Leaf Gas Exchange and Growth Responses of Mature ‘Fantasia’ Nectarine Trees to Paclobutrazol

Abstract

Abstract Mature trees of ‘Fantasia’ nectarine ( Prunus persica L. Batsch. ‘Fantasia’) were treated with the chemical growth regulator paclobutrazol (PP333) in the spring of 1983. Net photosynthetic gas exchange measurements were conducted on treated and control trees in the field at monthly intervals from May through September. Growth responses were measured at the end of the growing season. The paclobutrazol treatment resulted in a 67.9% decrease in annual extension shoot growth compared to controls and no apparent decrease in fruit yield or leaf photosynthetic rate. Total tree leaf area was reduced at the end of the season by an estimated 54.5% (so total tree photosynthesis may have been reduced). There were no apparent effects of either the presence of fruit or stage of fruit maturity on leaf CO 2 assimilation rate. Newly produced extension shoots on treated trees had shorter internodes, larger diameters, more flower buds per unit length, higher specific shoot dry weights but fewer buds per unit shoot dry weight, than on untreated trees.