Bacillus velezensis strain shows strong potential to control postharvest sweet potato black rot

Researchers have identified Bacillus velezensis L33a as a promising biological control agent against postharvest black rot of sweet potato, a major storage disease caused by the fungal pathogen Ceratocystis fimbriata.

The disease is responsible for substantial postharvest losses worldwide, highlighting the need for sustainable alternatives to conventional chemical fungicides.

Laboratory assays showed that strain L33a inhibited fungal mycelial growth by 82.83%, demonstrating strong antifungal activity. Fluorescence staining and scanning electron microscopy further revealed that the bacterium disrupts fungal cell membrane integrity and causes severe deformation of the pathogen's hyphae.

Beyond direct inhibition, the study demonstrated that volatile organic compounds (VOCs) released by Bacillus velezensis L33a play a major role in disease suppression. These volatile compounds reduced pathogen growth by 77.78%, outperforming the cell-free culture supernatant.

Among the identified VOCs, phenylethanol and octanoic acid completely prevented spore germination, achieving 100% inhibition of Ceratocystis fimbriata.

Experiments conducted on sweet potato tubers confirmed that both the bacterial culture and its volatile compounds significantly reduced lesion development during storage.

Gene expression analyses also demonstrated that L33a enhances the plant's natural defence responses by activating defence-related genes, particularly those involved in the jasmonic acid (JA) signalling pathway, which plays a central role in resistance against fungal pathogens.

According to the authors, Bacillus velezensis L33a combines multiple modes of action, including direct antifungal activity, suppression of spore germination, modulation of pathogen gene expression and activation of host defence mechanisms, making it a highly promising natural solution for sustainable postharvest disease management in sweet potatoes.

Source

Jian, W., Li, Y., Zhu, Y., Yao, Q., Qin, Y., Liu, H., Zhang, J., Qiu, G., Gui, Q., & Zhao, Z. (2026). Biocontrol Efficacy and Mechanism of Action of Bacillus velezensis L33a Against Postharvest Sweet Potato Black Rot. Journal of Fungi, 12(7), 492. https://www.mdpi.com/2309-608X/12/7/492