Moderate UV-A supplementation benefits tomato seed and seedling invigoration: a contribution to the use of UV in seed technology

The production, processing and consumption of Solarium lycopersicum L. fruits are increasing worldwide, demanding technologies to improve tomato growth efficiency. Germination is a critical step for intensification of crop production and conditions plants' vigor, a crucial benchmark in plant market. Ultraviolet radiation supplementation is emerging in seed technology as it increases plant growth with no impact on the environment, although its use in crops' nurseries still remains an open field. In the present work, seeds/seedlings of three commercial cultivars ('Oxheart', 'Cherry' and 'Roma') were grown for 15 days under three different ultraviolet (UV)-conditions. The results demonstrated the benefits of supplementing seeds/seedlings with moderate UV-A dose, being evident an acceleration/synchronization of germination rates, higher biomass and cotyledon area, and a stimulation of photosynthetic pigments and anthocyanins in all cultivars analysed. UV-B showed a cultivar dependence effect: 'Cherry' cultivar was in general not affected by the moderate UV-B dose used, but 'Roma' and 'Oxheart' showed a delay in germination and a seedling biomass decrease, in parallel with a decrease in chlorophylls and carotenoids. Both UV-AB supplements reduced the H2O2 and MDA seedling levels, but the antioxidant battery was stimulated (e.g., peroxidases that use guaiacol as a substrate (GPX)) as well as the phenol level and the antiradical activity. The Principal Component Analysis (PCA) validates the clear distinction between cultivars and UV-condition effects. These data demonstrate the benefits of UV-A supplementation of tomato seeds pointing out to an eustress beneficial of UV-A in seedlings growth and vigor. A possible application of UV-A supplementation to other crops is discussed.