PHYSIOLOGICAL EFFECTS OF GIBBERELLIC ACID (GA3) AND PACLOBUTRAZOL (PP333) ON COTTON PLANTS

Abstract

Field experiment was carried out in The Experimental Farm, Faculty of Agric., Ain Shams University during season 2003 and repeated in season 2004 to investigate the effect of the plant bioregulators; GA3 and PP333 at 25 and 50 ppm each on cotton plants Gossypium barbadens L. cv. Giza 85. Bioregulators were applied as soaking treatments presowing (S) or as soaking plus foliar application (S+F) at flowering. Soaking of seeds in PP333 inhibited seedling growth as indicated by the reduction in seedling length, fresh and dry weights, cotyledonary leaf area and delaying the development of true leaves. PP333 at both concentrations reduced total chlorophylls concentration. PP333 at 50 ppm showed the highest values of proline and phenols concentrations in the seedling. The effects of GA3 at 25 and 50 ppm soaking treatment on the developed seedling were mostly insignificant. The inhibitory effects of PP333 at 25 or 50 ppm seed soaking treatments were over when plants reached reproductive stage. Plants received just seed soaking treatments with PP333 showed the same trend of control plants (at 90 days from sowing) on the plant height and root length. Moreover, an increase in plant fresh and dry weights was achieved by PP333 at 50 ppm (S), this effect was significant in the first season. P333 at 50 ppm (S+F) caused reduction in plant height. However, this treatment showed insignificant increase in bolls number and significant increase in seed-cotton yield per plant at harvesting. GA3 at 50 ppm (S+F) treatment was the favorite treatment, showed an increase in root length, fresh and dry weights and fruiting branches number. At harvesting, GA3 at 50 ppm (S+F) increased bolls number, single boll weight and seed-cotton yield weight per plant. GA3 treatments gave higher concentrations of total soluble carbohydrates and proteins than PP333. The effects of different applications of GA3 and PP333 on seedling, plant growth and correlated biochemical constituents were discussed.