Role of Phenolic Metabolism in the Defense of the Olive-tree against Leaf-spot Disease Caused by Spilocaea oleagina.

In order to study the role of phenolic metabolism in the defense of the olive-tree against Spilocaea oleagina, three defense components: soluble phenols, parietal phenols, lignin and phenylalanine ammonia-lyase (PAL), were studied in two different varieties: a resistant (Picholine du Languedoc) and a susceptible (Moroccan Picholine). The inoculation of olive-tree leaves by Spilocaea oleagina induces a foliar necrosis whose speed of onset and expansion distinguishes clearly the two studied varieties according to their behaviour to the leaf-spot disease. For the resistant variety, these symptoms are composed of small necrotic lesions, whereas for the susceptible variety, they appear as extended necrotic spots. These symptoms are accompanied by an increase in the accumulation of the contents of soluble and parietal phenols, the intensification of the lignification and the induction of the PAL activity of which the speed and intensity plainly distinguish both varieties under study. These results reveal that the response of phenolic metabolism to the resistance of the olive tree to the leaf-spot disease appears to occur in the early stages of infection leading to an increase in the biosynthesis of the contents of three defense components (soluble phenols, parietal phenols and lignin). [ABSTRACT FROM AUTHOR]