Assessment of Lr20 gene-specificity of symptom elicitation by intercellular fluids from leaf rust-infected wheat leaves

Paleness, chlorosis and necrosis were caused in uninfected primary leaves of three Lr2O-bearing wheat cultivars after infiltration with fluids from intercellular spaces of leaves of Triticum aestivum cv. Chinese Spring infected by mycelia of leaf rust (Puccinia recondita Esp. tritici) either avirulent or virulent with respect to the Lr20 allele. No symptoms were caused in cv. Chinese Spring or two other cultivars, all of which lack Lr genes, or in cv. Brevit which bears the Lr2c allele. Symptoms were caused, however, in the Lr14a-bearing cv. Spica. Symptoms were not caused in a Chinese Spring/Axminster line in which chromosome 7A carrying the Lr20 allele had been substituted from the cv. Axminster. No symptoms were caused in any cultivar by fluids from uninfected leaves.

The eliciting agents were partially thermostable macromolecules which were active after many-fold dilution and likely to have been derived from either walls of intercellular hyphae or host cells at the infection court.