Grape Marc Compost Tea Suppressiveness to Plant Pathogenic Fungi: Role of Siderophores

Abstract

AbstractIt is important to know about the mechanisms that suppress plant diseases when compost from vegetable residues and/or their liquid extracts (compost tea) are used in order to improve the efficiency of this suppressing effect on pathogens. In this study, we assessed the presence of siderophores in various grape marc aerated compost teas (ACT) and their suppressing effect on nine pathogens: Rhizoctonia solani, Fusarium oxysporum f. sp. radicis-lycopersici, Fusarium oxysporum f. sp. lycopersici race 0, Fusarium oxysporum f. sp. lycopersici race 1, Fusarium oxysporum f. sp. radicis-cucumerinum, Verticillium dahliae, Pythium aphanidermatum, Phytophthora parasitica and the mycopathogen, Verticillium fungicola. Three concentrations (5, 10 and 15%) filtered, microfiltered and sterilized ACT were added to Petri dishes with a PDA medium, and 1 mM of ferric chloride (FeCy. After adding this mixture, a 0.5 cm disc was placed at the center of each dish containing the vegetative and reproductive body of each of the fungi to be tested. All the dishes were incubated at 25°C for seven days, except R. solani y P. aphanidermatum, which developed after 4 days. The addition of 1 mM of FeCl3 deactivated the siderophores present in the ACT, suppressing their inhibition of fungal development. The results obtained with the microfiltered ACT revealed that the microorganisms present in grape marc compost excreted siderophores into the medium which were responsible for inhibiting the growth of the 9 fungi tested. This activity was annulled by the addition of ferric chloride. The same results were achieved with the ACT obtained from filtering. This inhibition was not 100% after adding FeCl3 due to the fact that the microorganisms present in this tea, exhibited other biocontrol mechanisms.