Genotypic differences in branching pattern and fruiting habit in common walnut (Juglans regia L.)

Architectural analysis of 840 Slovenian walnut (Juglans regia L.) genotypes was performed to determine the most typical and frequent morphological types and to evaluate their vegetative and generative potential. Four branching and fruiting patterns (I-IV) were detected. A 3-year-old fruiting branch, consisting of a 3-year-old shoot plus corresponding 2-year-old and 1-year-old shoots, was used as a structural unit for quantitative analysis. In the intermediate fruit-bearing types with mesotonic and acrotonic branching pattern (types II and III), the total lengths of 3-, 2- and 1-year-old shoots were 385 and 380 cm, respectively, compared with 275 and 253 cm in the terminal and lateral-fruiting types (types I and IV). In type I, 1-year-old shoots had significantly fewer nodes than in other types. In addition, they had a thinner basal diameter than types III and IV, and their angles were the most erect (39 degrees ). Only 0.4 out of 3.6 1-year-old shoots were flowering with one mixed bud with 1.9 female flowers. In type IV, 2-year-old shoots had significantly more nodes and a larger basal diameter than other types. One-year-old shoots in type IV are thicker than those in other types. Ratios between the number of flowering and the total number of 1-year-old shoots were 0.7 in type IV, 0.6 in type III, 0.5 in type II and 0.1 in type I. On 1-year-old shoots in type IV, 1.7 mixed buds with a mean of three female inflorescences per bud were counted. Consequently, the generative potential is highest in type IV and lowest in type I. In types II and III, growth and the ability to bear fruits are more balanced.