Comparison between phenetic characterisation using RAPD and ISSR markers and phenotypic data of cultivated chestnut (Castanea sativa Mill.)

Patterns of phenotypic and phenetic variability in six Portuguese cultivars of chestnut (Castanea sativa Mill.) are evaluated. Morphological characterisation was based on the quantification of seventeen traits. Variance analysis showed significant differences among cultivars, and cultivar x year for all the traits studied, and trees within cultivars showed also some significant differences for some of the morphological variables. A significant correlation was obtained between length of the leaf blade and the percentage of unisexual and androgynic inflorescence with the effective thermal index, accumulated rainfall from April to October and from July to October, or the accumulated temperature below seven during the dormant period. Principal Component and cluster analysis were performed to group the cultivars, according to their similarity coefficients. For molecular characterisation, 125 RAPD and 157 ISSR polymorphic markers were amplified using 28 and 7 primers respectively. High level of congruence among the two marker systems (r = 90.5%) was obtained from comparison of phenetic similarities based on the percentage of shared fragments. ISSR markers revealed important advantages over RAPDs, due to a high effective multiplex ratio (12.5 for ISSR compared with 2.2 for RAPD analysis) and reproducibility. Although morphological and molecular results are comparable, slight differences are showed in cluster analysis UPGMA dendrograms. Molecular analysis explained homonym situations among 'Martainha' and 'Longal' cultivars in Portugal.