Abstract
Prohexadione-Ca (calcium 3-oxido-4-propionyl-5-oxo-3-cyclohexene carboxy-late), an inhibitor of distinct deoxygenase which catalyses the last steps of GA metabolism and the hydroxylation of flavanones, has been found to control vegetative and cropping performance and to counteract some pathogen infections (scab and fireblight) in apple and pear. To further evaluate these effects, prohexadione-Ca was tested under northern Italian climatic conditions on two pear varieties of differing vigour (William/Kirkensaller, Abbé Fétel/Beurré, and Hardy/Quince C). Prohexadione-Ca was applied at different concentrations and application schedules (50 ppm x 4 times and 125 x 3 and x 4 times) starting from 5-cm shoot length up to the onset of secondary bloom. Data were collected on vegetative, cropping, fruit quality parameters and incidence of Erwinia amylovora in field conditions. Prohexadione-Ca controlled vegetative growth on both cultivars, although the effects were related to the differing vigor of the cultivar-stock combinations. Cropping performance was also affected: on the vigorous William/Kirkensaller, yield was increased by the concentration while average fruit weight was unaffected; on Abbé Fétel/Quince C, prohexadione-Ca was ineffective on yield/tree but significantly increased average fruit weight.