| Abstract: |
The present investigation has been carried out on Washington navel orange (Citrus sinenses) trees budded on sour orange rootstock during the successive seasons of 2008, 2009, 2010 and 2011. Eighty four, ten years old, trees were used in this investigation. In 2008 & 2009 the trees were equally distributed between 14 treatments, which were the possible combinations between two irrigation rates (IR) (4000 & 6000 m3 / fed./year) and seven growth regulator (GR) treatments (i. e. control, Auxs. (naphthyl acetic acid 0.45 % and naphthyl acetamide 1.25%)10 ppm, Auxs. 20 ppm, GA3 10 ppm, GA3 20 ppm, Auxs. 10 + GA3 10 ppm and Auxs. 20+ GA3 20 ppm).. Each treatment was represented by 6 trees. Results of 2008 &2009 seasons made possible to use higher irrigation rates (6000 & 8000 m3/ fed. / year) and higher gibberellin and auxins concentration (40 ppm). As such, treatments experimented in 2010 &2011 were the possible combinations between two irrigation rates (6000 & 8000 m3 / fed. /year) and five growth regulator treatments(i. e. control, Auxs. 20 ppm, Auxs. 40 ppm, GA3 20 ppm and GA3 40 ppm). So, 60 experimental trees were used in each of 2010 & 2011 seasons.The results showed that increasing IR, generally, enhanced tree vigor as well as flowering, fruit set, fruit retention after June drop, yield, fruit quality and roots characteristics. The tested GR treatments exerted significant effects on flowering, fruit set, fruit retention, yield, fruit quality but did not affect fibrous roots characteristics or most of tree vigor characteristics. The best results of the interaction between irrigation rate and growth regulator treatments came, in most cases, from the highest irrigation rate with the highest concentration of Auxs. specially with the yield and fruit quality characteristics.
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