Chilling Requirement to Overcome Bud Dormancy In Chokecherry

Chokecherry (Prunus virginiana) is a native North American plant that has the potential of becoming a regionally important alternative fruit crop.  Fifteen open-pollinated seedling populations collected from the Intermountain West were subjected to chilling temperatures (4 °C) for 0, 2, 4, 6, 8 and 10 weeks, and then held under long day conditions (16 h) at 20±2 °C for four weeks.  Bud break and shoot growth were then measured on replicate plants to determine chilling requirement for breaking bud dormancy.  There was no significant budbreak at less than 4 weeks of chilling, whereas plants chilled for 10 weeks showed 100% budbreak.  The amount of chilling required to produce >80% budbreak differed among seedling populations, and ranged from 6 to 10 weeks.  The effect of chilling time on terminal shoot elongation also differed among seedling populations.  Some populations showed maximum elongation after 6 weeks of chilling, whereas shoot elongation in other populations continued to increase through 10 weeks of chilling.  There did not appear to be any correlation between chilling requirement for budbreak, and the effects of chilling on terminal shoot growth.  These results indicate genetic variation in chilling response.  Among these Intermountain West ecotypes, ten weeks of chilling maximized both budbreak and terminal shoot growth.