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

由白僵菌引起的欧洲溃烂病近年来已成为苹果危害最大的病害，遍及全球所有主要苹果产区。现代品种缺乏对这种病原菌的抗性，在欧洲，不再有最有效的化学防治方法。不同品种感病能力不同，但不存在绝对抗性。我们获得的初步数据表明，拮抗真菌内生菌可能与栽培品种对白粉病的耐性有关。这种疾病最具破坏性的方面是苗圃的潜伏感染，在果园种植后不久，这些感染变得活跃，并在主干上发展为溃烂-导致树木死亡。大量的经验证据表明，种植后的压力可以促进这些苗圃来源的潜伏感染的症状表现。在这项建议中，我们的目标是调查品种对白粉病的耐受性差异是否与特定的内生真菌有关，如果是的话，则确定该生物(S)以进行进一步的生防试验。在接种候选内生菌后，将分析SA和JA途径中特定基因的表达，以确定内生菌是否诱导可能有助于抑制溃烂的宿主防御反应。接下来，我们将使用抗腐病和感病品种杂交的作图群体来定位负责招募特定内生菌的QTL，并确定这些QTL与那些定位的抗溃烂QTL的重叠程度。然后，我们将研究单独或联合土壤水分亏缺、AMF和PGPR处理对特定基因型的内生菌分布的影响程度。最后，我们将进行一个普通的花园实验，以评估(1)土壤特性、土壤微生物区系和寄主基因对内生菌分布的影响程度，以及(2)特定的内生菌和植物对生物和非生物因素(由不同地点代表)的防御信号是否影响溃烂的发展。植物激素反应是根据特定的激素-JA、SA和ABA来衡量的；内生菌的组成将通过下一代测序技术来表征。这项工作的成果不仅会加深对该病的生物学和流行病学的了解，还会为实际的疾病管理开发工具和知识，由于他们积极参与该项目，因此可以有效地被业界采用。业界通过联系计划支持这项建议，因为他们认识到需要一个全面的策略来管理溃烂疾病。六个行业合作伙伴将为这项提议提供现金和实物捐助。

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.