Tomato Early Seedling Height Control Using a Paclobutrazol Seed Soak

Abstract

Tomato seedling hypocotyls elongate rapidly after germination resulting in weak seedlings. The effects of 0, 250, 500, 750, or 1000 mg paclobutrazol (PB)/L seed soak and soaking times from 1 to 12 hours on tomato (Solanum lycopersicum L.) seed germination, seedling growth, and plant growth were tested. Adequate height control was obtained with 250 mg PB/L while soaking time did not affect seedling growth. In a second experiment, PB was tested at 0, 50, 100, 150, 200, or 250 mg PB/L soaking the seed for 1 hour. A concentration of PB at 100 mg·L–1 provided optimum control of hypocotyl elongation with minimal residual effect on subsequent plant growth. In a third experiment, seed soaked at the different PB concentrations were germinated and grown under light intensities of 0.09, 50, 70, or 120 μmol·m–2·s–1. Seedlings grown under 0.09 μmol·m–2·s–1 were not affected by PB treatment and did not develop an epicotyl. PB seed soak treatment gave greater growth suppression under 50 μmol·m-2·s-1 than under the two higher light levels. Soaking tomato seeds in 100 mg PB/L for 1 hour prevented early hypocotyl stretch of tomato seedlings with no long term effects on plant growth. This treatment effectively prevented excessive hypocotyl elongation when seeds were germinated under low PAR while not over controlling elongation under high PAR conditions.