Resistance and tolerance to leaf rust in Ethiopian tetraploid wheat landraces

Infection type to leaf rust (Puccinia recondita f. sp. tritici) in Ethiopian tetraploid wheat (Triticum turgidum L.) landraces is almost invariably susceptible and disease severity is usually high. However, such wheats produce a stable yield and seeds are less shrivelled, relative to disease severity. Using 10 'pure-line' genotypes, the effect of the disease on kernel weight and grain yield was studied to detect whether some form of incomplete resistance or tolerance was involved. Genotypes exhibited significant differences for mean disease severity. Percentage losses varied from 3.9 to 14.4% for kernel weight and from 2.8 to 31.3% for grain yield. Regression analysis revealed a significant linear relationship (r = 0.66, P < 0.05) between mean percentage loss and mean disease severity for kernel weight but not for grain yield. Only one genotype sustained significant losses of both kernel weight and grain yield, and was therefore classified as susceptible. Genotypic differences for both traits and the negative correlation (r = -0.87, P < 0.01) between them complicated interpretation of the data. Generally, however, the results indicated that incomplete resistance, possibly partial resistance, is present when one considers kernel weight. For grain yield, tolerance was also implicated since the variation could not be explained by differences in disease severity, and percentage loss did not appear to be a function of disease severity.