CHANGES IN THE LEVELS OF PEROXIDASE AND PHENYLALANINE AMMONIA-LYASE IN BRASSICA-NAPUS CULTIVARS SHOWING VARIABLE RESISTANCE TO LEPTOSPHAERIA-MACULANS

Peroxidase and phenylalanine ammonia-lyase activities (PAL) were determined in leaves of healthy and inoculated Brassica napus cultivars, showing differential disease reaction towards a virulent and a weakly virulent strain of Leptosphaeria maculans, the black leg pathogen. Both enzymes showed increased activities as the result of inoculation, PAL activity increasing as early as 12 h after inoculation. The most significant increase in both peroxidase and PAL activity was observed when the moderately resistant cultivar, Cresor, was challenged with the weakly virulent strain. Highest activity of the two enzymes was detected 2 d after inoculation. Very low peroxidase activity was detected in both strains of L maculans, while no PAL activity was detectable in either of the strains. Cytochemical tests revealed increased peroxidase activity following inoculation, mainly in the epidermal and guard cells.