Differential induction of chitinase activity in flax (Linum usitatissimum) in response to inoculation with virulent or avirulent strains of Melampsora lini, the cause of flax rust

Abstract

Chitinase enzymes are induced in many plants in response to pathogen challenge and other stress stimuli. Chitinase induction in flax leaves in response to inoculation with flax rust, caused by Melampsora lini (Pers.) Lev., was investigated in a line of flax (Forge) that has four resistance genes, viz. L6, M, N and P2. Four avirulent rust strains, each of which interacts with just one of the resistance genes in Forge, as well as a strain that is virulent on Forge, were used. Thus chitinase levels associated with resistance reactions triggered by the L6, M, N or P2 genes, and by a susceptible reaction, have been compared in the same host genotype. A marked increase in chitinase activity in inoculated leaves was observed with all four resistance reactions, with the increase occurring earlier with the P2 resistance reaction compared with the L6, M, and N reactions. A moderate increase in chitinase activity was also observed in systemic (new-growth) leaves of flax plants inoculated with strains interacting with the M, N or P2 genes. Leaves inoculated with a virulent strain of rust also had increased chitinase activity but the increase was much less than that found in leaves inoculated with the avirulent strains.