Morphological integration and genetic variability in Juglans regia L

Italian walnut (Juglans regia L.) is an economically important species in Europe for the value of its wood and fruits. However, little is known about its morphological and genetic variation over the Italian territory. This study presents data on leaf morphology, fruit morphology, and isozyme variation on 21 populations of walnut from Central Italy. A multivariate technique of matrix comparison (Mantel's test) is used to investigate the interrelationships among these three sets of variables. Spatial autocorrelation is used to address the presence of nonrandom distribution of the plants' character values over the territory. Our results show an extreme degree of morphological and genetic variation, but a nonsignificant spatial structure, suggesting phenotypic plasticity in order to produce fitness homeostasis. The matrix of genetic distances is associated with the matrix of leaf morphological distances, and this last one is in turn correlated with the matrix of fruit phenotypic distances. The first and last matrix, however, are uncorrelated, suggesting a chain of causal relationships between the genotype and the two aspects of the phenotype here considered