Understanding the transmissibility of cucumber green mottle mosaic virus in watermelon seeds and seed health assays

Authors: SUI, XUELIAN - Fujian Agricultural & Forestry University; Li, Rugang; Shamimuzzaman, Md - Shamim; WU, ZUJIAN - Fujian Agricultural & Forestry University; Ling, Kai-Shu

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/19/2018
Publication Date: 12/27/2018
Citation: Sui, X., Li, R., Shamimuzzaman, M., Wu, Z., Ling, K. 2018. Understanding the transmissibility of cucumber green mottle mosaic virus in watermelon seeds and seed health assays. Plant Disease. https://doi.org/10.1094/pdis-10-18-1787-re.
DOI: https://doi.org/10.1094/pdis-10-18-1787-re

Interpretive Summary: Cucumber green mottle mosaic virus (CGMMV) in genus Tobamovirus, family Virgaviridae, first described in 1935 infecting cucumber in England, has become a major re-emerging viral pathogen that cause serious yield losses to a number of cucurbit crops worldwide, including the U.S. These global outbreaks of CGMMV have caused serious concerns to cucurbit industries and vegetable seed companies. The accelerated geographical expansion and greater severity from the disease outbreaks of CGMMV in various cucurbit crops are likely due to the nature of seed transmission of the virus in contaminated commercial seed lots through ever increasing activities of off-shore hybrid seed production, global seed trade, and intensive cucurbit production. In this study, in collaboration with a visiting scholar from China, ARS scientists in Charleston, SC conducted experiments to determine the ease of mechanical transmission of CGMMV from contaminated seed to seedlings, evaluate various molecular and serological methods for seed health tests, and need for a bioassay to achieve an accurate risk assessment. An effective and efficient seed health assay program would require a sensitive lab test and an efficient bioassay to make meaningful risk assessment.

Technical Abstract: Cucumber green mottle mosaic virus (CGMMV), an emerging tobamovirus, has caused serious disease outbreaks to cucurbit crops in a number of countries around the world. The worldwide emergence of this viral disease is likely resulting from increasing global seed trade of potentially CGMMV-contaminated cucurbit seeds. Although CGMMV is seed-borne, the mechanism of its transmission from a contaminated seed to germinating seedling is still not fully understood. To evaluate the mechanism of seed transmissibility, using highly contaminated watermelon seeds extracted from CGMMV-infected experimental plants in a containment greenhouse, we did not observe true seed transmission of CGMMV to germinating seedlings through natural seedling grow-out. However, efficient transmission of CGMMV was observed using bioassays on melon plants through mechanical inoculation of seed extract prepared from CGMMV-contaminated seeds. Understanding the seed-borne and ease of mechanical transmission of CGMMV from a contaminated seed to seedling is an important foundation to employ not only an effective seed health test to ensure virus-free status, but also a meaningful bioassay to determine the virus viability detected on a contaminated seed lot. To achieve this goal, we conducted comparative evaluation of molecular (Real-time PCR and LAMP) and serological techniques (ELISA and lateral flow device) for their usefulness in seed health tests. CGMMV is seed-borne and a highly contagious virus. With increasing activities in the off-shore seed production and ever expanding global seed trade of cucurbit seeds, an effective and efficient seed health assay program would require a sensitive lab test and an efficient bioassay to make meaningful risk assessment.