Efficacy of indigenous bacterial antagonists from the anthosphere of Macadamia integrifolia in controlling Cladosporium raceme blight.

Floral diseases of macadamia, such as raceme blight, are among the main limiting factors for crop production, and the low availability of registered products for phytosanitary management further aggravates this challenge. In this context, biocontrol agents emerge as a sustainable and effective alternative for integrated disease management. This study aimed to select antagonistic bacteria for the control of raceme blight in macadamia, caused by Cladosporium xanthochromaticum. For this purpose, bacteria were isolated from macadamia racemes, identified, and tested against the phytopathogen in both in vitro and in vivo experiments (racemes and field plants). Their mechanisms of action and compatibility with pesticides registered for the crop were also evaluated. Strains of Serratia ureilytica and Bacillus subtilis proved effective in controlling the disease in the field. S. ureilytica reduced the incidence of C. xanthochromaticum by 27.04% to 35.38% and its sporulation by 52.04% to 52.65%. Meanwhile, B. subtilis was effective in reducing sporulation in racemes by 16.25% to 26.08%. Both strains demonstrated inhibitory activity through volatile and non-volatile compounds, as well as competition for nutrients. The strains were compatible with all pesticides tested, except copper hydroxide, to which S. ureilytica was sensitive. The results indicate that the selected strains can be incorporated into the integrated disease management of macadamia, contributing to the reduced reliance on chemical pesticides.