Suppression of Cucumber Green Mottle Mosaic Virus-Induced Disease by Organic Agricultural Materials in Watermelon

Abstract

Cucumber green mottle mosaic virus (CGMMV) causes mosaic, stunting, and fruit quality loss in watermelon, and no curative treatment exists once plants are infected. Six organic agricultural materials registered in Korea for viral disease control (A–F; three plant extract-based, two microbial extract-based, and one Serratia marcescens culture-based) were compared to mitigate CGMMV damage in watermelon. Transmission electron microscopy (TEM) revealed fragmentation of CGMMV particles after 12 hr of exposure to A, D, and F. In growth-chamber assays, all inoculated plants remained reverse transcription-polymerase chain reaction-positive, but C, D, and E reduced symptom incidence from 100% to 35–50%, and C, E, and F restored plant height to 30–33 cm versus 17 cm in untreated infected plants. CGMMV RNA accumulation was significantly reduced (by approximately 80% compared to the control by C, D, and E), ELISA absorbance did not differ significantly, and WRKY70 induction was material-specific (early induction by A and D). Combining D and E, selected for complementary profiles, gave the most consistent response: plant height 1.5-fold that of the infected control, 56.3% symptom incidence, and 2.8-fold WRKY70 expression, without a proportional decrease in virus accumulation; adding F provided no further benefit. In the field, C and E lowered infection incidence (54.2% and 58.3% vs. 91.7%) and disease severity index (47.0% and 39.2% vs. 87.5%), with reduced ELISA values. Thus, these materials act mainly by alleviating symptoms and growth suppression rather than by suppressing virus accumulation, supporting their response-based selection and combination as a complementary strategy against CGMMV in watermelon.