Formulation of biofungicides based on Streptomyces caeruleatus strain ZL-2 spores and efficacy against Rhizoctonia solani damping-off of tomato seedlings.

This work aims at exploring an antagonistic actinobacterial strain isolated from the roots of Ziziphus lotus in bioformulation processes and the biocontrol of Rhizoctonia solani damping-off of tomato seedlings. The strain Streptomyces caeruleatus ZL-2 was investigated for the principal in vitro biocontrol mechanisms and then formulated in three different biofungicides: wettable talcum powder (WTP), sodium alginate propagules (SAP) and clay sodium alginate propagules (CAP). Compared to a marketed control products (Serenade® and Acil 060FS®), the formulated biofungicides were investigated against the R. solani damping-off of tomato cv. Aïcha seedlings. The strain ZL-2 produced chitinases, cellulases, β-1,3-glucanases, cyanhydric acid and siderophores. It also showed strong antagonistic effect on the mycelial growth of R. solani. Bioautographic and HPLC analysis revealed the production of a single or several co-migrating antifungal compounds. The biofungicide WTP presented an attractive biocontrol effect by significantly reducing the disease severity index (DSI) compared to untreated seeds. No significant differences were obtained compared to the chemical treatment with Acil 060FS®. The viability of spores and biocontrol efficacy of the WTP were confirmed after 1-year storage. Strain ZL-2 has never been reported in the bioformulation of active biofungicides against Rhizoctonia solani damping-off and this work opens up very attractive prospects in the fields of biocontrol and crop improvement.