Evaluation of Heat Requirement and Growth Parameters of Three Cultivars of Blackberry (Rubus sp.) under climatic conditions of Sari, Iran

Each plant requires specific amount of heat units complete its growing season. In this study, the heat units of different phenological stages of three cultivars of black raspberry have been investigated. After maintaining the chilling requirement, the studied cultivars were transferred to the greenhouse. The cultivars; Silvan (early), Marion (medium) and Topai (late) spent 91, 109 and 118 days from planting to harvest in the greenhouse, respectively. The results showed that the heat requirements of different raspberry cultivars to complete the phonological stages are different from each other. Early black raspberries variety has a lower heat requirement of 43,000 Cumulative Degree Growth Hours (CGDH) and produce larger fruits than their parent medium maturing variety with a heat requirement 51,000 CGDH. Under the climatic conditions of Sari, early maturing cultivars showed the capability to produce fruit in a 91 days period, while the same variety cultivated in the greenhouse, produced the fruits 2 month earlier, which is important in off-season production. For the Topai cultivar, which differs from early and middle cultivars in most traits, the phenological stages were longer and the single fruit weight and stalk length were higher comparing to other cultivars. However, in this cultivar, the buds break occurred earlier than other cultivars, although the higher heat requirement from fruit formation to ripening i.e. 55000 CGDH led to later ripening of the crop. Further studies on bioclimatic requirement of other blackberry varieties for proper management decisions and improving the production is recommended.