The effect of succinamic acid 2,2-dimethylhydrazide on shoot and fruit growth of Williams' Bon Chretien pear trees

Abstract

Whole-tree sprays of the growth retardant succinic acid 2,2-dimethylhydrazide (SADH) applied in autumn increased the fruit yield of Williams' Bon Chretien pears by 50-20%. Shoot number was reduced by 25-50 %. Delayed flower opening was not observed. The increase in fruiting did not result from the action of SADH in the flower bud during spring. Treatments combining shoot tipping and autumn SADH sprays indicated that competition from shoots resulted in abscission of fruitlets. It was concluded that autumn SADH treatments increased fruit number per tree at harvest by reducing to spurs a substantial number of potentially vigorous shoots. Label movement from single leaves fed with 14CO2 showed that during the 6 weeks following bloom, basal shoot leaves and spur leaves supplied both shoot tips and fruitlets. However, the results indicate that by 3 weeks after full bloom the observed shoot competition for assimilates was not the cause of fruitlet abscission.