Sodium Humate as a Promising Coating Material for Microencapsulation of Beauveria bassiana Conidia Through Spray Drying

Abstract

Microencapsulation of Beauveria bassiana (Bb) conidia with sodium humate (SH) was undertaken successfully through spray drying at a high inlet air temperature of 175°C with corresponding outlet air temperature of 86.5 ± 1.3°C using 0.2% SH. The obtained product was a free-flowing, dark-brown powder containing microcapsules of Bb conidia coated with sodium humate (Bb-SH). These microcapsules measured 2.47–3.57 µm and possessed an uneven, fluffy surface. The colony-forming units (CFU) of Bb-SH microcapsules spray-dried at 175°C were 21.54 LCFUg⁻¹, on par with 21.59 LCFUg⁻¹ for Bb conidial powder not subjected to spray drying. Bb-SH microcapsules resulted in a high mortality of 93.0% against six-day-old Helicoverpa armigera larvae within five days after treatment. Bb-SH microcapsules readily dispersed in water, releasing sodium humate from the conidial surface. Germination of conidia was not affected by sodium humate as visualized by scanning electron microscopy of the cuticular surface of treated larvae. Bb-SH microcapsules showed good viability (21.11 LCFUg⁻¹) at the end of six months of storage at room temperature (∼30°). Thus, sodium humate is a promising biopolymer for encapsulation of Bb conidia for extended shelf-life at room temperature.

Keywords:

• Beauveria bassiana
• Helicoverpa armigera
• Microencapsulation
• Sodium humate
• Spray drying

ACKNOWLEDGMENTS

The authors thank the Project Director Dr. K. S. Varaprasad and Dr. Harvir Singh, Head, Crop Protection, for providing the facilities for carrying out the work.

Notes

*Starting spore count was 21.18 LCFU = log₁₀ CFU 0.5 g⁻¹.

*Values in parenthesis are angular transformed.

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