Effects of Nitrogen Fertilization on Disease Severity and Infection Type of Yellow Rust on Wheat Genotypes Varying in Quantitative Resistance

Two experiments were carried out to study the effect of nitrogen level on disease severity of genotypes of wheat ( Triticum aestivum ) varying in quantitative resistance to yellow rust, caused by Puccinia striiformis. In 1990, nine wheat genotypes were exposed to 0.20, 40 and 80 kg N per ha. In 1991, six genotypes, selected from experiment I, were examined at 0. 30 and 90 kg N per ha. The N was applied in the form of calcium ammonium nitrate (NH 4 NO 3 +CaCO 3 ). In both years the disease severity increased strongly with increased N‐levels. The infection types also increased with increased N‐levels. Compared with the main effects, the Genotype X N‐level, the Genotype X Year and the Genotype X N‐level, X Year interactions were small, but highly significant (at P = 0.01). Selection for quantitative resistance therefore has to be carried out at the N‐levels used in the regions the breeding is aiming at.