Chilling Requirement to Overcome Bud Dormancy in Intermountain West Chokecherry Ecotypes

Chokecherry (Prunus virginiana L.) is a native North American plant that has potential as a regionally important alternative fruit crop. Seedlings from 13 open-pollinated populations were subjected to chilling temperatures (4 degrees C) for 0, 2, 4, 6, 8, 10, 12, 14 and 16 wk, and then held under lone day conditions (16 h) at 20 +/- 2 degrees C for 4 wk. Bud break and shoot growth were then measured on replicate plants to determine chilling requirement for breaking bud dormancy. No significant bud break occurred when seedlings were chilled for less than 4 wk, whereas plants chilled for 10 wk showed 100% bud break. The amount of chilling required to produce 50% bud break (CB(50)) differed among seedling populations, and ranged from 3.1 to 8.9 wk. The effect of chilling time on terminal shoot elongation also differed among seedling populations. Some populations showed maximum shoot growth after 8 wk of chilling, whereas shoot elongation in other populations continued to increase through 16 wk of chilling. For those populations that reached an obvious maximum growth within 16 wk of chilling, a chilling time to obtain 50% of maximum growth (CG(50)) was calculated. There was no correlation between CB(50) and CG(50). For the majority of the Intermountain West ecotypes tested, 10 wk of chilling at 4 degrees C maximized both bud break and terminal shoot growth.