Effect of gibberellin and auxin on parthenocarpic fruit growth induction in the cv micro-tom of tomato

The effect of applied gibberellin (GA) and auxin on fruit-set and growth has been investigated in tomato (Solanum lycopersicum L.) cv Micro-Tom. It was found that to prevent competition between developing fruits only one fruit per truss should be left on the plant. Unpollinated ovaries responded to GA(3) and to different auxins [indol-3-acetic acid, naphthaleneacetic acid, and 2,4-dichlorophenoxyacetic acid (2,4-D)], 2,4-D being the most efficient. GA(3)- and 2,4-D-induced fruits had different internal morphology, with poor locular tissue development in the case of GA, and pseudoembryos development in the case of 2,4-D. Also, GA(3) produced larger cells in the internal region of the mesocarp (IM) associated with higher mean C values, whereas 2,4-D produced more cell layers in the pericarp than pollinated fruits. The smaller size of GA(3)- compared with 2,4-D-induced fruits was due to them having fewer cells, only partially compensated by the larger size of IM cells. Simultaneous application of GA(3) and 2,4-D produced parthenocarpic fruits similar to pollinated fruits, but for the absence of seeds, suggesting that both kinds of hormones are involved in the induction of fruit development upon pollination. It is concluded that Micro-Tom constitutes a convenient model system, compared to tall cultivars, to investigate the hormonal regulation of fruit development in tomato.