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Preparation and evaluation of Bacillus megaterium-alginate microcapsules for control of rice sheath blight disease
R Wiwattanapatapee1, A Chumthong, A Pengnoo
1Department of Pharmaceutical Technology, Faculty of Pharmaceutical Sciences, Prince of Songkla University, Hat Yai, Songkhla 90112, Thailand.
Abstract:
Bacillus megaterium encapsulated in calcium alginate microcapsules was prepared and tested for its efficacy against sheath blight disease of rice. In laboratory conditions, the aqueous suspension (1:100, v/v in potato dextrose agar) of the bacterial microcapsules (10(10) spores/ml) inhibited mycelial growth of Rhizoctonia solani (>99 %) after the microcapsules were produced and stored for 12 months at room temperature (28 ± 2 °C). The survival of the bacterium in the microcapsules in response to ultraviolet (u.v.) irradiation and high temperature was investigated. The survivability of the bacterium in the encapsulated form was greater than that of the fresh cells when it was subjected to u.v. (20-W General electric u.v. lamp from a 25 cm distance for 48 h) and a high temperature treatment (80 °C for 48 h). Cells of the bacterium were detected by scanning electron microscope on both the leaf sheath and the leaf blade (in pot tests in a greenhouse) after spraying encapsulated product. The number of bacteria on the surface of both rice tissues (5 Log. number/g of plant) after spraying with encapsulated product was not significantly different from that after spraying with fresh cells onto the rice seedlings. Spraying the encapsulated B. megaterium on rice plants in the greenhouse was as effective as spraying a chemical fungicide for suppressing rice sheath blight disease.
Insights
Encapsulated Bacillus megaterium in alginate microcapsules effectively controlled rice sheath blight for 12 months. This biocontrol agent demonstrated enhanced survival against UV and heat, matching fungicide efficacy.
Area of Science:
- Agricultural Microbiology
- Plant Pathology
- Biotechnology
Background:
- Rice sheath blight, caused by Rhizoctonia solani, is a major threat to rice production worldwide.
- Biological control agents offer a sustainable alternative to chemical fungicides.
- Bacillus megaterium is a known plant growth-promoting bacterium with potential biocontrol properties.
Purpose of the Study:
- To evaluate the efficacy of Bacillus megaterium encapsulated in calcium alginate microcapsules against rice sheath blight.
- To assess the stability and survival of encapsulated B. megaterium under storage and stress conditions.
- To compare the efficacy of encapsulated B. megaterium with chemical fungicides in greenhouse trials.
Main Methods:
- Calcium alginate microencapsulation of Bacillus megaterium spores.
- In vitro inhibition of Rhizoctonia solani mycelial growth by microcapsules.
- Assessment of bacterial survival under UV irradiation and high-temperature stress.
- Greenhouse pot tests evaluating disease suppression and bacterial colonization on rice plants.
- Comparison of encapsulated B. megaterium spray with chemical fungicide treatment.
Main Results:
- Microencapsulated B. megaterium inhibited >99% of Rhizoctonia solani mycelial growth after 12 months of storage at room temperature.
- Encapsulated B. megaterium showed significantly greater survival rates than fresh cells when exposed to UV irradiation and 80°C heat treatment.
- Scanning electron microscopy confirmed bacterial presence on rice leaf sheaths and blades after spraying.
- The number of bacteria on plant tissues was comparable between encapsulated and fresh cell applications.
- Spraying encapsulated B. megaterium effectively suppressed rice sheath blight, performing similarly to a chemical fungicide.
Conclusions:
- Alginate microencapsulation provides a stable and effective delivery system for Bacillus megaterium as a biocontrol agent for rice sheath blight.
- Encapsulation enhances the bacterium's survival under adverse environmental conditions, extending its viability and efficacy.
- Encapsulated Bacillus megaterium represents a promising biological alternative to chemical fungicides for sustainable management of rice sheath blight.
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