Foliar boron application improves flower fertility and fruit set of olive

A 2-year field study was conducted to determine if foliar B applications pr ior to flowering increased fruit set in olive (Olea europaea L.) cv. Manzan illo. Boron solutions were applied (935 L.ha(-1)) at four concentrations (0 , 246, 491, and 737 mg.L-1) to trees exhibiting no vegetative symptoms of B deficiency. Foliar B application increased both the percentage of perfect flowers and fruit set, but no effect on pollen germination was observed in either year. The increase in fruit set was not accompanied by a reduction i n fruit size. The beneficial effects of foliar B application varied between years and were greater when fruit set was low. The results obtained here a re in agreement with those observed in other tree species, in which foliar B applications made immediately prior to flowering or during the period of floral bud initiation significantly increased fruit set and yield. The phys iological basis for this effect, however, remains unclear.