Chilling Response of Arkansas Blackberry Cultivars

Abstract

Floricane-fruiting blackberries ( Rubus subgenus Rubus, Watson) require a period of chilling (hours below 7°C) during the dormant season to resume growth in the spring. Chilling requirement is cultivar dependent. The University of Arkansas blackberry breeding program includes efforts to identify genotypes better adapted to low-chill climates. In this study, experiments were conducted to evaluate response to artificial chilling in whole blackberry plants, to develop a technique for determining chilling requirement using stem cuttings, to use this technique to define the chilling requirements of some currently available blackberry cultivars, and to determine whether plant age has a bearing on chilling requirement. The response to chilling in whole plants was consistent with that in stem cuttings for both a high-and low-chill cultivar indicating that stem cuttings may be used to determine chilling requirement. The cultivars evaluated had significantly different chilling requirements as determined by the stem cutting technique. ‘Kiowa’, ‘Ouachita’, and ‘Prime-Jim’ ^®, had a low chilling requirement (100-300 h), ‘Arapaho’, ‘Choctaw’, and ‘Shawnee’ had a medium chilling requirement (300-600 h), and ‘Navaho’, ‘Chickasaw’, and ‘Apache’ had a high chilling requirement (700 h or more). The exact chilling requirements for the high-chill cultivars were not clear from our data due to poor budbreak in the stem cuttings. The results of this study indicated that stem cuttings can be used to broadly determine chilling response in low, medium and high-chill blackberry cultivars, but variability in budbreak may make it difficult to pinpoint an exact chilling requirement.