Before the recent advances in molecular biology and sequencing techniques enabled a deep knowledge of the complete nucleotide sequence of many plant genomes, cytological and karyological studies have provided the first information concerning the genome organization of living beings. As stated by Figueroa and Bass (2010), plant cytogeneticists were among the earliest researchers who started to visualize genomes nearly a century before the first plant genome was sequenced (The Arabidopsis genome initiative 2000). In spite of the high development of next-generation sequencing approach and of the dramatic increase in available data regarding sequenced genomes, the cytological analysis of cell nucleus content remains a valuable tool for evolutionary studies and for structural and functional genomic research. Since Wilhelm Gottfried von Waldeyer-Hartz coined the term chromosome in 1888, many cytological techniques have been developed to disclose nucleus content and to allow a detailed description of the chromosome complement of plant species. Recently, some of these techniques have been applied to the cytological analysis and the molecular cytogenetic characterization of Cynara cardunculus complement, a traditional vegetable crop of the Mediterranean basin. The DNA content and a detailed karyotype of the two cultivated botanical varieties C. cardunculus var. altilis DC (cultivated cardoon) and C. cardunculus L. var. scolymus L. (globe artichoke) have been reported (Khaldi et al. 2014; Falistocco 2016; Giorgi et al. 2016). In this chapter, some of the used methodological approaches and the main results obtained by different authors will be discussed.

Traditionally globe artichoke and leafy cardoon have been cultivated for use as vegetables but these crops are now finding multiple new roles in applications ranging from paper production to cheese preparation and biofuel use, with interest in their functional food potential. So far, their chromosome complements have been poorly investigated and a well-defined karyotype was not available. In this paper, a detailed karyo-morphological analysis and molecular cytogenetic studies were conducted on globe artichoke (Cynara cardunculus Linnaeus, 1753 var. scolymus Fiori, 1904) and leafy cardoon (C. cardunculus Linneaus, 1753 var. altilis De Candolle, 1838). Fluorescent In Situ Hybridization In Suspension (FISHIS) was applied to nuclei suspensions as a fast method for screening of labelling probes, before metaphase spread hybridization. Classic Fluorescent In Situ Hybridization (FISH) on slide, using repetitive telomeric and ribosomal sequences and Simple Sequence Repeats (SSRs) oligonucleotide as probes, identified homologous chromosome relationships and allowed development of molecular karyotypes for both varieties. The close phylogenetic relationship between globe artichoke and cardoon was supported by the very similar karyotypes but clear chromosomal structural variation was detected. In the light of the recent release of the globe artichoke genome sequencing, these results are relevant for future anchoring of the pseudomolecule sequence assemblies to specific chromosomes. In addition, the DNA content of the two crops has been determined by flow cytometry and a fast method for standard FISH on slide and methodological improvements for nuclei isolation are described.

In order to develop a non-chemical method such as grafting effective against well-known artichoke soil borne diseases, an anatomical study of union formation in artichoke grafted onto selected wild and cultivated cardoon rootstocks, both resistant to Verticillium wilt, was performed. The cardoon accessions Belgio (cultivated cardoon) and Sardo (wild cardoon) were selected as rootstocks for grafting combinations with the artichoke cv. Romolo. Grafting experiments were carried out in the autumn and spring. The anatomical investigation of grafting union formation was conducted by scanning electron microscopy (SEM) on the grafting portions at the 3rd, 6th, 10th, 12th day after grafting. For the autumn experiment only, SEM analysis was also performed at 30 d after grafting. A high affinity between artichoke scion and cardoon rootstocks was observed, with some genotype differences in healing time between the two bionts. SEM images of scion/rootstock longitudinal sections revealed the appearance of many interconnecting structures between the two grafting components just 3d after grafting, followed by a vascular rearrangement and a callus development during graft union formation. De novo formation of many plasmodesmata between scion and rootstock confirmed their high compatibility, particularly in the globe artichoke/wild cardoon combination. Moreover, the duration of the early-stage grafting process could be influenced not only by the scion/rootstock compatibility, but also by the seasonal conditions, being favored by lower temperatures and a reduced light/dark photoperiod.