Effect of UVB radiation on two types of lettuce crop in hydroponic system

Leafy vegetable consumption has increased in recent years due the relation between fresh product consumption and good health. Today consumers demand fresh vegetables with health benefits associated with functional compounds as phenolic compounds. So, there is a bigger interest in different types of coloured leafy vegetables such as lettuces. It is known that the functional value of leafy vegetable is affected by internal and external factors during culture. Among external factors UVB radiation can generate important morphological and phytochemical changes in plants. If the plant is exposed to high UVB doses this can generate leaf damage by the accumulation of ROS, but if controlled doses are used, phenolic compounds synthesis in the plant may be activated. Consumers also have an especial preference for hydroponic leafy vegetables due to their visual quality; however, UVB radiation is excluded when the culture is carried out under plastic greenhouse. The purpose of this study was to compare the responses of hydroponic Lollo Bionda 'Levistro' and Lollo Rosso 'Carmoli' lettuces cultivated under different UVB doses to increase phenolic compounds content in leaves. For this, three continuous harvests were performed to evaluate the evolution phenolic compounds content. Before the first harvest, lettuces were treated with 0, 5.2 and 10.5 kJ m(-2) of accumulated UVB radiation dose. After that, lettuces were not treated to identify if there is a radiation memory. Finally, after second harvest, the same UVB treatments were applied again. The highest UVB doses generated visual damage on Lollo Bionda 'Levistro' and Lollo Rosso 'Carmoli' lettuces. Only 'Levistro' yield was affected by UVB at third harvest and no TPC effect by UVB radiation was registered in any cultivar. Despite the above, the highest UVB treatment increased total flavonoids in both cultivars at third harvest.