Genetic structure of island populations of wild cardoon [Cynara cardunculus L. var. sylvestris (Lamk) Fiori] detected by AFLPs and SSRs
Introduction
Wild cardoon [Cynara cardunculus L. var. sylvestris (Lamk) Fiori] is a non-domesticated robust perennial plant, characterized by its rosette of large spiny leaves, branched flowering stems and blue-violet flowers. It belongs to the family of Asteraceae, tribe Cynareae and is native to the Mediterranean basin, where it colonizes dry and undisturbed areas. Molecular [1], [2], [3], [4], as well as cytogenetic and isozyme [5] studies indicate that the species is the ancestor of the cultivated forms, globe artichoke (C. cardunculus var. scolymus L.) and cardoon [C. cardunculus. var. altilis (DC)], since they are fully cross-compatible and their F1 hybrids are fully fertile [6].
Wild cardoon is allogamous and is propagated by seeds (achenes). The majority of seed is shed close to the parent plant, and germinates after the first autumn rains, although germination may occur all year round under favourable conditions; the growth period spans September (emergence) to July (achene maturity), and flowers are usually produced by 2-year-old plants. Like globe artichoke, the fleshy heads (immature flowers) as well as the petioles and roots, if properly prepared, are edible. Previous studies have shown that wild cardoon is also a promising source of seed oil, both with respect to quality and quantity, and the residue flour after extraction is usable as a component of animal feed. Seed yield is in the region of 2.0 tonnes/ha (at 5% (w/v) moisture), of which about 25% is oil [7]. The high proportion of oleic and linoleic acids, in a balanced ratio, and the low amount of free acids, peroxides, saturated and linoleic acids are responsible for its good alimentary quality. In addition, a favourable α-tocopherol content provides good stability against oxidation [8]. Wild cardoon could also be exploited for the production of lignocellulosic biomass for energy or paper pulp [9], as the biomass yield is up to 19.0 tonnes/ha dry matter [7], [10]. Furthermore, wild and cultivated forms of Cynara cardunculus are a source of biopharmaceuticals [11], [12], [13], [14]. The roots contents include inulin, a known improver of human intestinal flora, while the leaves are a source of antioxidant compounds, such as luteolin and di-caffeoylquinic acids, which (i) protect proteins, lipids and DNA from oxidative damage caused by free radicals [15], [16], [17], (ii) inhibit cholesterol biosynthesis and contribute to the prevention of arteriosclerosis and other vascular disorders [16], [18], [19], [20], (iii) inhibit HIV integrase, a key player in HIV replication and its insertion into host DNA [21], [22], and (iv) possess antibacterial activity [23]. Little is known of the extent or pattern of genetic variation in natural populations of wild cardoon, particularly with respect to variation in the chemical profiles of leaf extracts. Furthermore, there has been no attempt as yet to genetically improve the taxa, with a viewing to increasing seed oil or biomass yield.
DNA markers well suited to assess genetic diversity. Their advantages are that most exhibit no plasticity, that they are unlikely to be similar because of convergent evolution, and they can generate information at many different loci [24]. The two most widely applied marker systems are amplified fragment length polymorphism (AFLP) [25] and microsatellites (simple sequence repeats, SSR) [26]. Some SSR assays have been developed recently for Cynara cardunculus [4], [27], [28]. Owing to their co-dominant inheritance, SSRs detect multiple alleles at a given locus while AFLP, being dominant, detect multiple loci distributed throughout the genome. Hence different data analysis approaches are needed to obtain comparable statistics [24], [29], [30]. However, comparative studies over a wide range of species have generally revealed a good congruence between genetic parameters revealed by these two marker systems [24], [31], [32], [33].
The objectives of the present study were: (i) to investigate the level of AFLP and SSR variation in seven populations of wild cardoon, (ii) to quantify the genetic diversity within and between wild cardoon populations, (iii) to compare the informativeness of the AFLP and SSR assays employed at the level of populations and individuals, and (iv) to identify approaches towards a rational sampling strategy programme in wild cardoon.
Section snippets
Plant material and DNA extraction
Four populations of wild cardoon were identified in Sicily [Roccella (SIC-ROC), Bronte (SIC-BRO), Piano Tavola (SIC-TAV), and Palazzolo (SIC-PAL)], and three in Sardinia [Sassari (SAR-SAS), Nuoro (SAR-NUO) and Oristano (SAR-ORI)] (Fig. 1). The sites vary in altitude from 50 to 700 m a.s.l., and each covers an area of ca. 1–2 ha. From each population, leaf material from 30 randomly chosen individuals was collected and used as a source of genomic DNA, which was extracted following methods described
Microsatellite genetic diversity and HW equilibrium
The statistical parameters relating to the SSR loci for each population are reported in Table 1. The five SSR loci detected 67 alleles across the 210 individuals. The number of alleles per locus ranged from 9 (CMAL-108) to 20 (CMAL-06) with a mean of 13.4. Within each population, the allele frequency ranged between 0.017 and 1, with an overall mean value of 0.170. The average number of observed alleles (no) was 12.0 and 8.4, respectively, for the Sicilian and Sardinian, populations; the average
Discussion
This report represents the first analysis of SSR-based genetic differentiation between and within populations of wild cardoon. In a previous work Raccuia et al. [56] by means of AFLP markers analysed genetic variation in six Sicilian populations, however only four plants per population were sampled and thus their data do not appear comparable. As the species is outcrossing and seed-propagated, it is expected to display high levels of heterozygosity. Wild cardoon grows in dense stands and can
Acknowledgements
We thank Dr. L. Barchi for technical assistance and Dr. A. Rottenberg for the critical reading of the manuscript.
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2012, Comptes Rendus - BiologiesCitation Excerpt :The value FST = 0.1891 determines that a majority (81.09%) of the total genetic variation is explained by the intrapopulation genetic diversity and 18.91% of this variability is attributed to the differences between the studied populations. This level of genetic differentiation is similar to the levels cited in other studies of Asteraceae populations: 14.1% for the island wild cardoon populations from Italy [4] and 17.9% for the populations of Ligularia sibirica [34]. FST is calculated between the studied populations; the parameter of genetic differentiation – (FST = 0.09) between Twirif and Enfidha, (FST = 0.08) between Bouficha and Bahra, between Bouficha and Twirif, between Bahra and Twirif, between Bahra and Zriba and between Twirif and Zriba, (FST = 0.07) between Bouficha and Wad mliz, between Bahra and Enfidha, between Wad mliz and Twirif, between Wad mliz and Zriba and (FST = 0.06) between Bahra and Wad mliz, between Bouficha and Zriba, between Bouficha and Enfidha and between Wad mliz and Enfidha – reflects the lack of geographical and genetic structure between these populations that appear homogeneous.