Septoria tritici blotch (STB) is a devastating fungal disease affecting durum and bread wheat cultivation worldwide. The identification, development, and employment of resistant wheat genetic material is the key to overcoming costs and limitations of fungicide treatments. The search for resistance sources in untapped genetic material may speed up the deployment of STB genetic resistance in the field. Ethiopian durum wheat landraces represent a valuable source of such diversity. In this study, 318 Ethiopian durum wheat genotypes, for the most part traditional landraces, were phenotyped for resistance to different aspects of STB infection. Phenology, yield and yield component traits were concurrently measured the collection. Here we describe the distribution of STB resistance traits in modern varieties and in landraces, and the relation existing between STB resistance and other agronomic traits. STB resistance sources were found in landraces as well as in modern varieties tested, suggesting the presence of alleles of breeding relevance. The genetic material was genotyped with more than 16 thousand genome-wide polymorphic markers to describe the linkage disequilibrium and genetic structure existing within the panel of genotypes, and a genome-wide association (GWA) study was run to allow the identification of genomic loci involved in STB resistance. High diversity and low genetic structure in the panel allowed high efficiency GWA. The GWA scan detected five major putative QTL for STB resistance, only partially overlapping those already reported in the wheat literature. We report four putative loci for Septoria resistance with no match in previous literature: two highly significant ones on Chr 3A and 5A, and two suggestive ones on Chr 4B and 5B. Markers underlying these QTL explained as much as 10% of the phenotypic variance for disease resistance. We found three cases in which putative QTL for agronomic traits overlapped marker trait association deriving from STB GWA. Our results show that the Ethiopian untapped allelic diversity bears a great value in studying the molecular basis of STB resistance and in breeding for resistance in local and international material.

Summary The Ethiopian plateau hosts thousands of durum wheat ( Triticum turgidum subsp. durum ) farmer varieties ( FV ) with high adaptability and breeding potential. To harness their unique allelic diversity, we produced a large nested association mapping ( NAM ) population intercrossing fifty Ethiopian FV s with an international elite durum wheat variety (Asassa). The Ethiopian NAM population (Et NAM ) is composed of fifty interconnected bi‐parental families, totalling 6280 recombinant inbred lines ( RIL s) that represent both a powerful quantitative trait loci ( QTL ) mapping tool, and a large pre‐breeding panel. Here, we discuss the molecular and phenotypic diversity of the Et NAM founder lines, then we use an array featuring 13 000 single nucleotide polymorphisms ( SNP s) to characterize a subset of 1200 Et NAM RIL s from 12 families. Finally, we test the usefulness of the population by mapping phenology traits and plant height using a genome wide association ( GWA ) approach. Et NAM RIL s showed high allelic variation and a genetic makeup combining genetic diversity from Ethiopian FV s with the international durum wheat allele pool. Et NAM SNP data were projected on the fully sequenced AB genome of wild emmer wheat, and were used to estimate pairwise linkage disequilibrium ( LD ) measures that reported an LD decay distance of 7.4 Mb on average, and balanced founder contributions across Et NAM families. GWA analyses identified 11 genomic loci individually affecting up to 3 days in flowering time and more than 1.6 cm in height. We argue that the Et NAM is a powerful tool to support the production of new durum wheat varieties targeting local and global agriculture.

Background Septoria tritici blotch (STB) (Zymoseptoria tritici) is a major disease of durum wheat, an economic crop grown in the highlands of Wollo in Ethiopia. Methods To determine the status of this disease, we conducted surveys in five districts of Wollo (Meket, Woreilu, Wadila, Jama, and Dessie Zuria) during the 2015 cropping season. We visited 75 farm plots to determine the prevalence, incidence, and severity of STB. Results STB prevalence varied among locations, genotypes, planting dates, growth stages, previous crops, plant population, weed population, and soil types. Similarly, disease intensity also varied along all independent variables. The level of incidence was high in all the visited districts, and the level severity ranged from 9.9 to 59.3% while the incidence varied from 50 to 100%. The mean differences in incidence and severity within the districts’ variable classes, altitude, varieties, growth stage, plant population, planting date, previous crop, weed population, and soil type were high. The independent variables, districts, altitude, varieties, growth stage, plant population, planting date, previous crops, weed population, and soil type, were significantly associated with high incidence and severity of STB as single predictor in the logistic regression model. A reduced multiple variable model was fitted using districts, altitude, varieties, growth stage, plant population, planting date, previous crop, weed population, and soil type as independent variables. High incidence (> 50%) and severity (> 25%) had a high probability of association to all independent variables, except previous crop. Low disease incidence (≤ 50%) and low disease severity (≤ 25%) had high probability of association to the previous crop. Conclusion Environmental variables, cultivation practice, and responses were important for the development of STB. Therefore, these factors must be considered in designing strategies for the effective management of STB.