The effects of Paclobutrazol on the growth, morphology and distribution of dry matter in tomato plants (Lycopersicon esculentum cv. Bellevue)

Abstract

Two experiments were conducted to study the effects of paclobutrazol supplied as a root application (via the nutrient solution) on the growth of glasshouse-grown tomatoes cv. Bellevue. In experiment 1, the plants were treated with paclobutrazol at 0, 10 and 50 ppm for 6 days at the vegetative stage (sixth-leaf stage). Two harvests were subsequently taken at 4 and 6 weeks after treatment. In experiment 2, paclobutrazol at 0, 2 and 10 ppm was applied for 2 or 6 days as a pulse treatment following the emergence of the sixth flower truss. Harvests of plants were taken 2, 5 and 8 weeks after paclobutrazol treatment.

In experiment 1, paclobutrazol caused near permanent stunting of the whole plant and although at 10 ppm limited recovery was observed, the rates were excessive. In experiment 2, paclobutrazol significantly retarded young and newly emerging vegetative shoot growth. At the final harvest, plant height was reduced from 287cm to 2 13cm at both rates of paclobutrazol. Reduced stem length above truss 6 was the major contributor to the stem shortening effect. Lateral shoot growth was also substantially shortened by 37% (2 ppm) and 53% (10 ppm) compared to the untreated. In both instances, stem weight above truss 6 and lateral dry weight components were suppressed to a similar extent at the last two harvests. Reductions in dry weight in response to paclobutrazol were always smaller in comparison to reductions in elongation of the main stem and laterals. This implies a potential for using paclobutrazol to reduce the requirement for manual removal of lateral shoots.

Paclobutrazol had no significant influence on the total flower production but there was a small reduction in fruit set at the final harvest (5% and 13% reduction at 2 and 10 ppm). In addition, the number and dry weight of ripe fruit was increased by 67.8% and 114.1% respectively at 10 ppm paclobutrazol, although the total number of fruit was reduced by 13%.

The results demonstrate that paclobutrazol applied to tomatoes may help reduce manual removal of lateral shoot growth and improve uniformity of fruit ripening. Paclobutrazol may be a useful tool in the management of glasshouse-grown tomatoes.