SNP-based Genetic Structure of Tunisian Durum Wheat Landraces and Distribution of the Resistance to Septoria Tritici Blotch

Background: Septoria tritici blotch (STB) has marked durum wheat production worldwide. This fungal disease is until today a challenge for farmers, researchers and breeders all united in the aim of reducing its damage and improving wheat resistance. Tunisian durum wheat landraces were reported to be valuable genetic resources for resistance to biotic and abiotic stresses and are therefore prominently deployed in breeding programs to develop new varieties adapted to fungal diseases as STB and to climate change constraints overall.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. The grouping pattern of accessions appear to be associated, to some extent, with the geographical pattern of the landraces. We suggested that GS2 accessions were mostly introduced 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 suscpetible Azizi and Jneh Khotifa accessions.

SNP-Based Genetic Structure of Tunisian Durum Wheat Landraces and Distribution of the Resistance to Septoria Tritici Blotch

Background: Septoria tritici blotch (STB) has marked durum wheat production worldwide. This fungal disease is until today a challenge for farmers, researchers and breeders all united in the aim of reducing its damage and improving wheat resistance. Tunisian durum wheat landraces were reported to be valuable genetic resources for resistance to biotic and abiotic stresses and are therefore prominently deployed in breeding programs to develop new varieties adapted to fungal diseases as STB and to climate change constraints overall.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. The grouping pattern of accessions appear to be associated, to some extent, with the geographical pattern of the landraces. We suggested that GS2 accessions were mostly introduced 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 suscpetible Azizi and Jneh Khotifa accessions.

Genome-Wide Association Analysis for Stem Cross Section Properties, Height and Heading Date in a Collection of Spanish Durum Wheat Landraces

Durum wheat landraces have a high potential for breeding but they remain underexploited due to several factors, including the insufficient evaluation of these plant materials and the lack of efficient selection tools for transferring target traits into elite backgrounds. In this work, we characterized 150 accessions of the Spanish durum wheat collection for stem cross section, height and heading date. Continuous variation and high heritabilities were recorded for the stem area, pith area, pith diameter, culm wall thickness, height and heading date. The accessions were genotyped with DArTSeq markers, which were aligned to the durum wheat ‘Svevo’ genome. The markers corresponding to genes, with a minor allele frequency above 5% and less than 10% of missing data, were used for genome-wide association scan analysis. Twenty-nine marker-trait associations (MTAs) were identified and compared with the positions of previously known QTLs. MTAs for height and heading date co-localized with the QTLs for these traits. In addition, all the MTAs for stem traits in chromosome 2B were located in the corresponding synteny regions of the markers associated with lodging in bread wheat. Finally, several MTAs for stem traits co-located with the QTL for wheat stem sawfly (WSS) resistance. The results presented herein reveal the same genomic regions in chromosome 2B are involved in the genetic control of stem traits and lodging tolerance in both durum and bread wheat. In addition, these results suggest the importance of stem traits for WSS resistance and the potential of these landraces as donors for lodging tolerance and WSS resistance enhancement. In this context, the MTAs for stem-related traits identified in this work can serve as a reference for further development of markers for the introgression of target traits into elite material.

Unlocking the Patterns of the Tunisian Durum Wheat Landraces Genetic Structure Based on Phenotypic Characterization in Relation to Farmer’s Vernacular Name

During the 1970s, Tunisian durum wheat landraces were replaced progressively by modern cultivars. These landraces are nowadays maintained by smallholder farmers in some ecological niches and are threatened gradually by extinction resulting in the narrowing of the genetic diversity. This study aims to investigate patterns of phenotypic variability using twelve quantitative traits in a panel of 189 durum wheat landraces and seven checks, based on farmer’s population name attribution and genetic structure. Our results showed high phenotypic variability among and within landraces and checks for ten out of twelve studied traits. The principal components analysis showed similar grouping using farmers name attribution and genetic structure using K = 6. These results confirmed the identification of a new gene pool in the oases of Tunisia, represented by the sub-population Jenah Zarzoura and the robustness and high relationships between phenotypic and genome-wide genetic structure using DArTseq method. These findings will enhance the conservation efforts of these landraces and their use in breeding efforts at national and international levels to adapt to dry conditions.

Genetic Diversity of Omani Durum Wheat (Triticum turgidum sub sp. durum) Landraces

Introduction: The Sultanate of Oman is rich in diversity of the most important crops like wheat, which not only has a global significance but is also regarded as one of the strategic crops in the country. The country has an ancient cultivation history of both bread wheat (Triticum aestivum L.s.l.) and durum wheat (Triticum turgidum sub sp. durum) because of its characteristic location on the eastern edge of the Arabian Peninsula. Wheat landraces constitute the prime genetic resources of cultivated wheat not only in Oman but also in several MENA (the Middle East and North Africa) countries. Indigenous landraces have paramount significance for their potential utilization in crop improvement and conservation programs. Hence, the present study was undertaken to subject 17 indigenous durum wheat accessions for analyses of diversity to select parents for hybridization in national crop improvement programs. Materials and Methods: The trial was conducted consecutively for two cropping seasons (2017-2018 and 2018-2019) during winter from November to March on the layouts of a loamy soil site under sprinkler irrigation system in Augmented Design with five check varieties replicated five times randomized and distributed throughout the experimental area under spacing and crop husbandry practices as per national recommendations. The data on 9 quantitative (Plant descriptors) and 6 qualitative traits on the presence (score 1) or absence (score 0) of pigmentation on 6 plant parts were collected. These traits were subjected to both Principal Component Analysis (PCA) and Hierarchical Cluster Analysis (HCA) to comprehend the contribution of these characters towards diversity and form prime diverse clusters from 17 indigenous durum wheat landraces to select appropriate parents for crossing. Results: The results indicated that indigenous durum wheat accessions were significantly different (p>0.05) with respect to all the quantitative characters except the number of tillers. Of 36 combinations of associations among 9 agro-morphological characters’ studied, only six correlations involving four characters viz. tiller no., spikelets/ spike, grains/spike, and grain length were found significant (p<0.05). The results of two multivariate analyses indicated the formation of four diverse clusters with different compositions of accessions, thus not supporting each other in discerning diversity. The parents were selected for hybridization for improving characters of growth for higher yield or productivity with one or two identifying markers of pigmentation on plant parts. Conclusion: The indigenous durum wheat landraces / accessions were found to be more diverse and potential for use in the national crop improvement programs for higher productivity.

Genetic diversity of Ethiopian durum wheat landraces

Genetic diversity and population structure assessment in crops is essential for marker trait association, marker assisted breeding and crop germplasm conservation. We analyzed a set of 285 durum wheat accessions comprising 215 Ethiopian durum wheat landraces, 10 released durum wheat varieties, 10 advanced durum wheat lines from Ethiopia, and 50 durum wheat lines from CIMMYT. We investigated the genetic diversity and population structure for the complete panel as well as for the 215 landraces, separately based on 11,919 SNP markers with known physical positions. The whole panel was clustered into two populations representing on the one hand mainly the landraces, and on the other hand mainly released, advanced and CIMMYT lines. Further population structure analysis of the landraces uncovered 4 subgroups emphasizing the high degree of genetic diversity within Ethiopian durum landraces. Population structure based AMOVA for both sets unveiled significant (P < 0.001) variation between populations and within populations. Total variation within population accessions (81%, 76%) was higher than total variation between populations (19%, 24%) for both sets. Population structure analysis based genetic differentiation (FST) and gene flow (Nm) for the whole set and the Ethiopian landraces were 0.19 and 0.24, 1.04, and 0.81, respectively indicating high genetic differentiation and limited gene flow. Diversity indices verify that the landrace panel was more diverse with (I = 0.7, He = 0.46, uHe = 0.46) than the advanced lines (I = 0.6, He = 0.42, uHe = 0.42). Similarly, differences within the landrace clusters were observed. In summary a high genetic diversity within Ethiopian durum wheat landraces was detected, which may be a target for national and international wheat improvement programs to exploit valuable traits for biotic and abiotic stresses.

The Adoption of Landraces of Durum Wheat in Sicilian Organic Cereal Farming Analysed Using a System Dynamics Approach

The adoption of rare, traditional crops represents a good example of enhancing functional agrobiodiversity, not only to provide benefits for farmers but also for society as a whole. The study outlined in this paper aims to verify how and under local social-ecological conditions the combination of organic cereal farming and growing of durum wheat landraces can be profitably applied. Focusing on Sicily as one of the most developed cereal systems existing in southern Italy, the study deployed a comparison between data from the regional dataset by the Farm Accountancy Data Network (FADN) and the data provided by the Association of farmers called Simenza. Thereafter, we used a System Dynamics Approach (SDA) for a better understanding of the main drivers which will most likely affect the profitability of the system in the medium and long term. The results clearly demonstrated how the durum wheat organic system under investigation might still develop under the push of an increasing relative economic advantage between standard varieties and landraces.

Unlocking the Patterns of the Tunisian Durum Wheat Landraces Genetic Structure Based on Phenotypic Characterization in Relation to Farmer’s Vernacular Name

During the 1970s, Tunisian durum wheat landraces were replaced progressively by modern cultivars. These landraces are nowadays maintained by smallholder farmers in some ecological niches and are threatened gradually by extinction resulting on the narrowing of the genetic diversity. This study aims to investigate patterns of phenotypic variability using twelve quantitative traits in a panel of 189 durum wheat landraces and seven checks, based on farmer&rsquo;s population name attribution and genetic structure. Our results showed high phenotypic variability among and within landraces and checks for the majority of the studied traits. The principal components analysis showed similar grouping using farmers name attribution and genetic structure using K = 6, which confirmed the identification of a new gene pool in the oases of Tunisia, represented by the sub-population Jenah Zarzoura and the robustness and high relationships between phenotypic and genome-wide genetic structure using DArTseq method. These findings will enhance the conservation efforts of these landraces and their use in breeding efforts at national and international levels to adapt to dry conditions.

Life story of Tunisian durum wheat landraces revealed by their genetic and phenotypic diversity

Durum wheat (Triticum turgidum L. subsp. durum) landraces represent a prominent genetic resource for Mediterranean farming systems and breeding programs. Fourteen landraces sampled in Tunisia were genotyped with 9 microsatellite markers and characterized with 15 morphological descriptors, including resistance to the fungal disease Septoria tritici blotch (STB). The genetic diversity, nearly was as important within landraces populations (45%) than between populations (54%). It was structured in seven genetic groups and was only partly explained by the variety name or the locality of origin. Populations were also greatly diversified phenotypically (Shannon-Weaver H’=0.54) with traits related to spike and awn colours being the most diversified. Resistance to STB was either qualitative in two populations or with varying degrees of quantitative resistance in the others. A Pst-Fst comparison indicate a local adaptation of the populations. Overall, the genetic structure of Tunisian durum wheat landraces revealed a complex selection trajectory and seed exchanges between farmers.