Genetic structure, differentiation, and slight evidence for no selective neutrality of some SSR markers in populations of Medicago ciliaris (L.) Krock and Medicago intertexta (L.) Mill species

Medicago ciliaris (L.) Krock and Medicago intertexta (L.) Mill are most often found in saline regions and are considered as potential resources for genes related to salinity resistance. To explore the genetic diversity of these two species by mean of nrSSR (simple-sequence repeats) markers, 11 accessions originated from different regions in north of Africa and Middle East were chosen. Ten among 14 markers turned out to be polymorphic and gave 72 alleles. Eight markers were very informative with PIC values > 0.5, and three of them were found to be nonneutral. Allelic richness was limited with an average number of alleles per locus of 2.7. All populations have a significant heterozygous deficit evidenced by both observed heterozygosity rates (null for most populations) and multilocus fixation index estimates. A strong differentiation between populations was highlighted by F-ST (0.805) and G(ST) (0.919) values. Low values of gene flow (0.01-0.38) revealed a very weak gene exchange between populations regardless of the proximity of their sites of origin. The total variability breakdown by analysis of molecular variance (AMOVA test) showed a preponderance of interpopulation component (73%-72%) with respect to intrapopulation one (18%), mainly due to the mating system. Relationship analysis performed by NJ tree representation trends to place M. ciliaris as an ancestor and M. intertexta as a derivative. The two populations from the Sebkha site, characterized by the highest variability and more private alleles, constitute an ideal reservoir of genes for tolerance to salinity. Significant genetic diversity in the two aforementioned species is encouraging for their conservation.

Keywords:

Genetic diversity, genetic structure, M. ciliaris, M. intertexta salinity tolerance, simple-sequence repeats,

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