Population structure and genetic variation in autochthonous globe artichoke germplasm from Sicily Island
Introduction
Globe artichoke (Cynara cardunculus L. var. scolymus L.) is a perennial plant, originating from the Mediterranean Basin, whose capitula (inflorescences), commonly referred to as ‘heads’ or ‘buds’, are consumed worldwide as a fresh, canned or frozen vegetable. Recent studies [1] indicate that southern Italy and Sicily are implicated as the origin of its domestication. Globe artichoke is documented as having been grown in southern Europe since the 15th century but, as reported by De Candolle [2] in the ‘Origin of Cultivated Plants’, Theophrastus (371-266 b.c.) made reference to its cultivation in Sicily. The major use of globe artichoke is for human food, but other potential uses are as a source of fresh biomass as forage for livestock, as a feedstock for the preparation of alcoholic beverages, and as a source of inulin. Furthermore, many references exist in pharmacopoeia describing its health-promoting properties.
Italy is the leading producer (about 50,000 ha) of globe artichoke, followed by Spain and France. In Italy (mainly Apulia, Sicily and Sardinia), artichoke production is an important activity for economic stability and social development and, thanks to its long growth cycle, its cultivation provides employment almost the whole year round. Although to a lesser extent, it is also cultivated in North Africa (Algeria, Egypt, Morocco, Tunisia), the Middle East (Israel, Syria and Turkey), South America (mainly Argentina and Chile), the United States and China [3]. Italy has the richest globe artichoke primary cultivated gene pool, and harbours many distinct clonal varietal groups. Cultivated germplasm has been classified into four main groups, primarily on the basis of capitulum appearance [4], [5], [6]: (I) the Spinosi group, characterised by the presence of long sharp spines on bracts and leaves; (II) the Violetti group, with medium-sized, violet-coloured and less spiny heads; (III) the Romaneschi group, with spherical or sub-spherical non-spiny heads; and (IV) the Catanesi group, with relatively small, elongated and non-spiny heads. Another criteria of classification is based on harvest time: early types can be forced to produce capitula between autumn and spring, if ovoli are watered during summer, while late types produce capitula only during spring and early summer.
In a recent study [7] we analysed, by means of AFLP markers, genetic relatedness among 118 globe artichoke accessions including 89 varietal types. Our results demonstrated that AFLP markers can be useful in evaluating C. cardunculus genetic diversity and in classifying accession to phylogenetic groups based on their genetic similarity values. Furthermore, our results, together with the ones obtained by Sonnante et al. [8] with RAPD fingerprinting, have shown consistent agreement between genotypic and phenotypic classifications based on head characters, indicating that the cultivated morphotypes play an important role in determining variation within the species.
Globe artichoke is an outbreeding species, but is generally propagated via suckers, ovoli (underground dormant shoots), or by division of rooted basal stem portions. Tissue culture procedures are occasionally used for the production of disease-free plantlets, but in vitro micropropagation has yet to be optimised, and the success rate remains low. Seed-propagated cultivars are becoming popular in some parts of the world, but at present very limited results have been obtained into locally adapted Italian germplasm. Notwithstanding the variability present in cultivated Italian germplasm, the number of varietal types with market value is limited to just a few. Moreover, the introduction of both non-autochthonous and seed-propagated varieties is leading to a progressive erosion of local germplasm.
The objectives of the present research were to investigate: (i) the level of genetic diversity in seven populations of the two Sicilian globe artichoke varietal types ‘Violetto di Sicilia’ and ‘Spinoso di Palermo’; (ii) how genetic diversity is distributed within and among these populations; (iii) the frequency within each population of specific and/or locally common alleles. Our intention is to help identify strategies both for the sustainable management of the genetic resources of Sicilian globe artichoke, and for the development of future breeding programmes.
Section snippets
Plant material and DNA extraction
Of the seven Sicilian populations of globe artichoke identified, four [Ramacca loc. Margherito (RAM), Rosolini (ROS), Niscemi (NIS), and Caltagirone (CAL)] belonged to the varietal type ‘Violetto di Sicilia’ (VS), and three [Buonfornello (BUO), Caccamo (CAC) and Licata (LIC)] to ‘Spinoso di Palermo’ (SP) (Fig. 1). The stands (5000–20,000 individuals per population) grow at altitudes from 15 to 150 m a.s.l., and were considered representative of the overall cultivation area. The distance between
AFLP genetic variability
Table 1 summarizes the statistical parameters for each population. The five PCs used allowed the scoring of 169 polymorphic bands; the highest number of polymorphic bands was generated by E38/M47 (46 polymorphisms, Table 2). The number of polymorphic bands as well as the average number of observed alleles (no) and genetic diversity (H′) were significantly higher for the VS populations (105, 1.62 and 0.065, respectively) than for the SP ones (81, 1.48 and 0.054, respectively), while the average
Discussion
The artichoke varietal types currently grown in Italy are commonly classified by capitulum morphology (specifically: size, shape, pigmentation, and presence/absence of spines) and/or by harvest time. Little is known about the process of its domestication and subsequent diversification, but a number of lines of evidence [7], [22], [23], [24] point to its evolution from the wild cardoon. The significant genetic differentiation between spiny and non-spiny types [7] is suggestive that the two forms
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