Effects of Paclobutrazol on Dry Matter Accumulation and Grain Filling of Castor Bean

Castor bean (Ricinus communis L.) as a bioenergy crop, received more and more attention in recent years. However, the yield of castor bean seeds is affected by adverse environmental conditions. The objective of this study was to assess the effects of exogenous application of Paclobutrazol (PBZ) on castor bean growth, yield and physiology as well as on its response to environmental stress during grain filling. In the present field study, three PBZ concentrations [0 g？ha-1 (control), 75 g？ha-1 and 150 g？ha-1] were applied twice, once at grain filling of main panicle and once at grain filling of branched panicle. The growth and physiological responses of castor bean were measured four times throughout flowering and seed formation stages [1-early initiation stage of main inflorescence (E), 2- anthesis of main inflorescence (A), 3-maturity of main panicle (M) and 4-maturity of branched panicle (B)]. Plant growth was not affected by the application of PBZ, but leaves remained later on the plant when 75 g？ha-1 of PBZ was applied. With the application of PBZ, the concentration of starch was higher in panicles than in leaves and stems. Also, PBZ application increased the number of seeds per plant without affecting seed size and weight. These results suggest that exogenous application of PBZ can enhance sink strength of panicles and improve seed yield and that application of PBZ at flower initiation can alter photosynthetic partitioning in favor to seed production. On the other hand, PBZ had no effect on antioxidant enzyme activity in the seeds in response to stress