Genetics of frost hardiness in Juglans regia L. and relationship with growth and phenology

The growing interest in broadleaf timber plantations in the Mediterranean area has promoted several studies focusing on the identification and characterization of variability sources in main timber-producing species. J. regia is one of these species, well-adapted to this area, but with freezing, damages registrations. Breeding focused on productive traits should include knowledge of adaptation, required to obtain a good selection capable of producing a suitable turnover in timber plantations. In this study, the features evaluated were autumn and winter frost hardiness and some vegetative traits on 22 half-sib J. regia progenies. Budsticks were exposed to sub-zero temperatures in a controlled chamber and using measurements of relative electrolyte content, the LT50 values (°C) were calculated by each individual. The study was carried out on seven-year-old progenies. The familiar heritability of autumn frost hardiness was 0.68, and on winter, it was 0.77. The autumn frost behaviour correlated genetically with the length of the growing season (0.574 ± 0.351), and both autumn and winter frost hardiness correlated inversely with secondary annual growth measured at breast height (−0.654 ± 0.259 and −0.740 ± 0.227, respectively). These results pointed that growth could therefore be improved without increasing the frost vulnerability. This should be important for growers, particularly under climate change conditions.