Antifungal activity of Tagetes patula extracts on some phytopathogenic fungi: ultrastructural evidence on Pythium ultimum.

Methanol extract, obtained from Tagetes patula plant, was assayed against three phytopathogenic fungi: Botrytis cinerea, Fusarium moniliforme and Pythium ultimum. The antifungal activity was tested both in the dark and in the light, using two different lighting systems. The data showed that the extract proved to have a dose-dependent activity on all the fungi with a marked difference between treatments in the light than in the dark. Good growth inhibition was observed in fungi only when these were treated with the highest dose of the extract and irradiated, whereas the same dose gave only a modest inhibition when the experiment was conducted in the dark. At 5 and 10 microg/ml in the dark, growth increased. The results indicated that the presence of a luminous source enhances the antifungal activity, with small differences between UV-A and solar spectrum light. SEM and TEM observations on Pythium ultimum revealed that the Tagetes patula extract induced alterations on cell fungal membranes with a photoactivation mechanism possibly involving the production of free radicals and leading to a premature aging of the mycelium.