OSMOTIC STRESS, YIELD AND QUALITY OF HYDROPONIC TOMATOES

In heated greenhouse studies during the winter tomato plants were grown hydroponically at a range of osmotic levels using either the Nutrient Film Technique (NFT), or a pumice based system in which nutrients were applied to waste in a similar manner to a rock wool system. Four osmotic levels were used in the NFT study (2,4, 6 & 8 ms cm^-1) and 2 levels in the pumice study (2 & 4.5 ms cm^-1). In the first study 4 cultivars, namely Belcanto, Counter, Liberto and Rondello were used. The osmotic treatments commenced at the time of anthesis of the first flower on the first truss. All the cultivars used were indeterminate types and of European origin. In the NFT study the plants were stopped 2 leaves above the first truss, while in the pumice the plants were grown as a multi-truss crop to a height of 2m.

In the second study three distinct fruiting types, namely Cherita (cherry), Rondello (standard), and Ophir (beefsteak) were used.

In all studies fruit yields were found to fall with increasing osmotic level primarily due to a reduction in fruit size, but the quality of the fruit (measured both in the laboratory and organoleptically) was found to improve with increasing osmotic level. In the first single truss study water use decreased, and the leaf area fell with increasing osmotic levels.

Cultivar differences were found in total fruit yield in both single truss studies, but not in the multi-truss experiment. This may be due to yield being source limited in the multi-truss study, but sink limited in the single truss experiment.