Timing of Antiviral Compounds (Quercetin, Acyclovir, and Chalcone) for the Management of Papaya Ringspot Virus in Zucchini (<i>Cucurbita pepo</i> L)

The use of antiviral compounds presents a promising strategy for managing plant viruses such as Papaya ringspot virus(PRSV), which infects zucchini and numerous other crops worldwide, leading to significant yield losses. This study aimed to evaluate the efficacy of three antiviral compounds-quercetin, acyclovir, and chalcone-against PRSV under greenhouse conditions. Treatments were applied at three concentrations (100, 200, and 500 ppm) and at two different time points post-inoculation (2 days and 9 days), representing early and late applications, respectively. The results revealed that, the early application; 2 days with the concentrations of 100 and 200~ppm reduced significantly PRSV disease severity compared to late application. For example, the disease severity percentages for early versus late treatments were as follows: quercetin (31.25 vs. 39.58%), chalcone (31.25 vs. 39.58%), and acyclovir (31.25 vs. 40.62%). Moreover, the early treatments resulted in statistically significant increases in plant height, fresh and dry biomass, as well as total chlorophyll and carbohydrate concentrations in zucchini plants, relative to the untreated control. These results suggest that the tested antiviral compounds represent an effective, environmentally friendly approach to managing PRSV, supporting sustainable agricultural practices and reducing dependence on synthetic pesticides.