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POSTERS: New and emerging diseases

An emerging pathogen (Diaporthe sp.) of hop (Humulus lupulus) associated with foliar necrosis in commercial production yards in Michigan
Douglas S. Higgins - Michigan State University. Timothy Miles- Michigan State University, Mary Hausbeck- Michigan State University, Jan Byrne- Michigan State University

Hop (Humulus lupulus) production in the U.S. is expanding with 304 ha of hops harvested in Michigan (2018). In August 2018, two Michigan commercial hopyards reported a high incidence of necrotic leaf lesions with concentric circles on ‘Chinook’, ‘Centennial’, and ‘Crystal’. Preliminary identification of the isolates recovered from lesion margins was based on pycnidia morphology and the ITS region. A BLASTn search of the ITS region indicated partial homology (96.6% pairwise identity) to Diaporthe nomurai (AB302238 or KC343154.1) for 15 out of 19 isolates recovered. Neighbor-joining trees were created for the ITS and TEF1 loci using a NCBI Popset and eight representative Diaporthe sp. isolates recovered from hop leaf tissue. All eight Diaporthesp. isolates from hop clustered together on the same branch for both loci. The closest relatives were D. nomurai (KC343154.1), D. scobina (KC343195.1), and D. paranesis (KC343171.1) but based on these two markers the specific species could not be resolved. To test pathogenicity a detached leaf assay was performed. Ten-days post inoculation, irregular necrotic lesions with light brown pycnidia developed on all inoculated abaxial leaf surfaces. Multi-locus sequence typing is underway to determine the species identity. This work serves as a basis for future studies of the management of this emerging hop pathogen.