Recovery of Declined Pear Tree Vitality through Grafting with Scions from a Vigorous Cultivar

Abstract

Taiwan, located in subtropic regions, naturally is not an ideal region for temperate-zone fruit trees' production due to the supra-optimum temperature, heavy rainfall, and higher relative humidity in summer and insufficient chilling in winter. Higher relative humidity and temperature in summer and autumn months cause excessive vegetative growth, resulting in poor flowerbud initiation and formation. Typhoon invasions result in the severe damage of twigs as well as the loss of quality and yield of fruits. In order to overcome these natural barriers, Hengshan (Pyrus serotina Rehd.) pear has been selected as a major cultivar for lowlands in Taiwan. It has low-chilling requirement and higher temperature tolerance. Branches of Hengshan are pulled and tied to a horizontal wire net to adapt to the environmental status. This trellis system enhances flowerbud initiation through the retardation of vegetative growth. It also induces numerous water shoots. Scions from high-chilling cultivars grown at a high altitude on mountains are grafted onto water shoots of Hengshan pear trees. The system has been successful in the production of both high-chilling pears in June and the Hengshan pears in August, and has made production of both pears an important industry in Taiwan. Heavy load and trellis systems, however, result in hastening the senescence of Hengshan trees. Vitality of trees could be restored by grafting scions from a vigorous cultivar, P. koehnei, onto the terminal position of the branches. The practice resulted in several advantages including: 1) uniform growth of branches, 2) redistribution of water shoots, 3) inducing formation of calluses on old damaged trunks, 4) quick recovery of mealybug-damaged branches, 5) rejuvenation of branches, and 6) termination of dormancy.