Exogenous dormancy-breaking substances positively change endogenous phytohormones and amino acids during dormancy release in ‘Anna’ apple trees

A 2-season trial was conducted to verify the effects of foliar applications of some dormancy-breaking substances (DBS) on dormancy release in buds of ‘Anna’ apple (Malus sylvestris, Mill) trees, as well as on metabolic changes in the contents of phytohormones, proline and arginine in buds during their release from dormancy. The efficiency of early bud break induced by Dormex™, potassium nitrate, mineral oil, calcium nitrate and thiourea was noticed in varying degrees. Although Dormex™ was distinguished, all DBS hastened bud break, shortened flowering duration, improved bud break% and fruit-set%, increased the contents of gibberellic acid, indole-3-acetic acid, proline and arginine, but reduced abscisic acid content in buds as compared to the control. These results were positively reflected in the final tree yield. Accordingly, it is concluded that the use of Dormex™, at a rate of 4 %, could be recommended for reaching bud break as early as possible and improving ‘Anna’ apple tree yield under the short winters in Egypt and similar regions by regulating the contents of proline, arginine and phytohormones in buds.