PHENOLICS AND ENZYMATIC ACTIVITY ASSOCIATED WITH DAMAGE CAUSED BY POWDERY MILDEW ON PEACH LEAVES

Abstract

A possible association between phenolic compounds and enzymes with the susceptibility of peach (Prunus persica (L.) Batsch) to powdery mildew (Sphaerotheca pannosa (Wallr.) Lev. var. persicae Wor.) was investigated in the greenhouse in August 1998 and in the autumn of 1999. The variables evaluated were degree of susceptibility to powdery mildew, latent period of infection, the final infection, the concentration of total phenolics and the activity of the enzymes: polyphenoloxidase and phenylalanine ammonia-lyase. Metabolism phenolics like strategy of defense of the peach when attacked by powdery mildew are a complicated matter. Phenolic concentration and the activity of the enzymes phenylalanine ammonia-lyase (PAL) and polyphenoloxidase (PPO) increased after inoculation in all of the evaluated peach genotypes, but only during the first 24 h. In this case the genotypes with a zero susceptibility index presented increased enzymatic activity. A negative correlation between the susceptibility to powdery mildew and the other variables was observed 24 h after inoculation: their respective correlation coefficients were total phenolics, -0.6059, PAL, -0.4938 and PPO, -0.6476. Perhaps participation of phenolics, PAL and PPO in peach defense mechanism after attack of powdery mildew, occurs mostly in the first 24 h after inoculation, for impede the establishment of the fungus, mainly in the tolerant genotypes. Powdery mildew latency period on peach leaves, differs according to their susceptibility index; when the index decrease, the period of latency increased.