Growth and cropping of ‘Blanquilla’ pear trees treated with paclobutrazol

SummaryThe application of 1000 or 2000 mg l–1 paclobutrazol at full bloom or when shoots were 25 cm long, to trees carrying no crop, inhibited shoot growth, the effect increasing linearly with the concentration applied. However, total tree growth, measured by the relative increase in trunk cross-sectional area, was greatest in the treated trees. The application of paclobutrazol at full bloom resulted in a great reduction of fruit set and in the almost total loss of crop. However, when it was applied in conjunction with GA3, the effect was overcome and a normal crop was obtained. Microscopical observations on flowers sprayed with paclobutrazol showed that growth of ovules and nucellus was slowed down and the maturation of embryo sacs was retarded, effects that were overcome with the application of GA3. Growth of trees treated at bloom time with paclobutrazol was greater than that of trees either sprayed with paclobutrazol and GA3 or left unsprayed, and this was attributed to the loss of crop. Paclobutrazol also reduced fruit size in spite of the very small crop, flattened its shape, and altered other fruit quality parameters.