UV-B radiation causes early ripening and reduction in size of fruits in two lines of tomato (Lycopersicon esculentum Mill.)

An open-air experiment was performed in Pistoia (Italy) to investigate the possible protective role played by different contents of W-B absorbing comp ounds to realistic UV-B supplementation and to study its effect on plant fr uit production. A mutant line and its normal counterpart of Lycopersicon es culentum Mill, which differ in the content of UV-B absorbing compounds, wer e used. Additional UV-B radiation in the field was supplied to simulate a 2 0% stratospheric ozone depletion. Two groups of plants were grown:'control' , where plants received only natural solar UV-B radiation, and 'UV-B' treat ment, where plants were grown under supplemental UV-B. The results of the experiment showed that the content of UV-B absorbing com pounds of treated plants did not differ from that of the control in both li nes. This indicates that natural sunlight, in Mediterranean areas, is satur ating for synthesis of these compounds also in plants with normal content o f UV-B absorbing compounds. Consequently, plants are not able to produce si gnificant additional amounts of them, in response to a realistic UV-B suppl ementation, in order to protect the plant from additional UV-B radiation. No different responses to the UV-B supplementation were found between the t wo lines. The most significant UV-B effect was an earlier reddening of frui ts in comparison with the 'control' accompanied by a reduction in the size of mature fruits. No significant effects of UV-B treatment were observed in biomass accumulation, leaf ontogeny, flowering or productivity.