Effect of 1-naphthaleneacetic acid concentrations and the number of its applications on the yield components, yield and fibre properties of Egyptian cotton (Gossypium barbadense L.)

Field experiments were performed in two successive seasons at the Experimental Station, Faculty of Agriculture, Cairo University, Giza, Egypt, on the Egyptian cotton cultivar Giza 75 (Gossypium barbadense L.). Cotton plants were sprayed with the growth regulator 1-naphthaleneace acid (NAA) once (at 90 days), or twice (at 90 and 105 days) or thrice (90, 105 and 120 days) after sowing, during the square initiation and belling stage at the concentrations of 5, 10, 15, 20 or 25 p.p.m. The volume of solution was the same for all treatments, 960 l ha(-1). The control plants were sprayed with water only. The effect of the previous treatments on yield components, cotton yield and fibre properties was studied. The application of NAA increased the number of opened bells plant(-1), bell weight, seed index, seed cotton yield plant(-1) and seed cotton and lint yields ha(-1). The most significant effects were obtained with the 15 and 20 p.p.m. concentrations. Lint percentage, fibre length parameters and micronaire value were not significantly affected by NAA. Flat bundle strength was significantly affected by NAA but with no definite trend. The application of NAA twice or thrice tended to give the best results on yield components and cotton yield compared with one application The results of this study suggested that 20 p.p.m. of NAA gave the best figures when applied twice on the Egyptian cotton plants.