Effect of capsulated Bacillus velezensis with alginate on plant growth indexes and improve of resistance under Rhizoctonia solani -stress in tomato

Document Type : Research Paper

Authors

• Abdolhossein Taheri ¹
• Seyed Javad Sanei ¹
• Elahe Lotfalinezhad ²
• Amin Radmard ²

¹ Department of Plant Protection, Faculty of plant production, Gorgan University of Agricultural sciences and Natural Resources, Gorgan , Iran

² PhD graduate in Plant Pathology, Department of Plant Protection, Faculty of plant production, Gorgan University of Agricultural sciences and Natural Resources, Gorgan , Iran

Abstract

Keywords

• Induced resistance
• Growth promotion
• Bacillus velezensis
• Capsule formulation
• Rhizoctonia solani

Extended Abstract

Introduction

Tomato crops are severely affected by soilborne pathogens like Rhizoctonia solani, which causes extensive losses through damping-off and root rot diseases. Since traditional fungicide applications have limited success and are environmentally risky, biological control using plant growth-promoting rhizobacteria (PGPR), especially Bacillus species, offers an environmentally friendly alternative. These beneficial bacteria combat pathogens through the production of antimicrobial substances, competition for nutrients, and plant growth stimulation. However, PGPR are faced with survival challenges in field conditions due to environmental stresses like temperature, pH, moisture, and competitive microorganisms. Ionically gelated encapsulation technology using biocompatible polymers like sodium alginate is a new strategy that entraps microorganisms in biodegradable capsules, thereby providing controlled release, improving soil establishment, extending shelf life, reducing application frequency, and being environmentally compatible.

Materials and Methods

Firstly, B. velezensis isolate and R. solani pathogen fungus were obtained from Gorgan University of Agricultural Sciences and Natural Resources' fungal collection in the Plant Pathology Department. Encapsulated and non-encapsulated B. velezensis inhibitory capacity against R. solani were tested through dual culture, volatile compound, and non-volatile compound tests in PDA medium according to completely randomized design with four replications. Encapsulated B. velezensis was thereafter prepared using ionic gelation method with 2% sodium alginate and 0.1 M calcium chloride solution, and capsule morphology, size, and encapsulation efficiency were determined. The shelf life of bacterial in 5, 25, and 35°C temperatures for 15 days was evaluated in encapsulated versus non-encapsulated form. Greenhouse experiments were performed to evaluate the ability of these formulations to control R. solani damping-off disease with a growth period of 30 days in tomatoes using a factorial experiment based on a completely randomized design with 4 replications. The factors that were studied were: 1- Treatments (encapsulated B. velezensis, non-encapsulated B. velezensis, and sodium alginate capsules without bacteria as control), 2- Various concentrations of bacterial treatments (1×10³, 5×10³, and 10⁴ CFU/g for encapsulated and CFU/ml for non-encapsulated forms), and 3- Temperature storage conditions (5, 25, and 35°C). Plant growth parameters, disease incidence, and antioxidant activity were measured following standard protocols, and data were calculated using R.4.2.2 software with Duncan's multiple range test at p≤0.05 level of significance.

Results

Encapsulated B. velezensis capsules through ionic gelation method exhibited approximate spherical shape having wet capsules size 2600 micrometers in diameter (transparent white) and dried capsules size 1000 micrometers (yellow, wrinkled surface). Encapsulation efficiency was 99%. Encapsulation also enhanced the survival and stability of B. velezensis at 25°C and 35°C compared to the non-encapsulated form with 5°C being the optimal storage condition for long term. No protective difference was observed among dry and wet capsules against temperature changes. Greenhouse experiments confirmed encapsulated B. velezensis formulation suppressed disease incidence in comparison to non-capsulated B. velezensis and bacterial-free capsules. Encapsulated B. velezensis treated plants exhibited considerable improvement of growth indices compared to control groups with only root height found to be significantly affected by formulation type. The findings substantiate the positive and effective role of encapsulated B. velezensis towards seedling mortality reduction and tomato growth promotion, validating its efficacy as an effective alternative to enhance reduction of chemical pesticide dependency.

Conclusion

The findings of this research indicate that the application of encapsulated formulation significantly improves the persistence and viability of B. velezensis compared to the non-encapsulated one, and can also lead to the promotion of its inhibitory ability. Therefore, the obtained results are of great significance regarding the practical application of microbial fungicides based on encapsulated formulation and provide a clear vision for the application of encapsulated B. velezensis as a promising alternative to reducing the application of chemical pesticides.

Author Contributions

Conceptualization, A. Taheri and S.J. Sanei; methodology, S.J. Sanei and E. Lotfalinezhad; Research & Investigation, A. Taheri, S.J. Sanei, E. Lotfalinezhad and A. Radmard; software, S.J. Sanei and E. Lotfalinezhad; writing—original draft preparation, S.J. Sanei and E. Lotfalinezhad; writing—review and editing, A. Taheri, S.J. Sanei, E. Lotfalinezhad and A. Radmard; All authors have read and agreed to the published version of the manuscript. A. Taheri is supervisor and S.J. Sanei is advisor of the project. All authors contributed equally to the conceptualization of the article and writing of the original and subsequent drafts.    

Data availability statement

Data generated or analyzed during this study are provided in full within the published article.

Ethical considerations

All research followed ethical guidelines to minimize harm to insects and avoid disruption of natural habitats. Sampling was limited to the minimum necessary, and no endangered or protected species were collected. All activities complied with relevant regulations, and data were recorded and reported with integrity.

Conflicts of Interest

The authors declare that they have no conflicts of interest