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Abstract
Boron plays a major role in plant growth and development. It is required for flower fertility, fruit set and high yield of olive. Boron deficiency is a common micro-nutrient disorder in olive orchards. Olive is sensitive to the lack of boron. This investigation was undertaken to study the effect of times and concentrations of B foliar application on olive (Olea europea L.) tree growth, flowering, fruit set, yield, tissue boron and phenol content, chlorophyll content, total soluble sugars and endogenous hormones (GA3, ABA, IAA) content. Boron foliar fertilization was applied to twenty years old boron deficient olive trees (cv. Frantoio) for two successive years, 2010/2011 and 2011/2012 at the Nuclear Research Center Experimental Farm, Inshas, El-Qaliubiya Governorate, Egypt. Treatments included 6 boron concentrations (0.0, 100, 200, 300, 400, 500 mg.L-1) applied at flower initiation (1st November), one month after flower initiation (1st December) and two month after flower initiation (1st January). Boron was applied as boric acid. Nitrogen translocation and distribution under boron foliar application was also studied using 15N-labeled (NH4)2SO4 and stem injection technique. The obtained results indicated that boron was significantly effective in increasing vegetative growth, flowering, fruit set, yield, oil percentage and oil yield. The highest increase in all previous traits was achieved by 200 mg.L-1 boron concentration applied at January. All boron treatments increased leaf, bud and fruit boron content comparing with the control. This increase in tissue boron content was linear