Morphological Characterization and Genetic Diversity Analysis of a Tunisian Durum Wheat (Triticum Turgidum Var. Durum) Collection

Background: Tunisia is a center of genetic diversity 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 use for practical and beneficial purposes. In this context, a collection of 304 local accessions of durum wheat, collected from five regions and three climatic zones of central and southern Tunisia, was studied. Results: Morphological characterization was carried out using 12 spike-related traits and rendered a mean Shannon-Weaver Index (H') of 0.80 indicating the presence of a high level of polymorphism among accessions. Based on these traits 11 local landraces, namely Mahmoudi, Azizi, Jneh Khotifa, Mekki, Biskri, Taganrog, Biada, Badri, Richi, Roussia and Souri were identified. Spike length (H’=0.98) and shape (H’=0.86) with grains size (H’=0.94), form (H’=0.87) and color (H’=0.86) were the most polymorphic morphological traits. The genetic diversity was assessed using 10 SSR markers, with a polymorphic information content (PIC) of 0.69. Levels of genetic diversity were generally high, with a Shannon's Information Index (I) of 0.62 and a gene diversity (He) of 0.35. In addition, population structure analysis distinguished 11 genetic groups resulted from STRUCTURE and Mantel test showed a significant correlation between genetic and morphological distances. Analysis of molecular variance (AMOVA) showed high genetic variations within regions (81%) and wheat subpopulations (41%) showing a considerable amount of admixture between landraces realized by farmers; as well as a moderate (19%) and high (59%) genetic variations among regions and wheat subpopulations, indicating practices of selection pressure conducted by farmers. The Mahmoudi landrace showed spike densities significantly different between the center to the south of Tunisia; notably loose spikes with open glumes in the south and compact ones in the center, which may represent an adaptation form for tolerance to high temperature. Conclusion: Overall, this study highlights the genetic richness of local resources for better in situ or ex situ conservation and for their subsequent use in plant breeding programs.