Assessment on the Effect of Formulative Materials on the Viability and Efficacy of Serratia marcescens-a Biocontrol Agent Against Fusarium oxysporum F. sp. cubense race 4

Problem statement: Application of biocontrol agents to the field in pre-existing free-cell forms often results in poor cell viability which subsequently affects their efficacy in suppressing pathogen development. There is therefore a need to bioformulate these biocontrol agents not just to enhance their field potential, but for easy storage, delivery and application as well. Approach: In this study, the bioformulations for a biocontrol bacterium Serratia marcescens, was developed using bentonite clay as carrier material with various combinations of enrichment and additive materials. The most suitable bioformulation was determined by assessing the compatibility of the formulative materials in preserving cell viability during storage, the resulting appearance of the bioformulation, the protection confered to cells upon sunlight exposure and the efficacy of the formulated cells (with and without sunlight exposure) in inhibiting the growth of the pathogenic Fusarium oxysporum F. sp. cubense race 4 (FocR4). Results: Bioformulation benefited the cells when exposed to sunlight (UV rays). The benefits of bioformulation were attributed to the carrier material (bentonite clay) and the enhancement materials (NFSM and sucrose). They confer UV-protectant effects as well as providing nutrient source for the formulated cells. The additive material PABA was observed to have antimicrobial effect on the formulated cells. Formulative materials however has no impact on the efficacy of the cells in inhibiting FocR4 as no significant differences in percentages of FocR4 inhibition were observed between bioformulations with and without exposure to sunlight. Conclusion: Present study observed that incorporation of sucrose into Bentonite (BS) has the most potential for large-scale testing as it showed good viability and efficacy results.