This is a large-scale molecular study based on simple sequence repeat (SSR) loci of the diversification process in chestnut cultivars from Portugal and Spain, from the northern Iberian Peninsula to the Canary Islands and the Azores. A total of 593 grafted chestnut trees (Castanea sativa Mill.) were analysed with 10 SSRs: 292 from Portugal and 301 from Spain. Some of the trees studied were more than 300 years old. Accessions were analysed using a model-based Bayesian procedure to assess the geographical structure and to assign individuals to reconstructed populations based on the SSR genotypes. We found 356 different genotypes with a mean value of clonality of 33% owing to grafting. Mutations accounted for 6%, with hybridization being the main diversification process that can explain the great diversity found. Ten main cultivar groups were detected: four in northern Spain, five in the centre of the Iberian Peninsula, and one in southern Spain related to the centre of the Iberian Peninsula. This work demonstrated that cultivar origin and the diversification process was a combination of clonal propagation of selected seedlings, hybridization, and mutations, which allowed high levels of diversity to be maintained with respect to selected clones for fruit production. Furthermore, seedlings and graft sticks facilitated the transport to new destinations in the colonization process, transporting sometimes more than 3000 km if we consider the Azores and the Canary Islands.

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.

ISHS VII International Symposium on Vaccinium Culture BLUEBERRY CULTURE BOTH IN POTS AND UNDER ITALIAN-TYPE TUNNELS