Biocontrol of Fusarium mangiferae responsible for mango malformation using bacterial isolates

Fusarium species are known to be responsible for mango malformation, a serious pre-harvest disease causing major yield and financial losses to the industry worldwide. This study confirmed the identity and pathogenicity of the species associated with the disease in the northern provinces of South Africa. Thirty-five fungal isolates were obtained from infected orchards, of which 32 were identified as the malformation pathogen Fusarium mangiferae. Seventy-seven bacterial isolates, obtained from mango orchards as well as unrelated environments, were screened for their antifungal properties and the modes of action of the best isolates against Fusarium were established. The study demonstrated that only five bacterial isolates (Alcagenes faecalis) were able to significantly inhibit the growth of the pathogen. The modes of action of the bacteria were a combination of competition for space and secondary metabolites produced by the bacteria, which included volatiles, phenolic compounds and siderophores. An in vivo trial was performed to determine if exposure to the pathogen and antagonist could induce resistance by increasing secondary metabolites and specifically mangiferin. Chemometric analysis of the data obtained from the in vivo trial revealed that the total soluble secondary metabolite concentrations after application of the selected biocontrol agents or pathogen inoculation, were lower when compared to the control group.