Detection of exotic biosecurity threat ribgrass mosaic virus and novel tobamoviruses through metatranscriptomic sequencing of animal gut content

Ribgrass mosaic virus (RMV) and related viruses of the genus Tobamovirus ( Virgaviridae ) are cruciferous plant pathogens that represent a threat to global horticultural systems. In Australia, they are considered exotic biosecurity threats, and an incursion of these viruses would require rapid and strict control efforts. However, current surveillance methods for these viruses are limited. We examined whether RMV and related tobamoviruses could be detected by deep sequencing of gut metatranscriptomes of vertebrate animals and ticks. Using this method, we discovered that RMV, as well as a novel relative of RMV, and two highly diverse novel tobamoviruses are present in Australia. RMV was detected in multiple sites in both the Australian Capital Territory (ACT) and Tasmania, two regions separated by approximately 700km of land and 200km of water. The novel relative of RMV was detected in the ACT and New South Wales (NSW), while the highly divergent novel tobamoviruses were each detected in a single state, NSW and Queensland (QLD). In addition, Tobacco mild green mosaic virus, which is already known to be present in Australia, was detected in QLD using this method. This work highlights the potential utility of metatranscriptomic sequencing of wild animal gut for the surveillance of biosecurity threats to native and agricultural plant species. Importance Plant viruses can have devastating impacts on global horticulture. Tobamoviruses (family Virgaviridae , genus Tobamovirus ) are among the most damaging seed-borne viruses in horticultural crops, and Australia is free of many of the tobamoviruses that cause major crop losses in other countries. These viruses are extremely difficult to eradicate. Consequently, early detection of incursions is key to the control of these viruses in Australia, alongside rapid deployment of eradication and management plans. Current biosecurity surveillance methods in Australia rely on visual inspection, immunological assays, and molecular methods such as screening of imported seed lots. This study introduces a complementary approach that utilises unbiased metatranscriptomic sequencing of animal gut material to detect cryptic plant viruses circulating in nature. Using this approach, we detected five different tobamovirus circulating in Australia, including a virus thought to be exotic and three novel viruses. This unique approach highlights alternative options for surveillance/detection of exotic crop viruses.