NASHI PEAR (PYRUS PYRIFOLIA) DORMANCY UNDER MILD TEMPERATURE CLIMATE CONDITIONS

Abstract

Temperature is the main climatic factor controlling the beginning and the ending of dormancy. Nashi pears grown under mild winter present extended period of blooming, bud break, and vegetative growth compared with pears grown under normal winter conditions. When grown under mild winter, Nashi pears develop physiological disorder, which is associated to reducing number of flowers per bud. Chilling requirement for Nashi pear has been previously reported. Temperatures from 3 to 10°C seem to be as effective as 5°C. Chilling interruption negatively affects bud break. Effective temperature for bud break differs among cultivars. As in Southern Brazil number of chilling hours varies from 550 to 950, according to location and year, bud break and blooming differ among main Nashi pears resulting in poor cross-pollination. Mineral oil plus hydrogen cyanamide, branch bending and girdling have been used for bud breaking and blooming. Without chemical treatment 'Housui' and 'Kousui' present delayed and poor bud break. For 'Nijisseiki', increasing chilling up to 1,440 hours results in higher percentage of bud break and flower number per bud. Blooming of Nashi pears may occur 10 to 15 days ahead of normal blooming date according to the timing of mineral oil and hydrogen cyanamide treatments. Models to predict hardness of dormancy are tested as a means to establish best timing of chemical treatment.