Innovative control of the cucurbit powdery mildew: Combining nanoencapsulated dsRNA and low-dose fungicides for sustainable crop protection.

The rise of fungicide-resistant pathogens and increasingly strict regulatory frameworks have heightened the demand for sustainable alternatives in plant disease control. This study assesses the potential of spray-induced gene silencing (SIGS) targeting SdhC, a critical subunit of the mitochondrial succinate dehydrogenase (SDH) complex and determinant of SDHI fungicide resistance, for managing Podosphaera xanthii, the causal agent of cucurbit powdery mildew. To evaluate this approach, PxSdhC double-stranded RNA (dsRNA) was initially infiltrated into melon cotyledons, resulting in a 65% reduction in fungal biomass and a 60% decrease in SdhC gene expression, validating its effectiveness for SIGS applications. A key achievement of this study was the demonstration that strong disease control can be achieved with substantially reduced doses of SDHI fungicides when combined with PxSdhC-dsRNA, providing the first direct evidence of the synergistic potential of this strategy. Building on these results, greenhouse trials were conducted in which dsRNA was applied in both naked and carbon dot (CD)-nanoencapsulated forms, alone or in combination with low doses of the SDHI fungicides boscalid and fluopyram. Nanoencapsulation enhanced dsRNA stability and extended gene silencing effects, achieving up to 69% and 53% disease suppression at 14- and 21-days post-inoculation, respectively. Moreover, combined treatments with PxSdhC-dsRNA-CD and low-dose fungicides exhibited synergistic effects, with disease suppression ranging from 33% to 91%, depending on isolate resistance levels. Sensitive and low-resistance isolates responded effectively, while efficacy declined in highly resistant ones. In vitro specificity assays confirmed that PxSdhC-dsRNA selectively inhibited Botrytis cinerea, a species with high SdhC sequence homology, without affecting unrelated fungi. Altogether, these results highlight the promise of gene-targeted, nanoformulated dsRNA as an effective, precise, and environmentally friendly strategy for integrated disease management, capable of boosting the performance of low-dose fungicide applications and reducing chemical input.