Abstract
In experiment 1, ‘Kosui’ and ‘Gold Nijisseiki’ pear cuttings that had accumulated various amounts of chilling were treated with 0.5 and 1.0% hydrogen cyanamide or 2.5 and 10.0% hydrogen peroxide. Although the effect of both regents on promoting budbreak depended on their concentration and chilling accumulation, hydrogen cyanamide was more effective than hydrogen peroxide in most chilling values. One point zero percent hydrogen cyanamide applied at Chill Unit (CU) 600 was the most effective for breaking bud dormancy among the treatments. In experiment 2, 0.5 and 1.0% hydrogen cyanamide were used to treat adult ‘Kosui’, ‘Hosui’, ‘Gold Nijisseiki’, and ‘Niitaka’ trees at CU300, 600, 900, and 1,500, and thereafter the percentage of budbreak, pollen development, and the flowering period were observed. The response of budbreak in flower buds to hydrogen cyanamide varies with chilling accumulation and the cultivar. The effective period for ‘Kosui’ and ‘Gold Nijisseiki’ was during CU300 to 900, that of ‘Hosui’ was CU600 to 900, and that of ‘Niitaka’ was CU900. Clear differences in the breaking of bud dormancy were observed among these hydrogen cyanamide treatments. However, pollen growth and flowering were over 2 days earlier than in the untreated control due to the treatment irrespective of broken/unbroken dormancy.
