Evaluation of streptomycete actinobacterial isolates as biocontrol agents against royal poinciana stem canker disease caused by the fungal pathogen Neoscytalidium dimidiatum

•Forty-seven actinobacterial isolates were obtained from the UAE rhizosphere soils.•Three Streptomyces strains exhibited in vitro inhibition against N. dimidiatum.•S. antibioticus UAE1 possesses strong antibiosis and CWDEs activities in vitro.•S. antibioticus UAE1 restricted lesion development of N. dimidiatum on apple fruits.•S. antibioticus UAE1 suppressed disease symptoms on royal poinciana in the greenhouse. In this study, 47 actinobacterial isolates were obtained from rhizosphere soils of royal poinciana in the United Arab Emirates (UAE). Three Streptomyces strains exhibited powerful in vitro antifungal activity against Neoscytalidium dimidiatum (the causal agent of stem canker disease of royal poinciana). The antifungal action of Streptomyces rochei UAE2 and Streptomyces coelicoflavus UAE1 was mainly correlated with antibiosis and cell-wall-degrading enzymes production, respectively. Streptomyces antibioticus UAE1 was, however, associated with both mode of actions. These isolates suppressed lesion development on fruits inoculated with N. dimidiatum in the apple fruit bioassay. Under greenhouse conditions, individual biocontrol agents (BCAs) showed greater efficacies against stem canker when applied before N. dimidiatum than after the pathogen. The curative effects of Cidely® Top (a chemical fungicide) and S. antibioticus UAE1 on disease symptoms were comparable on royal poinciana. Prior to pathogen inoculation, S. antibioticus UAE1 was capable to suppress disease symptoms and prevent the pathogen spread, suggesting a relative superiority of S. antibioticus UAE1 over all other tested treatments. This was evident in the significant (P