Abstract:

Citrus fruits are susceptible to postharvest decays caused by various pathogenic fungal disease agents. Citrus sour rot, caused by Geotrichum citri-aurantii is one of the most important postharvest diseases of citrus fruits Although synthetic fungicides are commonly used to combat the disease, ineffectiveness of these applications as well as their harmful effects on human health and the environment have been reported in many studies recently. Biological control of postharvest diseases utilizing antagonistic bacteria has been explored in different host plant-pathogen interactions as a promising alternative to synthetic fungicides. In this study, biocontrol potentials of endophytic bacterial isolates, obtained from fruits, branch and leaves of healthy citrus trees, were investigated against Geotrichum citri-aurantii on petri plates (in vitro) and fruit tests (semi in vivo conditions). Among the 24 putative endophytic bacterial isolates isolated, sixteen different antagonist bacterial isolates were selected and assessed against mycelial growth inhibition of G. citri-aurantii in vitro studies. Among the bacterial isolates tested, Bacillus spp. isolates significantly inhibited mycelial growth of fungal agent by 59.5-78.6%. The highest mycelial growth inhibition was caused by B. subtilis CM8 (78.6%). Bacterial isolates of Acinetobacter johnsonii CT7, Erwinia herbicola CM5, Pseudomonas putida CL2, Pantoea agglomerans CM14, Acinetobacter lwoffii CP1 and Stenotrophomonas maltophilia CP3 failed to inhibit mycelial growth in dual culture assays. Antagonistic activities of bacterial isolates increased by the pre-incubation time before fungal inoculation. Bacterial isolates of Bacillus spp. caused considerably morphological changes such as vacuolation, shrivelling, swelling and lysis of hyphae close to inhibition zone. On artificially inoculated fruits, isolates of Bacillus spp. also found to suppressed disease incidence significantly by 56.7-83.3%. Due to strong antagonistic activities, isolates of Bacillus spp, tested in this study have the potential to be used as biofungicide for controlling post-harvest disease agent(s) of citrus fruits.

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