Bacillus cereus B8W8 an effective bacterial antagonist against major postharvest fungal pathogens of fruit

Abstract

The antifungal activity of Bacillus cereus (B8W8) was investigated against major post-harvest fungal pathogens affecting citrus and apples fruits namely Penicillium digitatum, Penicillium italicum, Geotrichum citri-aurantii, Penicillium expansum, Botrytis cinerea, Monilinia laxa and Monilinia fructigena. The in vitro dual culture of B8W8 and fungal pathogens showed high inhibition rates of the mycelial growth of Monilinia laxa and Penicillium digitatum (71.4% and 72.5% respectively). Subsequently, the volatile compounds (VOCs) have a high antagonistic effect against Monilinia laxa (86.4%) and Monilinia fructigena (73.4%). In addition, the bacterial-free cell filtrate of B8W8 had a significantly important effect on the inhibition of spore’s germination and mycelial growth of Penicillium expansum, Botrytis cinerea, Penicillium italicum and Geotrichum citri-aurantii. The in vivo bioassays revealed a significant impact of B8W8 on fruit decays either by reducing the disease severity of causative agents or by completely preventing their occurrence, particularly brown rot of apple caused by M. laxa and green mold of citrus caused by P. digitatum (DS = 0%). However, the severity of sour rot of citrus caused by G. citri-aurantii was only reduced by 50%. The semi-commercial trials showed a high potential of B. cereus B8W8 to reduce the incidence of gray mold of apple and green mold of citrus to very low values during at storage. In addition, the biological treatment with B8W8 was shown generally more effective than imazalil, the chemical treatment reference. Furthermore, the rapid colonization of fruit wounds by B8W8 could promote its antagonistic ability. Moreover, biochemical tests showed the ability of B8W8 to produce protease, amylase, and hydrocyanic acid (HCN). Interestingly, the molecular analysis demonstrated the ability of this bacterium to produce the fengycin. The secretion of this lipopeptide and lytic enzymes is more likely the major mechanism of action involved in the biocontrol activity of this bacterium. Results indicated that quality parameters of fruit, when challenged post-harvest pathogens and treated with B8W8, were mostly very close to those of the untreated control, suggesting that B8W8 did not affect the fruit quality. Accordingly, it was concluded that B. cereus strain B8W8 could be an effective biological agent to control the main fungal pathogens of apples and citrus fruits during post-harvest period.