Cytogenetic characterization of cultivated globe artichoke (Cynara cardunculus var. scolymus) and cardoon (C. cardunculus var. altilis )

Cynara cardunculus L. is a typical Mediterranean species comprising two important cultivated types, the globe arichoke (Cynara cardunculus var. scolymus) which is grown for its edible heads and the cultivated or leafy cardoon (C. cardunculus var. altilis) appreciated for its fleshy steams and leaf stalks. It includes also a third form, the wild cardoon (C. cardunculus var. sylvestris) which is considered the ancestor of the cultivated forms. Despite progress in the evolutionary field, advanced chromosome studies on C. cardunculus are almost nonexistent. The objective of this study was to fill in this gap by providing a refined cytogenetic characterization of the cultivated scolymus and altilis varieties. The karyomorphological analysis showed that artichoke and cardoon share an identical karyotype. All chromosomes are metacentric but are markedly differentiated with respect to their length, therefore they could be separated into three groups of different size: large (L), medium (M) and small (S). As a first step towards the physical mapping of artichoke and cardoon chromosomes, the FISH technique was applied to localize the position of 18S-5.8S-25S rRNA genes (45S rDNA). The fluorescent signals obtained by the FISH experiments constituted reliable landmarks for the identification of two pairs of M chromosomes and two pairs of S chromosomes. The overall results represent a significant advance in C. cardunculus cytogenetics and suggest further investigation of the wild sylvestris variety in order to acquire more exhaustive information on the evolutionary pathway of the species.