Proline test to evaluate light stress in tomato seedlings under artificial light

Light is one of the most bounding environmental factors for vegetable growth, being also important for young plants development. For this reason nurseries often make big investments in cultivation chambers where artificial lighting is used to obtain high quality plants, as supported by a survey realized to the nurseries of Almería (Spain). Nevertheless, seedling response is modified by intensity and quality of spectrum light; also the radiation threshold that generates stress must be considered. This work presents the stress response of fifteen tomato cultivars seedlings under different lights, based on leaves proline concentration, to evaluate the interest of the application of complementary light in nursery production system. Compact (low energy-consuming), high-efficiency and standard fluorescent lamps were used. The trial was carried out in a growth chamber with controlled temperature and relative humidity. Spectral radiation was measured at the canopy level with a portable spectroradiometer, Licor 1800. Proline concentration and leaves proline were analyzed by spectrometry and the synthesis capacity estimated. Analysis of Variance and the Tukey's Test for p≤0.05 were used to assess proline concentration significance. The results show that proline concentration is a highly varietal dependent factor, not allowing the forthright comparison between cultivars. Nevertheless, a differential seedling plant response between varieties in relation with artificial light application was found. The correlation between leaves proline concentration and spectral regions has been studied, finding two opposite behaviors that serve as a criteria to establish two cultivar groups: group 1 (only 4 cultivars) with a positive correlation with red, far red, photosynthetically active radiation (PAR) and near infrared radiation (NIR) and a negative correlation in blue, and group 2 (eleven cultivars), with the opposite behavior related with proline concentration.