Synergistic Effects of UV-B and UV-C in Suppressing Sclerotinia sclerotiorum Infection in Tomato Plants

Ultraviolet radiation has emerged as an eco-friendly biocontrol agent. However, since high doses of UV are biocidal, it is crucial to determine the effects and optimal doses of UV both for fungal pathogens and host plants to maximise the benefits of such treatments. This study investigated the effects of UV-B, UV-C, and their combination treatments on Sclerotinia sclerotiorum, a major fungal pathogen, and tomato plants infected with S. sclerotiorum. Our results showed that the optimised cumulative UV dosage suppressed in vitro sclerotia germination, inhibited mycelial growth, increased reactive oxygen species and lipid peroxidation accumulation and suppressed superoxide dismutase activity in plants. In S. sclerotiorum-inoculated tomato plants, combining UV-B (3600 J/m(2)) and UV-C (930 J/m(2)) or applying UV-C (930 J/m(2)) alone was more effective in suppressing the pathogen (81%) compared to the UV-B (3600 J/m(2)) alone. The combination treatment also significantly improved fruit number per plant (1.83-11.88-fold), biomass (2.03-3.46-fold), bioactive compound contents (total phenolic content (1.28-6.03-fold), total flavonoid content (1.29-5.39-fold), and ascorbic acid (1.30-7.70-fold)). Additionally, the expression of defence genes (PR1, PR2, PR5, PDF1.2, VSP2, PR3, and PR 4) in combination treatment was significantly higher than in non-treated plants and individual UV-B or UV-C treatments. This is the first report demonstrating the synergistic effect of UV-B and UV-C as an effective tool for suppressing plant disease, enhancing yield, and improving the quality of agricultural produce, suggesting its potential as a combinatorial treatment for suppressing fungal diseases in crop plants.