Biochemical changes in terminal buds of three different walnut (Juglans regia L.) genotypes during dormancy break

To the better management of frostbite problem in fruit crops, evaluation of biochemical changes in buds during dormancy break is a key factor. In this study biochemical changes in terminal buds of three different walnut genotypes (early-season, mid-season, and late-season), was investigated during winter dormancy release time. Terminal bud samples were taken from the genotypes in two different times in winter (1st and 20th of March). Variables such as; bud soluble sugars, starch, proline, chlorophyll, total phenolic and protein content as well as catalase (CAT) and guaiacol peroxidase (GPO) enzymes activities were assessed. Analysis of variance ANOVA) revealed significant differences (p ≤ 0.05) for the measured variables and sampling times among the genotypes. The results indicated that the late growth genotype had the highest content of soluble sugars and proline, and the lowest amount of starch and protein (p ≤ 0.05) in comparison with early and mid-season growth genotypes. Different enzymes activities were observed in terminal buds among the genotypes. As sampling time delaying, the content of chlorophyll, CAT and GPO enzymes activity increased, while a decrease in proline and total phenol was observed. The results of this study can be considered to a better understanding of the primary mechanisms of bud dormancy break in walnut to reduce the late spring frost damage problem as well as for using in breeding programs.