Isolation and Identification of Phages Infecting the Pathogen MA9 of Panax notoginseng and Study on the Biocontrol of Root Rot Disease

Qian Zhou¹He Zou²Jinmei Chai¹Yunlin Wei^1*

• ¹Kunming University of Science and Technology School of Environmental Science and Engineering, Kunming, China
• ²Sichuan University of Science and Engineering School of Bioengineering, Zigong, China

Panax notoginseng, a valuable medicinal plant in Yunnan, suffers significant yield loss due to root rot disease. Among the various pathogens responsible for this disease, the contribution of bacteria—particularly Chryseobacterium indologenes MA9—has long been underestimated. Given the drawbacks of conventional chemical control, such as drug residues and resistance, this study pioneers the use of phages to manage bacterial root rot in P. notoginseng. Pathogenicity tests confirmed MA9 as a highly virulent strain, causing up to 80% disease incidence in vivo. A novel myovirus, vB_CinP_MA9V-2 (MA9V-2), was isolated using MA9 as host from wastewater. It demonstrated high lytic efficiency (75% adsorption within 25 min, burst size ~6 PFU/cell), stability across pH 4–10 and 4–60°C, and broad antibacterial spectrum. MA9V-2 also suppressed biofilm formation, reducing bacterial virulence. Whole-genome analysis revealed MA9V-2 as a potentially novel phage lineage devoid of virulence or resistance genes, indicating safety for application. The biocontrol experiments demonstrated that phage treatment significantly reduced the incidence of root rot disease. In the potted plant prevention group, the application of a single phage reduced the disease incidence to 16.7%, compared to 83.33% in the control. Notably, the combined use of phages MA9V-1 and MA9V-2 further enhanced the biocontrol efficacy, achieving a control rate of up to 80%. However, curative effects were limited post-infection (disease rate reduced only to 61.3%), highlighting prevention as the preferred strategy. Therefore, phages—particularly combination therapies—exhibited remarkable preventive effects against root rot in P. notoginseng. This study provides a novel approach for the biocontrol of bacterial diseases in plants.