Regulación de la carga frutal en agroecosistemas de perales mediante programas de extinción de frutos.

The objective of this investigation was to regulate fruit tree crop through fruit extinction. To do that in two different agroecosystems of pear trees cv. Williams the following treatments were applied in a complete randomized design: 1: 6-Benzyladenine (BA): 200 ppm when mean fruit diameter (FD) was 20 mm; 2: BA 150 ppm at 14 mm FD; 3: BA 75 ppm at 7 mm FD + another application of BA 75 ppm at 14 mm FD; 4: Urea 7,5 % at 80 % full bloom; 5: Urea 7,5 % at 80 % full bloom + another application of BA 75 ppm at 14 mm FD; 6: Control: hand thinning. Response variables were: number of fruit per cm2 Branch Cross Sectional Area (BCSA) and per 100 flower clusters; fruit set distribution (percentage of spurs where fruit set was 0, 1 or +1) and number of hand thinned fruits per cm2 BCSA. At harvest, fruits were classified according to commercial sizes of the standard box (18,2 kg). Data were analyzed using the procedure of analysis of Variance; Chi-square test and principal component analysis. Trees treated with BA had higher fruit extinction using doses of 150 ppm at 14 mm FD or with repeated application of 75 ppm at 7 and 14 mm. 200 ppm of BA at 20 mm FD were not effective. Urea treatments did not regulate crop load. A higher percentage of fruit with big sizes were observed in the BA treated trees. In one of the plots, repeated application of BA at 75 ppm showed the highest percentage of fruit big sizes (110, 120 and 135); these three sizes together were 58,12 % of the harvested fruits of this treatment. In the other plot, Urea + BA at 75 ppm had the highest percentage of these three sizes.