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Two emerging pathogens associated with rapid decline and dieback symptoms in apple detected in Washington, USA

Stephanie Szostek: Washington State University

<div>Material from Honeycrisp apples exhibiting rapid decline and dieback symptoms in Washington state was submitted to the WSU Clean Plant Center Northwest (CPCNW) for diagnosis. Using high-throughput sequencing (HTS), these plants were found to contain <em>Apple stem grooving virus</em>, <em>Apple stem pitting virus</em>, <em>Apple chlorotic leafspot virus</em>, and <em>Apple green crinkle-associated virus</em>, all well established in the United States, as well as Apple hammerhead viroid (AHVd) and Citrus concave gum-associated virus (CCGaV). The presence of AHVd and CCGaV in these samples was verified by RT-PCR and represents the first report of these two pathogens in the U.S., and the first report of CCGaV in apple. A selection of apple material submitted to the CPCNW for diagnostic and virus elimination procedures was then screened by HTS and RT-PCR for AHVd and/or CCGaV. AHVd was detected by both methods in material originating from Washington and Ohio, USA, Japan and Italy. Both methods detected CCGaV in apple plants from Washington and Oregon, USA, and Australia, France, Italy, and Spain. Decline and dieback symptoms were only observed in Honeycrisp infected with AHVd and CCGaV; the presence of the other viruses did not produce symptoms in neighboring trees suggesting that one or both of these are responsible for the disease observed. Given that AHVd is known to produce trunk swelling and splitting in Gala apple, both pathogens are significant and emerging diseases of apple production worldwide.</div>