Effect of Chilling Treatment on Intensity of Bud Dormancy, Respiration and Endogenous Growth Regulators in Japanese Pear 'Nijisseiki'.

Abstract

In Exp. 1, 'Nijisseiki' pear cuttings were chilled at 5-degrees-C for 0, 300, 500, 800, 1000, 1100, 1200, 1250, 1300, 1350, 1400 and 1450 hr. After exposure to chilling, the intensities of leaf bud dormancy, the rate of CO2 evolution, and the levels of endogenous growth regulators were determined. In Exp. 2, 2-year-old 'Nijisseiki' trees were kept in the greenhouse in October and November; the control trees were kept outdoor. The levels of free and bound ABA in the floral primordia and bud scales were determined in February. Exp. 1. 1. Buds were in their deepest dormant state up to 800 hr of chilling. The intensity of bud dormancy decreased after 800 to 1350 hr of chilling; dormancy was completely satisfied after 1400 hr of chilling. 2. The concentration of ABA decreased proportionately to the number of hours of chilling up to 800 hr. A rapid increase in GA-like substances was detected in the buds after 1200 hr of chilling which was followed by equally rapid increases in cytokinin-like substances and IAA in that order. CO2 evolution increased gradually after 1100 hr of chilling while ethylene evolution increased after 1250 hr of chilling. Exp. 2. 1. Levels of free and bound ABA were higher in the floral primordia collected from trees growing in the greenhouse than those sampled from field-grown trees. There was no significant difference in free ABA content of bud scales sampled from greenhouse-grown trees and those collected from field-grown trees. These results indicate that the decrease in ABA level induced by chilling is closely related to bud dormancy in Japanese pear.