Occurrence of cucumber green mottle mosaic virus in Western Australia

In 2014, cucumber green mottle mosaic virus (CGMMV) was detected for the first time in Australia infecting watermelon crops in the Northern Territory (NT). In July 2016, a leaf sample was collected from a cucumber plant with leaf mottle and distortion symptoms growing in a commercial plastic tunnel house at Geraldton, Western Australia (WA). Testing by multiple methods confirmed CGMMV presence in the cucumber sample. Delimiting surveys of five of the main cucurbit growing areas in WA were conducted to determine the extent of CGMMV occurrence. This survey included commercial cucurbit farms (field and protected cropping), roadside verges (primarily Cucurbitaceae weeds) and seedling nurseries. A total of 22,905 leaf samples from cucurbit crop plants or weeds were collected and tested for CGMMV. Out of the 95 locations surveyed, 16 locations in the Kununurra, Carnarvon, Geraldton or Perth cropping regions were found to have plants infected with CGMMV. CGMMV was detected in cucumber, rockmelon, honeydew melon and watermelon crops in the open field or protected cropping facilities, and in the native plant Cucumis myriocarpus and naturalized weed Cucumis variabilis. Seven whole genome sequences of CGMMV were obtained using high throughput sequencing (HTS), with 99.1–99.9% nucleotide identities to each other. Phylogenetic analysis showed that the 7 new sequences grouped with 2 other Australian sequences, two from the USA and one from the Netherlands. This highlights the limited genetic diversity of CGMMV within Australia suggesting a single recent incursion.