The effects of uniconazole, a gibberellin biosynthesis inhibitor, on potted 'smoothee'/MM.106 apple trees

Experiments were conducted to study the effects of uniconazole, a gibberellin biosynthesis inhibitor, on the morphology and physiology of potted 'Smoothee'/MM. 106 apple trees. Increasing rates of uniconazole tended to reduce leader elongation and dry weight accumulation, shoot elongation and dry weight accumulation, and enlargement of leaves. Increasing rates of uniconazole resulted in increased specific leaf weight of new leaves and wider crotch angles of limbs. Stomatal conductance of the new leaf (newest, fully expanded leaf) tended to be increased at three weeks after treatment with increasing rates of uniconazole. The stomatal conductance of both the old and new leaf were greater than the control for all treatments during the first season after treatment with uniconazole. Similarly, transpiration rates were greater at three weeks after treatment for trees receiving the highest rates of uniconazole. Transpiration rates of both old and new leaves were greater for trees receiving the highest applications than for the control trees. Trees receiving 300 and 400 mg liter^-1 uniconazole had higher daily maximum net photosynthetic rates (Pn) for the new leaf, whereas applications of 100 and 300 mg liter^-1 uniconazole had higher daily maximum Pn rates for the old leaves. However, the two greatest applications enabled both the old and the new leaves to maintain higher Pn rates during the afternoon. The Pn rates of the new leaves tended to be higher at greater rates of uniconazole application as soon as three weeks after treatment. The old leaves had higher Pn rates during the first season after treatment, however this trend was not as noticeable for the new leaves.