Genetic diversity and population structure of Cynara cardunculus L. in southern Portugal

Abstract

Cynara cardunculus L. is a cardoon species native to the Mediterranean region, which is composed of three botanical taxa, each having distinct biological characteristics. The aim of this study was to examine wild populations of C. cardunculus established in Portugal, in order to determine their genetic diversity, geographic distribution, and population structure. Based on SSR markers, 121 individuals of C. cardunculus from 17 wild populations of the Portuguese Alentejo region were identified and analysed. Ten SSRs were found to be efficient markers in the genetic diversity analysis. The total number of alleles ranged from 9 to 17 per locus. The expected and observed means in heterozygosity, by population analysed, were 0.591 and 0.577, respectively. The wild population exhibited a high level of genetic diversity at the species level. The highest proportion of genetic variation was identified within a geographic group, while variation was lower among groups. Geographic areas having highest genetic diversity were identified in Alvito, Herdade da Abóboda, Herdade da Revilheira and Herdade de São Romão populations. Moreover, significant genetic differentiation existed between wild populations from North-Alentejo geographic locations (Arraiolos, Évora, Monte da Chaminé) and Centro Hortofrutícola, compared with other populations. This study reports genetic diversity among a representative number of wild populations and genotypes of C. cardunculus from Portugal. These results will provide valuable information towards future management of C. cardunculus germplasm.

Fig 1. Maps indicating geographic locations and distribution of the wild populations of Cynara cardunculus, sampled in Portugal.

Fig 2. Principal coordinate analysis of Nei’s genetic distance for the 17 geographic populations of Cynara cardunculus.

Fig 3. Structure analysis based on 121 genotypes of Cynara cardunculus.

Genetic clusters inferred from the population structure analysis at K = 2 (A), 3 (B) and 8 (C), are represented by individual colors. Each sample (represented by a vertical bar) is partitioned into colored segments representing the estimated membership coefficients (q values). Genotypes names (geographic location followed by genotype number) are indicated on the x axis. Bar colors indicate the groups identified through the STRUCTURE program.

Fig 4. NJ phylogenetic tree showing affiliations of the Cynara cardunculus populations based on genetic dissimilarity of SSR microsatellite analyses.

Geographic origin of populations is identified by a colour (see Table 1 for abbreviations of geographic populations).