Development of Ethiopian barley genotypes with combined resistance to leaf scald (Rhynchosporium secalis) and net blotch (Pyrenophora teres)

Barley is one of the oldest and genetically most diverse cereal crops in Ethiopia. Since several years, however, the national average yield of the crop remains to be only 1 t/ha. Because major production of barley still largely depends on the traditional varieties and farming practices, this is assumed to be one of the constraints accounting for its low yield. In addition, cultivation of barley in marginal areas with low soil fertility, drought in the lowlands, frost in the highland, diseases and pests are assumed to contribute to the low yield of the crop. Among the nearly 40 diseases reported on barley, mainly leaf scaled (R. secalis) and net blotch (p. teres) limit its productivity. The development of new genotypes with combined resistance to these two important diseases in Ethiopia was the major topic of the present study. Before initiating the resistance breeding itself, it was essential to understand the pathogenic variability of the two pathogens, the kind and level of resistance in the crop and the interaction between the two. Barley leaf samples with scald symptoms collected from different genotypes and locations in Ethiopia were used to isolate R. secalis. Then the virulence of 24 isolates was studied on seedlings and adult plants of 14 barley differential genotypes. With a fairly small number of isolates a wide variability of the fungus was proven in which the 24 isolates were classified into 17 distinct pathotypes. The pathotypes were designated in increasing order based on the number of genes matched. Hence, pathotypes 16 and 17 were the most complex ones, each overcoming the resistance of 11 of the 14 tested differentials. Resistance to leaf scald detected at the seedling stage is expected to be effective at all growth stages since a highly significant relationship was observed between the seedling and the adult plant tests with the differentials. Hence, the seedling test is a valid test to evaluate genotypes for resistance and to differential genotypes. As a result, five of the eight isolates were found to be virulent on CI 5791, an Ethiopian genotype still known world wide as a good source of resistance to the disease.