promote symptom expression of those nursery-origin latent infections. In this proposal, we aim to investigate whether cultivar differences in tolerance to N. ditissima are associated with specific endophytes and, if so, identify the organism(s) for further biocontrol assay. Expression of specific genes in the SA and JA pathways will be assayed following inoculation of candidate endophytes to ascertain whether endophytes induce host defence responses that may contribute to canker suppression. Next, we will use a mapping population from a cross between canker resistant and susceptible cultivars to map QTLs that are responsible for recruiting specific endophytes and to determine the extent of overlapping of these QTLs with those mapped for canker resistance. Then, we shall study the extent to which endophyte profiles of a specific genotype are affected by individual or combined soil water deficit, AMF and PGPR treatments. Finally, we shall conduct a common garden experiment to assess (1) to what extent recruitment of endophyte profiles is influenced by soil characteristics, soil microbiota, and host genotypes, and (2) whether canker development is influenced by specific endophytes and plant defence signalling in response to biotic and abiotic factors (represented by different sites). Plant hormone response is measured in terms of specific hormones - JA, SA and ABA; endophyte composition will be characterised by next generation sequencing technology. The output of this work will not only lead to a deeper understanding of the biology and epidemiology of the disease, but also develop tools and knowledge for practical disease management, which can be efficiently adopted by the industry due to their active involvement in the project.The industry is supporting this proposal through the LINK scheme, as they recognise the need for a comprehensive strategy to manage the canker disease. Six industry partners will provide both cash and in-kind contribution to this proposal.