Abstract:
Wheat stem rust (Puccinia graminis f.sp. tritici) is one of the most destructive and devastating foliar diseases of wheat, which causes considerable yield losses worldwide. Researchers often seek to incorporate new sources of resistance in the breeding program due to the emergence and rapid spread of virulent races of wheat stem rust. The objectives of this study were to:(1) investigate the distribution and importance of wheat stem rust in the North Shewa Zones of Amhara and Oromia regions; and (2) evaluate durum wheat landrace accessions against four races (TTKSK, TKTTF, TRTTF, and JRCQC) at seedling and in the field under natural infections. Stem rust survey was carried out diagonally along each field using a 1 m2 quadrant on 64 farmers’ fields in 11 districts. A total of 34 durum wheat accessions from gene bank of Ethiopian Biodiversity Institute (EBI) and susceptible checks were used for seedling and field tests. Out of 56 the total stem rust samples collected, 31 viable isolates were used for race analyse. Four dominant stem rust races from Ambo were used to evaluate the durum wheat accessions. Race identification and seedling tests were conducted according to the standard methods in the greenhouse at Ambo Agricultural Research Center. Field evaluations were done at Debre-Zeit Agricultural Research Center using simple lattice 6 x 6 designs with two replications and two checks per block during 2019 main season. According to the survey results 87.5% of the fields were infected by wheat stem rust. The highest mean disease incidence (95%) and severity (68.33%) were noted at Minjar Shenkora whereas; the lowest incidence (20%) and severity (13.69%) at Basona Werana and Moretna Jiru, respectively. All bio-physical factors were significantly (P≤0.05) associated with wheat stem rust epidemics. A total of six races (TKTTF, TTTTF, TTRTF, TKKTF, TTKTT, and TTKTF) were identified. The most predominant race was TKKTF (61%) followed by TTTTF (13%) and TKTTF (10%). Race TTKTT was the most virulent on 19 stem rust resistance genes (all except Sr36). Seedling evaluation results showed variability in responses of genotypes for the four stem rust races. Two accessions (TD3750 and TD3751) were found resistanct to the prevailing races both at seedling and field conditions and two accessions (TD5917 and TD8778) were resistant to field conditions. This study indicated the wide distribution of stem rust and and prevalence of virulent races in East Shewa zones of Amhara and Oromia. The newly identified resistance sources would be exploited in the breeding program. Wheat stem rust monitoring and searching for new sources of resistance should be exploited in durum wheat landraces from gene banks
