Intraspecific classification of melons (Cucumis melo L.) in view of their phenotypic and molecular variation

Cucumis melo L. (melon) genotypes differ widely in morphological and biochemical traits. Intraspecific classification of such variability has been difficult, and most taxonomists still rely on the work of Naudin (1859). A collection of 54 accessions representing diverse genotypes from 23 countries was surveyed. Morphological traits related to the vegetative and flowering stages and mature fruit morphology and quality parameters, e.g., taste, aroma, sugar composition and pH, were scored. These were used to construct a 'botanical-morphological' dendrogram that generally reflected the classification of Cucumis melo into several horticultural varieties. DNA polymorphism among the accessions was assessed using the Inter-SSR-PCR and RAPD techniques that detected abundant DNA polymorphism among melon genotypes. Cluster analysis indicated that the largest divergence was between North American and European cantalupensis and inodorus cultivars as one group, and the more 'exotic' varieties: conomon, chito, dudaim, agrestis and momordica, as a second group. The molecular phylogeny agreed, broadly, with the classification of melon into two subspecies, and did not contradict the division into 'horticultural varieties'. It was apparent, however, that the infra-specific division is rather loose, molecular variation being distributed continuously between and within cultivar groups. We suggest that despite the morphological diversity, separation between varietal-groups may be based on a too small number of genes to enable unambiguous infra-specific classification based on DNA diversity.