Improved management options for Cucumber green mottle mosaic virus

Abstract

The first Australian detection of Cucumber green mottle mosaic virus (CGMMV) was in the NT in September 2014, on commercial watermelon farms. It was subsequently detected in cucurbit varieties including cucumber, pumpkin, squash and Asian cucurbit vegetables. After the NT detection, CGMMV was also found in isolated areas of Queensland, South Australia, cucurbit-growing areas of Western Australia and, more recently, New South Wales. Studies were conducted to help manage the disease, specifically investigating alternative hosts and non-hosts, studying CGMMV biology in contaminated soil, improving diagnostics for plant and seed detection and investigating the role of honey bees in CGMMV spread. Six alternative crops were identified as non-hosts of CGMMV from field and pot trials in the NT – sweet corn, snake bean, capsicum, okra, sorghum and peanut. Eight weed species were shown to be alternative hosts and some weed seeds also tested positive for CGMMV. Soil spiked with sap from CGMMV-contaminated plants remained infectious for up to 36 weeks; direct sowing of seeds into contaminated soil resulted in less infection than transplants, due to damaged root systems of transplants permitting virus entry. Molecular testing of cucurbit seeds showed that a broad range of cucurbit species can be tested, requiring sub-samples of up to 500 seeds for most species. A new lateral flow dipstick was developed and preliminary results showed it was able to detect the outbreak strain of CGMMV at a 1:103 dilution. A bee sampling protocol was developed, and bee products found to harbour CGMMV included bees, brood, pollen, honey, wax and propolis. Viable CGMMV was only found in adult bees, pollen and honey. A new project will investigate modes of transmission of CGMMV by honey bees. Future research should further investigate efficacy of disinfectants for new seedlings, the role of alternative hosts in CGMMV epidemiology and resistant/tolerant cucurbit varieties.