Genetic variation at early ages for several traits of interest for timber-production breeding of Juglans regia

Several traits of common walnut (Juglans regia L.) were assessed during the first three growing seasons in a progeny test of 43 open-pollinated families at two sites in northwestern Spain. Variance components, heritabilities and correlations between traits were calculated for all characteristics measured. Significant differences were found among families with regard to growth, phenology, frost damage, number of apical branches, and Phytophthora cinnamomi Rands damage, but not for growth-habit traits (number of branches, stem form, and apical dominance). Heritabilities were moderate for total height (h^2i => 0.32; h^2f => 0.63) and late-spring frost damage (h^2i = 0.29; h^2f = 0.57), high for resistance to P. cinnamomi (h^2i = 0.76; h^2f = 0.85), and low for phenology (h2i = 0.15; h^2f = 0.39 for bud burst, and h^2i = 0.14-0.36; h^2f= 0.44-0.70 for leaf fall) and root-collar diameter (h^2i = 0.18-0.29; h^2f = 0.41-0.58). High age-age correlations were found for growth and phenology traits during the first three growing seasons. Some interesting correlations were also found between several of the traits studied. The families whose buds burst the earliest had more late-spring frost damage and, consequently, more apical branches (i.e., branches near the apical bud). Furthermore, the greater the resistance to P. cinnamomi and frost damage, the taller the families.