Inoculum pressure and the development of stem rust epidemics in barley

The effects of inoculum pressure on the development of epidemics of Puccinia graminis tritici in two barley cultivars with different levels of resistance were examined in two field experiments. Treatments were established by inoculation of foci within plots and/or the strategic use of fungicides. Additional ‘rust-free’ treatments were maintained to provide comparisons of grain yield and quality. Relationships between rust severity, rust incidence and grain yield and quality were also examined. Initial inoculum levels were important in determining disease severity and incidence for individual epidemics; however, severe epidemics developed under most ‘rusted’ treatments of the susceptible cultivar Galleon and reduced grain yield by up to 58%. Epidemics under corresponding treatments of the moderately resistant cultivar Grimmett were less severe, and the value of the resistance was evident with yield losses not exceeding 12%. Yield reductions were usually associated with reduced grain size and weight.