Two concentrations of GA3 were used alone or with 0.5% urea i.e. (50 and 100 ppm) and three levels of potassium nitrate (KNO3) 2 ،4 and 6% were tested as foliar sprays at different times i.e. first time application at full bloom stage , the second time application was at fruit diameter from 1.5-2.0 cm and (first and second time of application) for investigation their effects on fruit set, yield, fruit quality and splitting of 40-years-old Washington navel orange (Citrus Sinensis), trees budded on Sour Orange (Citrus aurantium, L.Osbeck) rootstock during 2008 and 2009 seasons. Data indicated that, all treatments increased fruit set, yield and fruit quality and decreased fruit splitting as compared with control treatment. Data also revealed that, foliar sprays of trees by (GA3 at 50 ppm) with or without 0.5% urea were superior for inducing the highest increase of fruit set and yield, in addition KNO3 at 4% comparing with 2% and 6%. Also, KNO3 treatments increased fruit size, peel thickness and juice acidity especially with high concentrations; on the other hand, the use of GA3 at 50 or 100 ppm alone or with 0.5% urea increased fruit T.S.S and reduced nitrite and nitrate contents in fruit juice as compared with KNO3 treatments. Moreover, it is noticed that trees sprayed at first application or first and second time of application gave the best results, while second application was the best for reducing fruit splitting.

It could be recommended the best treatment for increasing yield and gave high fruit quality is GA3 at 50 ppm with or without 0.5% urea at full bloom stage especially in respect with reducing nitrite and nitrate in fruit juice, and use KNO3 4% at the second time of application to reduce fruit splitting. [Abd El-Rahman,G.F.; Hoda, M.Mohamed and Ensherah, A.H.Tayh. Effect of GA3 and Potassium Nitrate in Different

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Abd El-Rahman, G.F. Hoda, M.Mohamed and Ensherah, A.H.Tayh
Citrus Department, Hort. Res. Instit., Agric. Res. Center, Giza, Egypt