First report of Diaporthe humulicola causing halo blight of hop (Humulus lupulus L.) in Prince Edward Island, Canada

This study documents the first report of halo blight of hop (Humulus lupulus L.), caused by the fungal pathogen Diaporthe humulicola, in Prince Edward Island (PE), Canada. This pathogen has been previously reported in Michigan, New York, Connecticut and Quebec. Disease symptoms were reported in hopyards in Harrington and Mount Albion, PE. Symptoms reported include both foliar lesions and severe necrosis of hop cones. Through a metagenomic approach using Nanopore sequencing of the full Internal Transcribed Spacer (ITS) region products, multiple fungal species were identified in infected hop cones. Many plant pathogens were present in the hop cones including species of Botrytis, Alternaria, Colletotrichum and Fusarium. Additionally, metagenomic sequencing identified reads that most closely matched D. humulicola. Symptomatic leaf tissue sections were cultured on amended PDA to isolate the pathogen, then colony PCR was conducted and ITS regions were sequenced, confirming the identity of D. humulicola. Pathogenicity was validated using Koch's postulates on hop leaf disks, with lesion development occurring 7 days post-inoculation. Considering the humid conditions characteristic of eastern North American hop-growing zones, halo blight's emergence in PE emphasizes the need for comprehensive monitoring and improved best management strategies to protect the PE hop industry.