RESISTANCE AND TOLERANCE TO LEAF RUST IN ETHIOPIAN TETRAPLOID WHEAT LANDRACES

Infection type to leaf rust (Puccinia recondita f. sp. tritici) in Eth iopian tetraploid wheat (Triticum turgidum L.) landraces is almost inv ariably susceptible and disease severity is usually high. However, suc h wheats produce a stable yield and seeds are less shrivelled, relativ e to disease severity. Using 10 'pure-line' genotypes, the effect of t he disease on kernel weight and grain yield was studied to detect whet her some form of incomplete resistance or tolerance was involved. Geno types exhibited significant differences for mean disease severity. Per centage 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. O nly one genotype sustained significant losses of both kernel weight an d 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. Generall y, 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 n ot be explained by differences in disease severity, and percentage los s did not appear to be a function of disease severity.