Potential of bacterial isolates for the biological control of apple scab (Venturia inaequalis)

Apple scab, caused by Venturia inaequalis , is one of the most important diseases in apple orchards generally controlled by chemical fungicides. In order to promote sustainable practices, these fungicides should be replaced with environmentally friendly alternatives, such as biological control methods. This study tested the biocontrol potential of nine bacterial isolates against five isolates of V. inaequalis from the Fes-Meknes region. These bacterial isolates had previously demonstrated activity against other infections. These bacterial isolates exhibited a mycelial growth suppression ranging from 60 to 92%, with significant differences observed among the fungal isolates. In detached leaf bioassays, the antagonistic bacterial strains showed greater preventive than curative efficacy in combination with the fungicide difenoconazole. In vitro and in vivo treatments showed variable efficacy depending on the fungal isolates. Among the microorganisms tested, Alcaligenes faecalis (ACBC1), Bacillus amyloliquefaciens (CPa2), and B. amyloliquefaciens (SF14) proved effective against several strains of V. inaequalis , although their effectiveness was generally lower than that of the fungicidal product (difenoconazole). In vitro tests using culture filtrates of the aforementioned bacterial isolates gave inhibition rates of 21 to 73%. In addition, inhibition rates ranging from 40 to 50% reflected the importance of the antifungal metabolites produced by these bacterial isolates on spore germination and elongation. The bacteria also emitted volatile compounds, which exhibited antifungal activity, inhibiting fungal growth between 6 and 80%. Additionally, biochemical studies confirmed that these antagonist bacterial isolates have the potential to secrete lytic enzymes, thus adding to their antifungal properties. These findings suggest that these bacterial strains hold great potential for the development of effective biofungicides in sustainable and efficient management of apple scab.