Potential of Some Bacteria for Biological Control of Postharvest Citrus Green Mould Caused by Penicillium digitatum

Ten bacteria isolate (4 Bacillus subtilis, 2 Bacillus pumilus, 2 Bacillus cereus, 1 Bacillus megaterium, and 1 Agrobacterium radiobacter) were tested in vitro for antagonistic properties against Penicillium digitatum, the causal agent of citrus green mould. The effect of these bacteria was also observed on mycelial growth, spore germination, and spore production of the pathogenic fungus in broth culture. Extracellular enzyme activities of the bacteria were determined. According to the results of in vitro antagonistic tests and enzymes activities, the most promising bacteria were Bacillus subtilis and Agrobacterium radiobacter. These bacteria were tested for disease suppression on lemon fruits. In addition, these bacterial isolates also showed remarkable antifungal activity against the pathogen on lemon fruits. The results of this study showed that Bacillus subtilis and Agrobacterium radiobacter showed remarkable antifungal activity against the pathogen. Chitinase and glucanase enzyme activity of all the tested bacteria was positive. Protease enzyme activity was positive in all tested bacteria with the exception of Agrobacterium radiobacter. In addition, all bacteria inhibited mycelial growth and spore germination (except Agrobacterium radiobacter) of the fungus. Bacillus subtilis, Bacillus cereus, and Agrobacterium radiobacter inhibited spore production in broth culture. Bacillus subtilis and Agrobacterium radiobacter were tested on lemon fruits significantly reduced disease severity. Consequently, these isolates can be used as new biocontrol agents in controlling the post-harvest decay of citrus fruits caused by Penicillium digitatum.