Adaptive diversity in Castanea sativa Mill. half-sib progenies in response to drought stress

► Progenies of Spanish chestnut cultivars were assessed under drought stress trials. ► Water potential and key morphological and growth traits varied between progenies in response to drought. ► A variation gradient, reflected in growth and morphological traits, was found between the two origins of variability due to genetic differentiation. Variation patterns in phenotypic expression after cultivation in two water regimes: 50% and 90% substrate saturation were studied in progenies of chestnut (Castanea sativa Mill.) cultivars originating from two main origins in the Iberian Peninsula: North (specifically from Asturias and Galicia) and Central Iberian Peninsula (specifically from the Canary Islands and Andalusia in Southern Spain related to this gene pool). The restricted water supply reduced the water potential of all the families as well as their growth, both in terms of height and weight. Root development increased whilst leaf area decreased as a result of reduction in number and surface area of individual leaves as well as sprouting rather than through defoliation. Drought stress also modified the morphology of the leaves and the relationships indicating the rate of relative development of the leaves compared to the rest of the plant. A correlation with the minimum summer rainfall in the regions of provenance was observed for several traits. The phenotypic variation observed was greater than expected from progenies of selected fruit cultivars. The results of this study show that (i) phenotypic variation exists between the two origins of variability corresponding to the two identified gene pools; (ii) the Northern group might be considered more tolerant to drought stress when considering plantlets’ ability to recover water potential, though important phenotypic plasticity was found in both origins of variability; and (iii) the pattern of variation found in some physiological and morphological traits suggests that Spanish chestnut stands have great potential to respond to the expected increase in drought in the Iberian Peninsula over the present century.