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Potential role of soil and plant microbial communities in rapid and sudden decline of established apple trees

Katchen Julliany Silva: Cornell University

<div>Rapid decline of established apple trees across Central and Northeastern regions of the United States, and in Ontario, Canada has been more frequently reported in recent years. Typical characteristics of sudden or rapid apple decline (RAD) syndrome are chlorotic leaves throughout the entire canopy followed by tree collapse within weeks. Possible causes include abiotic and biotic stresses, viruses, rootstock and scion compatibility, and their interactions. However, the potential role of soil and endophytes in RAD has not been studied to date. Next-generation sequencing has shown tremendous opportunity for studying phytopathogen composition and their association with plant diseases. We are analyzing the diversity of bacterial and fungal communities in the soil and rhizosphere, as well as endophytes within the rootstock and scion of both declining and healthy looking apple trees from affected orchards at sequence level to narrow down potential causes of RAD. We are using high-throughput 16S rRNA and ITS1/ITS4 rRNA amplicon sequencing, targeting V3-V4 and ITS1-ITS4 regions, respectively, of Honeycrisp cultivar grafted on M9 rootstock. A comprehensive list of endophytic microorganisms that might play a crucial role (directly or indirectly) in RAD has been developed. A more narrowly focused selection will be used for in-depth analysis. The future direction of research to further understand plant–microbe interactions and their role in RAD will also be presented.</div>