INFLUENCE OF THE PRUNING FOR GRAFTS ON COLD RESISTANCE OF MOTHER TREES

摘要

During the last 5 years the production of certified planting material in Bulgaria has been synchronized with the European standards. In cooperation with Germany mother orchards for grafts have been established in the towns of Plovdiv, Kyustendil, Sliven and Troyan. An object of study is the strong pruning of the mother trees of stonefruit species in the orchard of the IUSA, Troyan and its influence of their cold resistance. The greatest damages caused by the long frosts (7 days with a temperature of-29°C) were found in peach, apricot and some cherry varieties. Frost killing was also recorded in some plum trees. In apricot, cherry and plum the damage degree also depended on the pruning strength of the mother trees, the injuries being heaviest for total pruning of all annual shoots for grafts. Leaving of shoots with all their leaf mass increased the cold resistance of the mother trees. Generally speaking there is a direct relationship between the frost resistance and growth processes. It was foundthat when pruning for grafts it is obligatory to leave without pruning annual shoots on the mother trees that will maintain the nutrient balance between leaves, roots and stem. The exact ratio between pruned and unpruned shoots is to be determined, but for the time being total pruning for grafts should not be practised because it strongly decreases the cold resistance of mother trees of stonefruit species.