Nut and kernel growth and shell hardening in eighteen hazelnut cultivars (Corylus avellana L.)

Growth and development of nuts and kernels were measured in 18 hazelnut (Corylus avellana L.) cultivars from cluster appearance until nut maturity and drop. At harvest, shell thickness and force to penetrate the shell were determined and related to the incidence of nut weevil damage. The force to penetrate the shells started to increase when nuts reached 80-90% of their final size, and continued until kernel full size. During nut growth, shell hardness and kernel size were highly correlated (R-2 = 0.921). At maturity, values of force ranged from 46.7 to 185.7 N. Values of nut weevil damage ranged from 0.6 to 24.4%. At harvest, the force to penetrate the shells was highly correlated with the shell thickness (r = 0.945) and negatively correlated with the nut weevil damage (r = -0.564). Late onset of nut development was associated with a high percentage of nut weevil damage (R = 0.638). These information can be used to model nut development and provide important tools for planning orchard management activities.