Medicago polymorpha is a herbaceous legume that can be a useful pasture plant, in particular, in regions with a Mediterranean climate. The genetic variation in 120 lines of M. polymorpha sampled from five regions in Tunisia was characterized on the basis of 16 morpho-phenological characters. Results from analysis of variance (ANOVA) showed that differences among populations and lines existed for all traits, with population explaining the greatest variation for measured traits. The populations of Enfidha and Soliman were the earliest flowering, while those of El Kef, Bulla Regia and Mateur were the latest. El Kef and Mateur exhibited the highest aerial dry weight while the lowest value was found for Soliman. Moderate to lower levels of heritability (H²) were registered for investigated traits. There was no significant association between pairwise population differentiation (Q ST) and geographical distances. Studied lines were clustered into three groups with 59 for the first group, 34 for the second group, and 27 lines for the third group. The lines of the first two groups showed the largest length of stems while those of the second group had the highest number of leaves. The variation of quantitative traits among populations was influenced by the altitude, temperature and relative humidity. Overall, the high levels of within population variation and the lack of correlation between population differentiation and geographical distances suggest a potentially important rate of long-distance seed dispersal and confirm the role played by natural selection in the population structure of Tunisian populations of M. polymorpha.

Spring black stem and leaf spot, caused by <i>Phoma medicaginis</i>, is an issue in annual Medicago species. Therefore, in this study, we analyzed the response to <i>P. medicaginis</i> infection in a collection of 46 lines of three annual Medicago species (<i>M. truncatula</i>, <i>M. ciliaris</i>, and <i>M. polymorpha</i>) showing different geographic distribution in Tunisia. The reaction in the host to the disease is explained by the effects based on plant species, lines nested within species, treatment, the interaction of species × treatment, and the interaction of lines nested within species × treatment. <i>Medicago ciliaris</i> was the least affected for aerial growth under infection. Furthermore, the largest variation within species was found for <i>M. truncatula</i> under both conditions. Principal component analysis and hierarchical classification showed that <i>M. ciliaris</i> lines formed a separate group under control treatment and <i>P. medicaginis</i> infection and they are the most vigorous in growth. These results indicate that <i>M. ciliaris</i> is the least susceptible in response to <i>P. medicaginis</i> infection among the three Medicago species investigated here, which can be used as a good candidate in crop rotation to reduce disease pressure in the field and as a source of <i>P. medicaginis</i> resistance for the improvement of forage legumes.

Medicago polymorpha L. is a herbaceous legume that can be a useful pasture crop, especially in Mediterranean climates. This study aimed to analyze the genetic variation in five populations of M. polymorpha collected from different ecogeographic regions in Tunisia using eight SSR markers. The transferability of 112 SSR markers distributed on the eight chromosomes of M. truncatula Gaertn. showed that 50 SSR markers could be amplified in M. polymorpha. Among these 50 SSR markers, eight (8) markers were polymorphous. A high level of polymorphism (126 polymorphic alleles with an average of 5.3 alleles per locus) and a moderate level of genetic diversity were found in all the studied populations, with observed and expected heterozygosities averaging between 0 and 0.69, respectively. Results from analysis of molecular variance (AMOVA) revealed that the most variation was found within populations (76%). Moderate levels of population differentiation (FST = 0.12 to 0.19) accompanied by a high rate of gene flow between populations (Nm = 1.08 to 1.83) were recorded. This molecular differentiation (FST) was not dependent on geographical distances (r = 0.395, p = 0.524), suggesting that studied populations are not geographically isolated. Our results showed that studied populations were clustered into three groups. A first group is formed by the populations of El Kef (TNP7) and Bulla Regia (TNP9), a second group of Enfidha (TNP1) and a third group of Soliman (TNP8) and Mateur (TNP11). Results obtained in our study could be helpful for breeders considering introduction of some lines of this species into M. polymorpha breeding programs.

Soil salinity is one of the most serious environmental factors affecting crop productivity around the world. We used a morpho-physiological approach to investigate the salt responses of four Tunisian natural populations of Medicago ciliaris. Forty-six lines of M. ciliaris were grown under a control treatment and 100 mM NaCl. We measured 11 quantitative traits of shoot and root growth during harvest. An analysis of variance showed that the variations in salt response can be explained by the effects of the population, line, treatment, and interactions between the population and treatment and the line and treatment. Most of the measured traits showed significant differences between the studied populations under the control treatment and salt stress. High to moderate broad-sense heritabilities (H2) were noted for most of the parameters under the control treatment and salt stress, implying that salt tolerance is highly heritable. Most correlations between the measured traits under the two treatments were positive, of which the strongest correlations were recorded between characteristics related to development. The 46 studied lines formed three groups in both conditions, while their genetic structure was dependent on the treatment factor. The results from this study can provide a basis for identifying and breeding salt-tolerant lines of M. ciliaris.