EFFECT OF HIGH-TEMPERATURE TREATMENT ON BREAKING OF BUD DORMANCY IN JAPANESE PEAR NIJISSEIKI

Dormant 'Nijisseiki' pear cuttings were treated with 20% calcium cyana mide, an anaerobic condition and high temperature (45-degrees-C) . ABA levels in the leaf buds of the pear cuttings were determined after th ey were chilled (5-degrees-C) for 0, 400, 800 and 1,200 hr and then ex posed to the high temperature treatment. Actinomycin D was injected in cuttings before or after high temperature treatment. 1. Leaf and flow er buds were released from endodormancy by exposure to 45-degrees-C fo r 4 hr, whereas buds in ecodormant stage failed to push given the same treatment. Dormancy of flower bud on 'Nijisseiki' pear tree and that of leaf and flower buds on cuttings was broken by exposure to 45-degre es-C for 4 hr an accumulation of 500 Chill units (A chill unit is an h our under 0-degrees approximately 10-degrees-C) . There was no signifi cant difference between the percentage bud break of calcium cyanamide- treated trees and that of the control. 2. ABA level in leaf buds decre ased after exposure to 45-degrees-C for 4 hr following 0 and 400 hr ch illing; however it increased in buds exposed to 800 and 1, 200 hr of c hilling. 3. Effect of high temperature treatment was reversed by pre-t reatment whit Actinomycin D, whereas post-treatment with Actinomycin D did not do so.