Variability and grouping of northwestern Spanish chestnut cultivars. I. Morphological traits

Abstract

Different chestnut (Castanea sativa Mill.) cultivars are at present grown in the region of Galicia, northwestern Spain, but no distinguishing traits among cultivars have been defined so far. The objectives of this research were to 1) describe the intra and intercultivar variability of chestnut cultivars; 2) define primary morphological traits to be useful for a simple morphological classification system of the cultivars; and 3) study the association between some environmental variables and the morphological traits. Seventeen morphological traits in a sample of 373 trees belonging to 82 local cultivars of chestnut were studied by methods of numerical taxonomy, principal component and cluster analysis. These traits were selected from 135 previously studied as having possible discriminating taxonomic value. Significant variability among cultivars and among trees within cultivars was found for most of the traits. The trees were grouped according to the degree of dissimilarity on the basis of the Mahalanobis generalized distance. Most of the clones collected under a specific cultivar name were included within the same cluster group enabling us to classify 53 of the cultivars studied. A hierarchical classification system that identifies eigth cultivar groups is proposed based on four discriminating levels: nut size, fruit shape, male flow type and length of burr spines. Most of the correlations between the environmental variables and the morphological traits were no significant or had a low value. The lack of correlation between the environmental variables and nut size indicates that this important trait is under strong genetic control, it is not influenced by environmental conditions and it is consistent throughout the area sampled.