A CHILLING MODEL TO ESTIMATE REST COMPLETION OF ERECT BLACKBERRIES

The time of rest completion of ‘Apache’, ‘Arapaho’, ‘Chickasaw’, ‘Darrow’, ‘Kiowa’, ‘Navaho’, and ‘Shawnee’ blackberry (Rubus subgenus Rubus Watson) buds was compared and various models for estimating chilling were evaluated. ‘Kiowa’ and ‘Arapaho’ buds had the shortest rest periods, while those for ‘Shawnee’, ‘Navaho’, and ‘Chickasaw’ buds were intermediate. ‘Apache’ and ‘Darrow’ buds had the longest rest periods.
The model that accounted for the variation in percent budbreak among cultivars and temperatures during two dormant periods had the following two components: 1) a chilling inception temperature of -2.2EC and 2) weighted chilling hours that accumulated after the chilling inception temperature.
The chilling hours in this model were weighted as follows: 0 to 9.1EC =1; 9.2 to12.4EC = 0.5; 12.5 to 15.9EC = 0; 16 to 18EC = -0.5; >18EC = -1. This study also elucidated that a blackberry model with a chilling inception temperature of -2.2EC estimated chilling more accurately than one with chilling inception just after the maximum negative accumulation of chill units as used in the Utah chilling model.
Also, temperatures between 0 and 2.4EC must be weighted more heavily in a blackberry model than in the Utah peach model to accurately estimate chilling and rest completion.

IX International Rubus and Ribes Symposium

M.R. Warmund, J. Krumme

Rubus, chill units, cold requirement, endodormancy

https://doi.org/10.17660/ActaHortic.2008.777.41