Inter- and Intraspecific Variation in California Black Walnuts

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Abstract
Genetic variation in vigor, phenology, and branching in juvenile seedlings of Juglans californica and J. hindsii was investigated. Significant differences between species were detected in traits that reflect vigor (height, diameter, volume), in phenological traits (dates of leafing out and leaf drop), and in branching. J. californica was generally more vigorous, more branched, leafed out earlier, and dropped leaves later than J. hindsii. When species were analyzed separately, seed source was a highly significant source of variation for phenological traits and branching in J. hindsii. Upper estimates of heritability for phenological traits ranged from 0.47 to 0.88. The results of this study suggest that J. hindsii may have had a history of differentiation and adaptation to latitude, elevation, or other climatic characters. Conservation of germplasm resources in J. hindsii will be essential to maintain the purity of the species and to provide resources for studying the species and breeding rootstock for J. regia, the Persian walnut.

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