Two-hundred and ninety-five trees sampled from seventy-five local chestnut (Castanea sativa Mill.) cultivars in northwestern Spain, which had been previously studied morphologically, were further analyzed for five isoenzyme systems, encoded by seven loci. Objectives of this study were to 1) describe the intracultivar and intercultivar variability by isoenzyme analysis and to compare it with the morphological variation and 2) establish a classification of the cultivars and to discuss its relation to the morphological classification. Variability within and among cultivars was detected, confirming the previous morphological results. The level of the observed heterozygosity in this Spanish population was higher than expected and also higher than that found in other European populations. Because of the great diversity discovered, this material seems to be worthy for introducing and maintaining in a germplasm bank. Nineteen main clusters were identified for the twenty-three most widely distributed cultivars. On the average, 61% of the trees belonging to a specific cultivar was included in the same cluster. The remaining 39% was scattered in other clusters, which indicates intracultivar variability. Therefore there is opportunity for selection within cultivars. Two clusters included three important cultivars each. This suggests possible synonymies. No correlation between morphological traits and the isoenzymic alleles was detected. The isoenzyme technique identified a higher number of cultivars increasing the information obtained with morphological traits. Correlations between the frequency of some of the alleles and the altitude and other environmental variables suggest that selection of the best adapted genotypes has occurred.
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