Improving productivity of four fruit species by growth regulators applied once in ultra-low doses to the collar

Abstract

SummaryTwo growth retardants: paclobutrazol (P, Cultar) or 2,3,5-triiodobenzoic acid (TIBA) were applied once alone, or in mixtures (in a range of 5 to 20 mg per tree) to the collar of maiden plum, sour and sweet cherries and apple trees, in early spring of the second year after planting. Plum and apple trees were also treated with benzyladenine (BA) at 10 mg per tree a.i. in a mixture with P or TIBA. Sweet and sour cherry trees were treated with natural phenolic substances: phloridzin (Phi) and quercetin (Que) alone, or in mixtures with P and TIBA. A mid-stem treatment with P and shoot bending were also applied to the plum and apple trees for comparison. Measurements of tree growth and fruiting were made within 4 or 5 years. The reaction of the four species to the treatments varied according to the growth regulator applied. Plum trees responded mostly to TIBA and its mixtures with P. A strong suppression of tree growth and increased fruit productivity, as well as improved fruit quality, were observed. The TIBA application and its mixtures with P were also effective in causing growth reduction of the sweet cherry trees. Treatments with P alone, or mixed with TIBA, were effective in growth limitation of sour cherry trees. Some increase in the reproductive processes was observed only after the TIBA treatment in both species. The apple trees responded to application of mixtures of TIBA with benzyladenine (BA), or with P, and to P alone, with effective growth reduction. But only the P + BA treatment increased significantly the fruiting of apple trees, while the other treatments resulted in crops proportional to the diminished tree sizes. The mid-stem treatment did not affect plum trees but increased growth of apple trees. Shoot bending had no effect on the plum trees but increased fruiting of apple trees. The addition of Phi to half the lower P dose or TIBA, magnified growth suppression in the sweet and sour cherry trees. When applied alone Que caused a small growth inhibition but Phi produced some increase in growth of sour cherry trees. Results obtained show the possibilities of practical applications of growth regulators to the collar. Their reduced doses mixed with natural phenolic substances are equally effective in growth suppression and make fruit production safer and more profitable, especially in plum and sour cherry trees.