Functional Diversity of Royal Poinciana Rhizosphere Streptomyces with Antagonistic Activity against Neoscytalidium Stem Canker

Rhizosphere-associated actinobacteria represent an important component of microbial diversity and are a promising source of environmentally compatible agents for plant disease management. Royal poinciana (Delonix regia) is affected by stem canker caused by Neoscytalidium dimidiatum, a destructive fungal pathogen in warm regions. This study explored the functional diversity of streptomycete isolates associated with royal poinciana rhizosphere soils and assessed their potential contribution to biological suppression of stem canker.

Methods:
Actinobacterial isolates were recovered from rhizosphere soil and screened for antagonistic activity against N. dimidiatum. Promising isolates were identified as Streptomyces spp. and examined for antifungal mechanisms, including antibiosis and production of cell-wall-degrading enzymes. Selected isolates were further assessed using detached fruit assays and greenhouse trials on royal poinciana seedlings to determine their ability to reduce pathogen-associated symptoms.

Results:
A subset of streptomycete isolates showed clear antagonistic activity against N. dimidiatum under laboratory conditions. Among them, Streptomyces antibioticus UAE1 displayed the most consistent suppressive potential, combining antifungal metabolite activity with enzymatic degradation of fungal cell-wall components. This isolate reduced lesion development in detached fruit assays and limited disease development on royal poinciana seedlings when applied before pathogen challenge.

Conclusions:
The findings highlight royal poinciana rhizosphere soils as a valuable reservoir of beneficial streptomycetes with plant-protective functions. S. antibioticus UAE1 is a promising microbial candidate for further development as part of sustainable stem canker management. The study also supports the relevance of microbial diversity studies for discovering practical biocontrol resources in urban and ornamental plant systems.