Invasive Species Compendium

Detailed coverage of invasive species threatening livelihoods and the environment worldwide

Abstract

First report of apple hammerhead viroid in the United States, Japan, Italy, Spain, and New Zealand.

Abstract

In June of 2017, a 'Honeycrisp' apple (Malus pumila) cultivar from central Washington (USA) exhibiting shoot decline and dieback symptoms was submitted for diagnosis to the Washington State University Clean Plant Centre Northwest. Total RNA was extracted from blade, midrib and petiole tissue of leaves removed from the symptomatic plant. Sequence data analysis showed that the plant was infected with Apple stem grooving virus, Apple stem pitting virus, Apple chlorotic leaf spot virus, Apple green crinkle-associated virus, and Apple hammerhead viroid (AHVd), a circular RNA containing hammerhead ribozymes first identified in China and recently shown to be a bona fide viroid. AHVd presence was confirmed by one-step reverse transcription polymerase chain reaction. High-throughput sequencing data were available for 8 of the 10 positive samples and confirmed AHVd presence in an additional sample from Washington, one from Ohio (USA), one sample each from Japan and New Zealand, and two samples each from Italy and Spain. Although AHVd has been detected in apple trees with trunk splitting and shoot decline and dieback (this study), none of the other apples surveyed in this study or others exhibited disease symptoms. This is thought to be the first report of AHVd in the USA, Japan, Italy, Spain and New Zealand.