Search

Total phenol content, antioxidant and allelopathic properties of roots, steems and leaves extracts of Tunisian endemic T. numidicus were studied. Three solvent systems with varying polarities (petroleum ether, ethyl acetate and methanol) were used. The highest amounts of polyphenols (98.66 ± 3.17 mg EAG/g DW), flavonoids (54.28 ± 1.6 mg RE/g DW), flavonols (27.23 ± 1.71 mg RE/g DW) and proanthocyanidins (5.12 ± 0.8 μg cyanidin chloride/g DW) were shown by the polar subfraction of the leaf methanolic extracts. The efficiency of the solvents used to extract phenols from the three organs varied considerably. The level of antioxidant activity estimated by DPPH and ABTS test systems was high for leaf (IC 50 = 11.06 ± 0.33 μg/ml; 235.46 ± 2.14 μg TE/mg DW) and stems (IC 50 = 15.29 ± 0.9 μg/ml; 233.75 ± 1.2 μg TE/mg DW) methanolic extracts. A significant correlation between radical-scavenging capacities of extracts with total phenolic compound content was observed. The results also indicate that the root extracts inhibited the shoot and root growth of Medicago sativa and Triticum æstivum seedlings. Thus, the T. numidicus extracts may be used as a natural herbicide. [ABSTRACT FROM AUTHOR]

In Tunisia,Thymus algeriensisoccurs in small scattered populations decreasing progressively in size. However, no conservation programs are attempted to promote and preserve the potential value of this resource. In this work, we assessed the genetic diversity of 21 populations ofT. algeriensiscollected from different geographical regions using nine isozyme systems. Fourteen polymorphic loci were detected and several ones were rare alleles according to population level. The species showed a high genetic diversity within populations (Ap = 2.25;P% = 75.71%;Ho = 0.151). A relatively high level of differentiation (FST = 0.146) associated with a restricted gene flow among populations (Nm = 2.385) was revealed. A significant population differentiation (0.055 < FST < 0.183) was observed within ecological groups. The relationship betweenFSTand geographic distance matrices was not significant, indicating that the genetic structure among populations is more linked to fragmentation of populations. Nei's genetic distances (D) among pairs of populations were low (0.005 < D < 0.126). The substantial differentiation between populations and their high genetic similarity suggest their recent divergence as a result of habitat fragmentation and isolation of populations. UPGMA clustering showed four aggregates according to their geographic and bioclimatic originality. Theex situconservation should be based on sampling seeds within rather than among populations. [ABSTRACT FROM AUTHOR]

Abstract: The genetic diversity and the essential oil variations within and among 12 Tunisian natural populations of Thymbra capitata (=Thymus capitatus Hoffm. et Link. = Coridothymus capitatus Rch. f.), from different geographic regions and bioclimates, were assessed using eight isozymes and thirty nine terpenoids. Volatiles were analyzed by gas chromatography (GC) and gas chromatography–mass spectrometry (GC–MS). A high genetic diversity within population which was revealed by isozymes (P =66.64%, Ap =1.85 and He =0.227) resulted from the great number of genotypes in the ancestral population before fragmentation, favored by the outbreeding of the species. Population structure depends on geographic distance between sites rather than bioclimate indicating isolation by distance. Cluster constructed using Nei''s genetic distances showed mainly geographic related population groupings. Essential oil composition varied among populations. UPGMA dendrogram based on Euclidean distance matrix among pairs of populations showed two major population aggregates. The chemical population structure is linked to the geographic distance among populations and ecological factors indicating that the local selective environmental factors act on chemical composition. The correlation between matrices of allozymes and terpenoids was not significant. Population differentiation performed on the two sets of data was similar to that probed by isozymes. The conservation strategies of populations should be made according to their level of genetic and chemical diversity in relation to geographic location of populations. [Copyright &y& Elsevier]

Abstract: Genetic and essential oil variations from eight Tunisian natural populations of Thymus algeriensis Boiss. et Reut. (Synonym Thymus hirtus Willd. subsp. algeriensis Boiss. et Reut.), a North African endemic species, were assessed using 47 terpenoids and 154 RAPD markers amplified by seven selected primers. Populations were collected from different geographical regions belonging to the sub-humid, upper semi-arid, mean semi-arid, lower semi-arid and upper arid bioclimates. Essential oil composition varied among populations. Five chemotypes according to main compounds have been distinguished: caryophyllene oxide/1,8-cineole/α-pinene, 1,8-cineole/α-pinene, 1,8-cineole/α-pinene/camphor, linalool and thymol chemotypes. A high genetic diversity within population and high genetic differentiation among them, based on RAPDs, were revealed (H pop =0.303 and G ST =0.339) caused both by the habitat fragmentation, the low size of most populations and the low level of gene flow among them. The genetic and chemical structures are in accordance with geography distances indicating isolation by distance. The UPGMA dendrogram and PCA analysis based on volatiles yielded higher separation among populations indicated specific adaptation of populations to the local environments. While the results obtained through RAPDs separated populations into three distinct clusters each of them including populations closed to their geographical origin. Genetic and chemical data were correlated based on Mantel test. Population differentiation performed on the two sets of data was similar to that shown using RAPDs suggesting higher accuracy of these markers. Given the high differentiation among all populations, conservation strategies should take into account genetic diversity and chemical variation levels in relation to bioclimatic and geographic location of populations. [Copyright &y& Elsevier]