Genotype and environment: two factors related to autumn cold hardiness on Persian walnut (Juglans regia L.)

Abstract

J. regia timber is appreciated for high-value wood products. In new plantations, biotic or abiotic events which could affect wood quality should be monitored. Autumn frosts could affect annual shoot development, with consequent loss of timber value or even tree death. In southern Europe, climate change forecasts include erratic and severe autumn frost events. The relationship between genotype and environment regarding susceptibility to autumn frost damage was examined in four provenances of Juglans regia L., planted at two ecologically different sites, one subject to Mediterranean and the other Atlantic weather conditions. Annual budsticks from eight trees per provenance were collected in November 2010 from each site. The samples were then submitted to freeze–thaw cycles down to −8, −13 and −18 °C, plus a control treatment (keeping samples at 5 °C). Damage to the stem was assessed using the index of freezing injury calculated from relative electrolyte leakage at each temperature considered. Frost damage to stem, apical and lateral buds was recorded by visual scoring. Differences in cold acclimation between sites were detected, with provenances exhibiting differences on senescence. A ‘provenance × site’ interaction was found in some of the analyses, but the same ranking of susceptibility was detected for all provenances at both sites and in all the tissues analysed. The differences between provenances could be related to their geographical origins, where an altitude gradient was observed. The genetic component was important in the expression of autumn cold hardiness and, together with productive traits, should be considered in new afforestation projects.