Effect of leaf rust ( Puccinia recondita tritici) on yield of four isogenic wheat lines

Abstract

Four near-isogenic lines of wheat (Thatcher and Thatcher backcross lines with Lr3b, Lr16 and Lr9) with different levels of resistance to leaf rust were used to determine the relationship between disease severity and yield loss in the greenhouse and the field. Larger areas under the disease progress curves were associated with greater host susceptibility. Yield losses varied from 21% to 47% depending on the susceptibility of the lines and the severity of the epidemics. Yield loss measured varied with the size of the plot harvested. Percentage yield losses from each line in the field experiment were pooled and regressed against the area under the disease progress curve of disease severity on flag leaf and the mean severity per tiller. Both regressions were highly significant with R 2 of 0·89 and 0·88, respectively. The ratio of area under the disease progress curve to yield loss was higher in susceptible than resistant cultivars; thus it was difficult to ascertain whether a linear or S-shaped curve was more appropriate for the disease-loss relationship.