EFFECT OF 1-NAPHTHALENE ACETIC-ACID CONCENTRATIONS AND THE NUMBER OF APPLICATIONS ON THE YIELD COMPONENTS, YIELD AND FIBER PROPERTIES OF THE EGYPTIAN COTTON (GOSSYPIUM BARBADENSE L.)

Field experiments were performed in two successive seasons at the Expe rimental Station, Faculty of Agriculture, Cairo University, Giza, Egyp t, on the Egyptian cotton cultivar Giza 75 (Gossypium barbadense L.). Cotton plants were sprayed with the growth regulator l-naphthalene ace tic acid (NAA) once (90 days after planting (DAP)), or twice (90 and 1 05 DAP) or three times (90, 105 and 120 DAP), during the square and be lling stage). The concentrations 5, 10, 15, 20 or 25 ppm were used. Th e 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 pre vious treatments on yield components, cotton yield and fibre propertie s was studied. The application of NAA increased the number of opened b olls/plant, boil weight, seed index, seed cotton yield/plant and seed cotton and lint yields . ha(-1). The most significant effects were obt ained with the 15 and 20 ppm concentrations, when each was applied twi ce. Lint percentage, fibre length parameters and micronaire value were not significantly affected by NAA. Flat bundle strength was significa ntly affected by NAA but with no consistent trend. The application of NAA twice or three times tended to give the best results on yield comp onents and cotton yield compared with a single application. The result s of this study suggested that 20 ppm of NAA gave the best figures whe n applied twice on the Egyptian cotton plants. ((C) Inra/Elsevier, Par is.)