THE DWARFING EFFECT OF A SINGLE APPLICATION OF GROWTH-INHIBITORS TO THE ROOT-STEM CONNECTION THE COLLAR TISSUE OF 5 SPECIES OF FRUIT-TREES

Five species of one year old potted fruit trees (plum, sour and sweet cherries, apricot and pear) were treated once only, with two growth in hibitors at two doses, or with benzyladenine, (BA) at the surface of t he collar (the vascular transition region) and at the mid-stem, to dim inish growth and enhance fruiting. Paclobutrazol P, (15 mg per tree) a nd 2,3,5-triiodobenzoic acid, TIBA (3.5 mg per tree) significantly red uced shoot length in all five and two fruit species, respectively, ove r three consecutive years. The plum trees cv. Early Prune and sour che rry trees cv. Ujfehertoi Furtos were most responsive to P and TIBA app lications to the collar. The length of the shoots was reduced to almos t one third with P and to half with TIBA compared with the controls in both species. Fruiting of the plum trees treated with P on the collar increased four-fold. When calculated on the basis of tree size, fruit ing was still higher compared with that of larger control trees. Plum and sour cherry trees reduced in size by TIBA treated on the collar al so showed similar results. An advance in flowering time in pear trees and an apparent reduction in number of flowers (due to the reduced tre e size) were observed in sweet cherry and apricot trees after P applic ation on the collar. The TIBA treatment on the collar at a dose of 7 m g per tree markedly increased flowering of the sweet cherry trees but did not affect that of the apricot and pear trees. Also, treatment wit h BA did not affect shoot elongation or flowering but extended the gro wth period of the plum and apricot trees. The growth inhibitors, when applied to the mid-stem, affected neither shoot length nor flowering o r fruiting of four fruit species, the exception being the sour cherry trees whose growth was significantly depressed. The results indicate t hat the collar tissue of fruit trees, especially of plum and sour cher ry species, is a sensitive region of the trunk and the most suitable l ocation for influencing tree growth and fruiting. The minute amounts o f the growth regulators applied are not hazardous to consumers or to t he environment, as they are separated in time and place from fruiting in subsequent years and are applied to the tree not to the soil.