Contribution à la mise au point d'une méthode de lutte biologique contre la maladie des pourritures de la couronne de la banane
The antagonist activity of two yeast strains (Pichia anómala K strain and Candida oleophila O strain) against the parasitic complex responsible for crowns rot of banana has been evaluated. Their efficiency has been tested on three separated fungi: Colletotrichum musae, Fusarïum moiliforme, Cephalosporium sp. and on a parasitic complex formed by the association of these three fungi. Antagonist effects have been observed both on the two first fungi and on the complex. Strain O added at 108 ufc/ml on crowns which were previously inoculated with the complex showed the highest protection (56,0 %). This protection was superior to those observed against the fungi inoculated separately. The influence of the time between the addition of the O strain (10" ufc/ml) and the inoculation of the pathogens on the level of protection has also been measured. It appeared that protection by the O strain was remarkably reinforced when the strain was added 24 hours before the complex (57,0 %). This, in comparison with the additions performed 15 minutes or 3 hours after the pathogens inoculation. The utilisation of the O strain at 108 ufc/ml has been combined with the utilisation o f 50um polybags. These latter allow the formation of a modified atmosphere during the length of the bunches transfer. The protection level was at 61,0% when both methods were combined whereas protection by the yeast alone was o f 41,0%. A strict correlation between the severity of the symptoms and the protection by the yeast has been highlighted. When the severity of the disease increases, protection by the yeast decreases.