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

Chitinase enzymes are induced in many plants in response to pathogen challe nge and other stress stimuli. Chitinase induction in flax leaves in respons e to inoculation with flax rust, caused by Melampsora lini (Pers.) Lev., wa s investigated in a line of flax (Forge) that has four resistance genes, vi z. L6, M, N and P2. Four avirulent rust strains, each of which interacts wi th just one of the resistance genes in Forge, as well as a strain that is v irulent on Forge, were used. Thus chitinase levels associated with resistan ce reactions triggered by the L6, M, N or P2 genes, and by a susceptible re action, have been compared in the same host genotype. A marked increase in chitinase activity in inoculated leaves was observed with all four resistan ce reactions, with the increase occurring earlier with the P2 resistance re action compared with the L6, M, and N reactions. A moderate increase in chi tinase activity was also observed in systemic (new-growth) leaves of flax p lants inoculated with strains interacting with the M, N or P2 genes. Leaves inoculated with a virulent strain of rust also had increased chitinase act ivity but the increase was much less than that found in leaves inoculated w ith the avirulent strains.