Isoda, A., H. Nakazato, H. Nojima and Y. Takasaki (Faculty of Horticulture, Chiba University, Matsudo-city, Chiba 2 7l-8510, Japan)

Abstract: Five cultivars, including Virginia (Chibahandachi and Chiba 43), Spanish (Kintoki) and Valen-cia (Valencia) types, and a derivative (Nakateyutaka) from the cross between Virginia and Spanish types, were grown under field conditions. At the early pod growth stage, paclobutorazol, which prevents endogenous gibberellin synthesis, was applied to suppress the growth of the shoot and to improve partitioning of dry matter to pods. Pod dry weight of the treated plants was greater as compared to the control, with smaller stem dry weight. The plant height of the treatment was decreased due to shortening internode length. Leaf area of the treated plants was distributed densely at the upper layers of the canopy as compared to the control, since the leaf area indices were not changed and the internode length was decreased by the treatment. In the yield and yield components except one seed weight, the treated plants were greater than those of the control, although there was no significant difference. Among the five cultivars, Nakateyutaka had the greatest effects of the treatment on pod and seed yield. The Virginia types and the derivative from the cross between Virginia and Spanish types showed large effects of the paclobutorazol treatment in terms of increasing percentages of pod dry weight and pod yield as compared to Spanish and Valencia types.