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POSTERS: New and emerging diseases

Pectolytic bacteria associated with bacterial stem canker disease of hop (Humulus lupulus L.)
Michele Wiseman - Oregon State University. Megan Twomey- Oregon State University, Department of Botany and Plant Pathology, David Gent- USDA ARS, Briana Claassen- Oregon State University, Melodie Putnam- Oregon State University, Steve Massie- Washington Hop Commision, Maryna Serdani- Oregon State

In late summer fall of 2014, nearly all hop (Humulus lupulus L.) plants in a newly established yard of cultivar ‘Cashmere’ in Idaho suddenly wilted just prior to harvest. Affected plants had dark brown, occasionally water-soaked, cracked cankers often exuding a cream-colored ooze near the base of the plant. Exudate from the bleeding cankers had a distinctive odor that attracted numerous insects. Since then, the problem has been observed regularly on cultivar Cashmere in multiple regions of the U.S. Isolations from the margins of symptomatic material have consistently yielded an Enterobacter and Brenneria sp., but have also yielded a Corynebacterium sp., several species of yeast fungi, and a Pseudomonas sp. Attempts to reproduce symptoms with the recovered organisms have largely been unsuccessful unless plants are incubated at elevated temperatures (37-40°C). A multi-locus sequence analysis placed the most virulent isolates in a monophyletic clade with the known endophyte and plant pathogen, Enterobacter cloacae, and in a unique clade within the genus Brenneria, causal agent of drippy pod of lupine and bark canker diseases of several woody hosts. Research is underway to conclusively identify the causal organism, determine if these bacteria have additive detrimental effects as a disease complex, and elucidate the role of abiotic stress in disease expression on hop.