Unlocking the story of resistance to Zymoseptoria tritici in Tunisian old durum wheat germplasm based on population structure analysis.

BACKGROUND: Septoria tritici blotch (STB) remains a significant obstacle to durum wheat cultivation on a global scale. This disease remains a challenge for farmers, researchers, and breeders, who are collectively dedicated to reduce its damage and improve wheat resistance. Tunisian durum wheat landraces have been recognized as valuable genetic ressources that exhibit resistance to biotic and abiotic stresses and therefore play a crucial role in breeding program aimed at creating new wheat varieties resistant to fungal diseases as STB, as well as adapted to climate change constraints. RESULTS: A total of 366 local durum wheat accessions were assessed for resistance to two virulent Tunisian isolates of Zymoseptoria tritici Tun06 and TM220 under field conditions. Population structure analysis of the durum wheat accessions, performed with 286 polymorphic SNPs (PIC > 0.3) covering the entire genome, identified three genetic subpopulations (GS1, GS2 and GS3) with 22% of admixed genotypes. Interestingly, all of the resistant genotypes were among GS2 or admixed with GS2. CONCLUSIONS: This study revealed the population structure and the genetic distribution of the resistance to Z. tritici in the Tunisian durum wheat landraces. Accessions grouping pattern reflected the geographical origins of the landraces. We suggested that GS2 accessions were mostly derived from eastern Mediterranean populations, unlike GS1 and GS3 that originated from the west. Resistant GS2 accessions belonged to landraces Taganrog, Sbei glabre, Richi, Mekki, Badri, Jneh Khotifa and Azizi. Furthermore, we suggested that admixture contributed to transmit STB resistance from GS2 resistant landraces to initially susceptible landraces such as Mahmoudi (GS1), but also resulted in the loss of resistance in the case of GS2 susceptible Azizi and Jneh Khotifa accessions.

Morphological characterization and genetic diversity analysis of Tunisian durum wheat (Triticum turgidum var. durum) accessions.

BACKGROUND: Tunisia is considered a secondary center of diversification of durum wheat and has a large number of abandoned old local landraces. An accurate investigation and characterization of the morphological and genetic features of these landraces would allow their rehabilitation and utilization in wheat breeding programs. Here, we investigated a diverse collection of 304 local accessions of durum wheat collected from five regions and three climate stages of central and southern Tunisia. RESULTS: Durum wheat accessions were morphologically characterized using 12 spike- and grain-related traits. A mean Shannon-Weaver index (H') of 0.80 was obtained, indicating high level of polymorphism among accessions. Based on these traits, 11 local landraces including Mahmoudi, Azizi, Jneh Khotifa, Mekki, Biskri, Taganrog, Biada, Badri, Richi, Roussia and Souri were identified. Spike length (H' = 0.98), spike shape (H' = 0.86), grain size (H' = 0.94), grain shape (H' = 0.87) and grain color (H' = 0.86) were the most polymorphic morphological traits. The genetic diversity of these accessions was assessed using 10 simple sequence repeat (SSR) markers, with a polymorphic information content (PIC) of 0.69. Levels of genetic diversity were generally high (I = 0.62; He = 0.35). In addition, population structure analysis revealed 11 genetic groups, which were significantly correlated with the morphological characterization. Analysis of molecular variance (AMOVA) showed high genetic variation within regions (81%) and within genetic groups (41%), reflecting a considerable amount of admixture between landraces. The moderate (19%) and high (59%) levels of genetic variation detected among regions and among genetic groups, respectively, highlighted the selection practices of farmers. Furthermore, Mahmoudi accessions showed significant variation in spike density between central Tunisia (compact spikes) and southern Tunisia (loose spikes with open glume), may indicate an adaptation to high temperature in the south. CONCLUSION: Overall, this study demonstrates the genetic richness of local durum wheat germplasm for better in situ and ex situ conservation and for the subsequent use of these accessions in wheat breeding programs.

Technological and safety properties of Lactobacillus plantarum strains isolated from a Tunisian traditional salted meat.

A total of 17 strains of Lactobacillus plantarum, isolated from a Tunisian traditional salted meat and identified by biochemical and molecular methods, were characterized according to their technological properties including acidifying, antimicrobial and enzymatic activities as well as antibiotic resistance in order to select the most suitable for use as starter cultures for the production of fermented sausages. All the strains studied showed good acidifying activity and were able to reduce the pH to less than 4.3 in 72, 48 and 24h at 15, 25 and 37°C respectively. The majority of strains displayed antimicrobial activities against Salmonella arizonae, Staphylococcus aureus, Pseudomonas aeuroginosa and Escherichia coli, however characterization of the antimicrobial substances showed that none of the strains could produce bacteriocins. All the L. plantarum strains were able to hydrolyze casein, whereas none of them was found to possess lipolytic activity. The majority of strains of L. plantarum were resistant to tetracycline, erythromycin, rifampicin, ampicillin and penicillin G.

Genetic diversity and population structure of six species of Capparis in Tunisia using AFLP markers.

In order to study the genetic diversity, the phylogeographic pattern and hybridization between six Tunisian Capparis species, 213 accessions of Caper were genotyped with three primer combinations of amplified fragment length polymorphism (AFLP) markers. Out of 750 fragments generated, 636 were polymorphic and 407 of them were restricted to a single species. STRUCTURE and PCoA analyses clearly separated morphologically different populations into six distinct genetic ones. The UPGMA analysis grouped the species into three main clusters: G1 grouped C. spinosa subsp. spinosa var. spinosa and C. sicula subsp. sicula; G2 grouped C. ovata subsp. ovata and C. orientalis and G3 clustered C. zoharyi and C. aegyptia. Populations from G1, G2 and G3 were mainly distributed in arid, subhumid, and semi-arid bioclimates, respectively. Additional genetic studies on Capparis could help to identify genes underlying speciation events and local adaptation to geographic areas leading to the development of breeding programs.