Variability of phenylalanine ammonia-lyase and peroxidase activities in leaves of subterranean clover is determined by their susceptibility to Kabatiella caulivora

Abstract

Kabatiella caulivora is the causal organism of northern anthracnose or clover (Trifolium spp.) scorch disease. The activities of phenylalanine ammonia-lyase (PAL) and soluble peroxidase were determined in seedling leaves of two cultivars of subterranean clover (T. subterraneum) inoculated with race 1 or race 2 of K. caulivora. A small increase in activity of PAL was recorded in both cultivars 2–4 h post inoculation with either race. A second, large increase in PAL activity was observed only in the incompatible interaction (cv. Daliak inoculated with race 1), increasing 18-fold between 8 and 48 h post inoculation. Peroxidase activity in cv. Daliak increased rapidly within 2 h post inoculation with either race but was significantly higher in the incompatible interaction. Peroxidase activity in cv. Woogenellup increased by 4 h post inoculation with either race, but was significantly lower than that in cv. Daliak. Subsequent increases in peroxidase activity were recorded in both cultivars, however the levels remained constant in cv. Daliak infected with race 1, while activities in the other race-cultivar combinations decreased to control levels. It is hypothesised that the peak of activity of PAL at 48 h, and the rapid increase in peroxidase at 2 h are related to the race-specific resistance response of cv. Daliak to race 1 of K. caulivora, and that minor peaks of activity in the compatible interactions are general defence responses.