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Vigor control in 'McIntosh' apple trees by growth inhibitors

Rufato, L., Brighenti, A. F., Rufato, A. D., Dominguez, L. I., Robinson, T. L.
Acta horticulturae 2017 no.1177 pp. 223-228
Malus domestica, biosynthesis, canopy, color, fruits, gibberellins, growth inhibitors, prohexadione calcium, shoots, trees, vigor
We evaluated the effects of two gibberellin biosynthesis inhibitors [Prohexadione-Ca (Apogee® 250 ppm) and Trinexapac-ethyl (Moddus® 225 ppm)], on shoot growth of mature 'McIntosh'/M.9 apple trees. The growth regulators were applied 7 days after bloom, when shoots were 5 cm long. Shoot length was measured every 15 days to determine growth rate. Shoots were measured in the lower, middle and upper portion of tree and according type (terminal and lateral shoots). The number of fruits tree-1, yield and yield efficiency were determined at harvest. After harvest, fruits were classified according to the color. Both growth inhibitors reduced shoot growth rate approximately 30% and reduced the daily growth rate (cm day-1) of all types of shoots and in all positions of tree. Daily growth rate was affected by shoot position. Growth rate of shoots located in lower portion of tree was reduced more than for shoots in the upper part of the tree. Likewise, terminal shoot growth rate was reduced less than lateral shoot growth rate. Trinexapac-ethyl (Moddus® 225 ppm) increased the number of fruits tree-1 and yield efficiency but reduced return bloom about 57% compared to the untreated control and 65% when compared to Apogee®. Both growth inhibitors had a positive effect on fruit color, which was probably due to improved light penetration into the canopy.