Abstract

Yellow rust, caused by Puccinia striiformis f. sp. tritici, is one of the most important diseases of wheat in Ethiopia. Poor knowledge of resistance genes deployed in Ethiopian wheat cultivars is one major factor for recurrent epidemics of rust diseases. Molecular marker based gene identification showed the presence of Yr1, Yr4, Yr6, Yr7, Yr9, Yr10, Yr17 and Yr18 in various frequencies, whereas Yr8 was not detected in any of the tested 74 bread wheat genotypes. Yr7 was the most frequent (74%) followed by Yr6 (56%) and Yr 18 (37%) whereas Yr1 and Yr4 were detected in lower frequency (7 and 14%), respectively. The contribution of each Yr gene was evaluated in yellow rust differential lines possessing various genes. The differential lines carrying Yr9 and Yr8 had the highest average coefficient of infection (ACI) value (83 each) followed by Yr6 and Yr7 with ACI values of 82 and 80, respectively. The lowest ACI value (46.4) was exhibited on a differential line that carried Yr4. The number of Yr genes identified from the tested genotypes varied from 0 to 5. The ACI value exhibited by varieties possessing the maximum number of five resistance genes was 42. The majority (26 genotypes representing 35%) of the genotypes possessed three genes with an average coefficient of infection of 42. Pyramiding of the identified genes does not provide sufficient protection against yellow rust in Ethiopia. Thus, there is urgent need for searching for more effective resistance genes to be incorporated in Ethiopian bread wheat cultivars.

Key words: Average coefficient of infection (ACI), bread wheat, molecular markers, wheat genotypes, Yr genes.