CHILLING EXPOSURE AND HYDROGEN CYANAMIDE INTERACT IN BREAKING DORMANCY OF GRAPE BUDS

An experiment was conducted to examine the interaction between chillin g exposure (0, 50, 100, 200, 400, and 800 hours at 3C) and hydrogen cy anamide (H2CN2) concentration [0%, 1.25%, and 2.50% (v/v)] on the budb reak of dormant grape buds (Vitis vinifera L. 'Perlette') collected in late fall before the onset of temperatures less than or equal to 13C. Budbreak at 22C was most rapid for cuttings exposed to 800 chill hour s and least rapid for cuttings that received no chilling, Budbreak pf cuttings receiving 50 to 200 hours of chilling was similar and lagged behind that of cuttings exposed to 400 or 800 hours. Maximum observed budbreak improved with increased chilling exposure. Hydrogen cyanamide hastened the growth of all chilling treatments and increased the perc ent budbreak of cuttings receiving less than or equal to 400 chill hou rs, When cuttings were not treated with H2CN2, the number of days requ ired for 50% budbreak declined sharply as chilling exposure increased from 0 to 400 hours,In contrast, this interval was reduced only slight ly as chilling increased from 400 to 800 hours, Hydrogen cyanamide-tre ated buds exhibited a more gradual decline in the number of days requi red for 50% budbreak with increased chilling exposure, In this study, the physiological efficacy and economic benefits of H2CN2 applications diminished with increased chilling exposure.