CHARACTERIZATION OF MITE-ASSOCIATED VIRUSES IN PLANT PATHOSYSTEMS OF HAWAII

Abstract

Although mites' ability to vector plant viruses was demonstrated long ago, there remains a significant knowledge gap for these viruses and their interactions with their plant host and mite vector compared to other arthropod-vectored plant viruses. Most mite-transmitted plant viruses are vectored by mites that belong to the superfamily Eriophyoidea and the genus Brevipalpus (Acari: Tenuipalpidae). Viruses transmitted by eriophyid mites belong to at least seven genera, but Emaravirus members (family Fimoviridae) are considered emergent plant viruses of agricultural importance. The viruses transmitted by brevipalpus mites, also known as Brevipalpus-transmitted viruses (BTVs), belong to three genera classified within two families, Dichorhavirus (family Rhabdoviridae) and Cilevirus and Higrevirus (family Kitaviridae). The goal of this study is to lessen the knowledge gap for this group of plant viruses by further characterizing the genomics and biology of new and existing mite-associated viruses. In this work, we identify passionfruit (Passiflora edulis) as a new host for the BTV citrus leprosis virus C2 (genus Cilevirus). Also, after more than 60 years of absence, we report citrus leprosis in the US and determined it is caused by an orchid strain of the BTV orchid fleck virus (genus Dichorhavirus). This discovery has led to an eradication effort for this federally-actionable pest. A new BTV, named hibiscus yellow blotch virus (HYBV), was characterized, and provisionally placed within the genus Cilevirus. HYBV represents an evolutionary lineage between cileviruses and higrevirus and was detected in Brevipalpus yothersi, representing this new virus's potential vector. New hibiscus and citrus isolates of hibiscus green spot virus 2 (HGSV-2; genus Higrevirus) were characterized and found to possess low genetic diversity. The foundation for a reverse genetics system for BTVs was established through the development of an infectious clone of HGSV-2 that was capable of establishing infection in several natural and experimental plant hosts. This represents the first infectious clone developed for a BTV and a critical tool for future research in this arena. Finally, the transmission of HGSV-2 was demonstrated using B. azores mites. This is the first report of B. azores, having the capability to transmit viruses, and confirms HGSV-2’s status as a BTV. The virome of populations of flat mites collected from several plant hosts from two Hawaiian Islands was found to be predominated by picornavirids. Kita and Kita-like viruses were also found and supported a possible evolutionary scenario in which kitavirids emerged from arthropod-specific viruses such as negeviruses. A partial sequence of a putative new cile-like virus was found in tenuipalpid mites collected from pineapple. This virome study warrants further examination of flat mite populations from different hosts and geographic origins to surveil for and understand the diversity of BTV and BTV-like agents. Finally, ti ringspot-associated virus (TiRSaV) was characterized and found to contain at least five genomic segments, which could be detected in symptomatic ti plants (Cordyline fruticosa) only. TiRSaV was also detected in two putatively novel species of eriophyid mites recovered from symptomatic plants.