Stem direction affects the fruit yield, plant growth, and physiological characteristics of a determinate-type processing tomato (Solanum lycopersicum L.)

The aim of this study was to investigate whether vertical or horizontal training of the main stem of the determinate-type processing tomato 'Shuho' (Solanum lycopersicum L.) through physical stimulation affects its yield, growth, and physiological characteristics. There was no difference in the total fruit yield and fruit number per plant between the two training directions, but fruit yield, fruit number at 11 weeks after transplanting, and the marketable fruit percent were higher in vertically-trained plants. Furthermore, the stem length increased, the stem diameter decreased, and the lateral shoots at the sixth to seventh and first to fourth nodes were longer in vertically-trained plants due to a positive association between lateral shoot elongation and the concentrations of indole-3-acetic acid, isopentenyl adenine riboside, and isopentenyl adenine. Vertical training, if compared to horizontal one, also resulted in an increased leaf area and photosynthetic rate in the seventh true leaf, bleeding sap rate of the xylem, and dry weights and nitrogen, phosphorus, and potassium contents of the leaf, stem, upper lateral shoots, and roots. These results suggest that vertical training of the main stem is more efficient than horizontal training for increasing the marketable fruit ratio and initial fruit yield of processing tomatoes because it induces morphological changes and increased vegetative growth.