Field Resistance to Scald Disease of Barley,Rhynchosporium secalis (Ayres) Davis: Slow-Scalding

Slow-scalding resistance (S-SR), is a new phenomenon in barley breeding programs, which due to the instability of major gene type of resistance has been gaining increasing attention. In order to determine presence of genotypes with S-SR, quantitative resistance of 50 barley genotypes with different reactions to the scald disease were studied using an alpha lattice design with three replications at two research stations in Canada (in Edmonton for three and in Lacombe for two years) and one location in Mexico (in Toluca for two years). For a better understanding of the genotypes’ reactions against the disease, nine differentials with known major genes for resistance to R. secalis were included in the experiments. Applying artificial inoculation of a mixture of six different single-spore isolates of the scald fungus, to measure disease progress, multiple disease assessments were undertaken for the disease severity and incidence under field conditions. Based on combined analyses of data, the genotypes were compared and the effects of genotypes, environments and genotype × environment interaction found to be significant. The results revealed that both disease severity and incidence showed a low rate of progress in slow-scalding lines. The reactions of all genotypes tested were further classified into resistant, slow-scalder, intermediate, and susceptible/fast-scalder categories using hierarchical cluster analysis. Interestingly, It was revealed that the Rh4 gene could play an important role in stability/durability of resistance in all studied environments. Slow-scalding genotypes such as UNA80, Osiris and Zavila revealed to be useful as desirable resources in barely breeding programs.