An asymptomatic watermelon mosaic virus variant confers drought tolerance in cucumber plants

• Watermelon mosaic virus delays drought symptom development in cucumber • Virus-infected plants retain higher water content under drought conditions • WMV reduces ABA but enhances SA, JA, and osmoprotective metabolite levels • Proline accumulation is amplified under combined virus and drought stress • Viral-induced drought tolerance is uncoupled from cucumber fruit yield Plant viruses may enhance host tolerance to drought. Here, we used an asymptomatic strain of watermelon mosaic virus (WMV-strain Vera) in cucurbits to evaluate drought tolerance in Cucumis sativus cv. Supermarketer. Plants were inoculated with WMV and subjected to water withholding. The development of drought symptoms in WMV-infected plants was compared to mock-inoculated controls. WMV-infected plants consistently showed delayed drought symptom onset. Viral genome accumulation revealed an increased rate under drought stress. Water content analysis revealed that infected plants maintained significantly higher water content per unit mass compared to controls. Interestingly, drought tolerance was not directly associated with stomatal closure. Hormone and metabolite profiling showed substantial changes. Abscisic acid (ABA), typically associated with drought response, decreased significantly in infected plants under drought stress. Conversely, salicylic acid (SA) and jasmonic acid (JA), hormones linked to biotic stress tolerance, accumulated to higher levels in infected plants before and after stress. Several metabolites associated with osmoprotection and antioxidant activity were also present at higher concentrations in WMV-infected plants, including compounds that support osmotic adjustment, membrane stabilization, and protection of proteins and cellular machinery from oxidative damage. Proline content increased under both drought and viral infection, with an additive effect in WMV-infected plants exposed to drought. Despite enhanced stress tolerance, no correlation was found between virus-induced drought tolerance and fruit yield parameters, including fruit weight, size, quantity, or seed number. Overall, WMV infection promotes drought tolerance in cucumber independently of transpiration, through modulation of hormone signaling and accumulation of protective metabolites.