Short-and long-term phenotypic changes of hydroponically grown tomatoes as a result of seedling production substrates

Abstract

Short-and long-term phenotypic changes of hy-droponically grown tomatoes as a result of seedling production substrates were examined. As such, plants were grown for two weeks in three different seedling production substrates: horticultural growing medium on peat basis, perlite, and a 1:1 mixture of peat-perlite, before they were transplanted into a rockwool based hydroponic system. Germination of plants in the perlite treatment resulted in significantly smaller leaves, lower stem diameter and a delayed start of harvesting compared to the other treatments, while no differences in the amount of marketable tomatoes were observed at the end of experiments. The perlite treatment yielded fewer small and blossom end rot fruits. Applying Lichtenthaler’s index and the normal-ized difference vegetation index showed lower chlorophyll concentrations in the leaves of the perlite treatment. The car-ratio index revealed a tighter ratio of carotenoid to chlorophyll in the perlite treatment implying some kind of stress. Due to the absent influence of smaller leaves and assumed lower chlorophyll concentration on yield, a higher photosynthetic radia-tion use efficiency (PRUE) was expected. Applying the photochemical reflectance index, which is correlated to the PRUE, could not support this hypothesis. Re-flectance indices calculated for the optical properties of fruits did not suggest any differences in fruit pig-mentation. It is therefore possible to save a portion of the finite resource peat by using perlite as seedling production substrate without worrying about loss of yield and fruit pigmentation.