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A previously undiscovered Emaravirus associated with witches broom symptoms in blue palo verde (Parkinsonia florida) trees in Arizona

A. Sofia Avelar: School of Plant Sciences, University of Arizona

<div>Palo verde witches broom disease (PVWBD), of unknown etiology, affects blue palo verde (<em>Parkinsonia florida</em>) trees. Broom symptoms are manifested as dense clusters of shortened, thornless branches with stunted leaves. Recently, the disease has spread widely in Arizona nurseries and landscapes, causing irreversible damage and sometimes requiring tree removal. In this study, the suspected causal agent of PVWBD has been associated with symptomatic trees for the first time. During 2015-2016, leaves, flowers, and seeds were collected from symptomatic and asymptomatic blue palo verde trees. Total RNA was isolated and RNASeq libraries were sequenced using the Illumina Hi-Seq 2500 platform. Four RNA components of 7, 2, 1.4, and 1.5 kilobases were recovered, at 60-65% similarity (BLASTn) with <em>Wheat mosaic virus</em> (<em>Emaravirus</em>; <em>Fimoviridae</em>), a negative-sense, single-stranded RNA virus with an eriophyid mite vector. Reverse-transcriptase PCR amplification with primers specific for RNAs 1-4 and Sanger sequencing of the cloned amplicons confirmed the presence and absence of four RNA components in symptomatic and asymptomatic samples, respectively. The apparently complete viral genome, and presence of the mite <em>Aculus cercidii</em><em> </em>(Keifer) infesting palo verde trees, indicates the first association of a previously undescribed emaravirus with witches broom disease of palo verde. The virus name, <em>Palo verde witches broom virus </em>(PVWBV), is proposed.</div>