In vivo and in vitro antagonism of Streptomyces sp. RO3 against Penicillium digitatum and Geotrichum candidum

Abstract

Streptomyces strains may control postharvest lemon fruit diseases caused by Penicillium digitatum and Geotrichum candidum. Four Streptomyces strains (RO3, MC3, Alem and CE1) were tested and RO3 was the strain with the highest antagonistic activity. Streptomyces RO3 showed a maximum biomass value (2.15 g/L) after 72 h incubation in yeast extract, malt extract, glucose (YMG) medium; in starch casein medium the highest value was 0.477 g/L at 120 h incubation. The metabolites produced in YMG medium showed the maximum inhibition against G. candidum and P. digitatum (19.64 and 62.12% respectively). The inhibitory activity of metabolites decreased after autoclaving. RO3 metabolites have molecular mass higher than 2000 and they have fungicidal action mode against P. digitatum. In vivo assays, RO3 metabolites with wax, totally controlled lemon diseases (mainly sour rot and green mold). This is the first study on Streptomyces to control postharvest lemon diseases.