Characterisation and Distribution of Karaka Ōkahu Purepure Virus-A Novel Emaravirus Likely to Be Endemic to New Zealand

Abstract

We report the first emaravirus on an endemic plant of Aotearoa New Zealand that is, to the best of our knowledge, the country's first endemic virus characterised associated with an indigenous plant. The new-to-science virus was identified in the endemic karaka tree (Corynocarpus laevigatus), and is associated with chlorotic leaf spots, and possible feeding sites of the monophagous endemic karaka gall mite. Of the five negative-sense RNA genomic segments that were fully sequenced, four (RNA 1-4) had similarity to other emaraviruses while RNA 5 had no similarity with other viral proteins. A detection assay developed to amplify any of the five RNAs in a single assay was used to determine the distribution of the virus. The virus is widespread in the Auckland area, particularly in mature trees at Ōkahu Bay, with only occasional reports elsewhere in the North Island. Phylogenetic analysis revealed that its closest relatives are pear chlorotic leaf spot-associated virus and chrysanthemum mosaic-associated virus, which form a unique clade within the genus Emaravirus. Based on the genome structure, we propose this virus to be part of the family Emaravirus, but with less than 50% amino acid similarity to the closest relatives in the most conserved RNA 1, it clearly is a novel species. In consultation with mana whenua (indigenous Māori authority over a territory and its associated treasures), we propose the name Karaka Ōkahu purepure virus in te reo Māori (the Māori language) to reflect the tree from which it was isolated (karaka), a place where the virus is prevalent (Ōkahu), and the spotted symptom (purepure, pronounced pooray pooray) that this endemic virus appears to cause.