Stem rust of wheat caused by Puccinia graminis Pers. f.sp. trtici Eriks and E. Henn., is the most damaging fungal disease of both common (Triticum aestivum L.) and durum (Triticum turgidum L., ssp. Durum) wheat. Continuously emerging races virulent to many of the commercially deployed qualitative resistance genes have caused remarkable loss worldwide and threaten global wheat production. The objectives of this study were to evaluate the response of a panel of 283 durum wheat lines assembled by the International Maize and Wheat Improvement Center (CIMMYT) to multiple races of stem rust in East Africa at the adult plant stage and map loci associated with field resistance. The lines were evaluated in Debre Zeit, Ethiopia and Njoro, Kenya from 2018 to 2019 in five environments (year × season). The panel was genotyped using genotyping-by-sequencing. After filtering, 26,439 Single Nucleotide Polymorphism (SNP) markers and 280 lines and three checks were retained for analysis. Population structure was assessed using principal component analysis. Genome-wide association analysis (GWAS) was conducted using Genomic Association and Prediction Integrated Tool (GAPIT). The broad-sense heritability of the phenotype data revealed that 64–83% of the variation in stem rust response explained by the genotypes and lines with multiple race resistance were identified. GWAS analysis detected a total of 160 significant marker trait associations representing 42 quantitative trait loci. Of those, 21 were potentially novel and 21 were mapped to the same regions as previously reported loci. Known stem rust resistance genes/alleles were postulated including Sr8a, Sr8155B1, SrWeb/Sr9h, Sr11, Sr12, Sr13/Sr13 alleles, Sr17, Sr28/Sr16, Sr22, and Sr49. Lines resistant to multiple races in East Africa can be utilized as parents in durum wheat breeding programs. Further studies are needed to determine if there are new alleles at the Sr13 locus and potential markers for the known Sr13 alleles.

Many of the major stem rust resistance genes deployed in commercial wheat (Triticum spp.) cultivars and breeding lines become ineffective over time because of the continuous emergence of virulent races. A genome-wide association study (GWAS) was conducted using 26,439 single nucleotide polymorphism (SNP) markers and 280 durum wheat [Triticum turgidum L. subsp. Durum (Desf.) Husnot] lines from CIMMYT to identify genomic regions associated with seedling resistance to races TTKSK, TKTTF, JRCQC, and TTRTF and field resistance to TKTTF and JRCQC. The phenotypic data analysis across environments revealed 61-91 and 59-77% of phenotypic variation was explained by the genotypic component for seedling and adult plant response of lines, respectively. For seedling resistance, mixed linear model (MLM) identified eight novel and nine previously reported quantitative trait loci (QTL) while a fixed and random model circulating probability unification (Farm-CPU) detected 12 novel and eight previously reported QTL. For field resistance,

Stem rust caused by Puccinia graminis f.sp. tritici is one of the major biotic constraints of wheat production. The disease may cause substantial quantitative and qualitative yield losses but much of the work in Ethiopia on this pathosystem focuses on quantitative yield loss of durum wheat. This work was carried out at Debre Zeit Agriculture Research Centre during 2015/16 and 2016/17 main and off seasons. Hence the current study was conducted with the objectives to quantify the amount of loss in grain yield due to stem rust and assess the relationship between disease parameters, grain yield and physical quality parameters of improved durum wheat varieties grown in Ethiopia. Artificial inoculation was performed using a mixture of different dominant stem rust races. There were treated and untreated plots by fungicide that serves as protected and unprotected plots, respectively. Disease severity was recorded each 10 days interval and area under disease progress curve (AUDPC), terminal severity and coefficient of infection were calculated. The tested cultivars exhibited different disease severity level, having the mean value of 6.7-76%. High values of area under disease progress curve (AUDPC) were detected on Hitossa, Utuba (1225.7, 585.9). Whereas the lowest values of yield loss were recorded on cvs. Mangudo and Utuba having the mean value of yield loss 40.2 and 44.8%, respectively. The highest yield loss was observed on susceptible variety Hitosa showing the mean value of 70%. Correlation coefficients were tested between yield losses and values of AUDPC, final stem rust severity, coefficient of infection and rate of infection of the tested cultivars. There was strong correlation coefficients among disease parameters (r=0.72-0.99). There was also moderate strong negative correlation coefficient among disease parameters and yield, hectoliter weight and 1000-kernel weight of the test cultivars (r=-0.53 to -0.81). The current study indicated that application of Rex Duo can be used in minimizing yield losses caused by stem rust disease of durum wheat. Therefore, supporting the released durum wheat cultivars with fungicide application is the most pertinent issue in Ethiopia as most of the durum wheat cultivars in farmers hand were moderately susceptible to susceptible cultivars Pgt races.

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