Isolation and Characterization of a New Lytic Phage MA9V-2 Against Chryseobacterium indologenes MA9 and Its Combined Application with MA9V-1 for the Control of Panax notoginseng Root Rot

Panax notoginseng, a valuable medicinal plant in Yunnan, suffers significant yield losses due to root rot, with Chryseobacterium indologenes MA9 as a major causal agent. Conventional chemical control methods are limited by residues and the development of bacterial resistance, underscoring the need for alternative strategies. In this study, we isolated a new lytic myovirus, vB_CinP_MA9V-2, from wastewater using MA9 as the host. MA9V-2 exhibited high lytic efficiency with 75% adsorption in 25 min and a burst size of ~100 PFU per cell, stability across pH 4 to 11 and temperatures of 4 to 50 °C, a moderately broad host range, and effective suppression of biofilm formation. Genome analysis confirmed the absence of virulence or antibiotic resistance genes, indicating its safety for application. In potted plant experiments, single-phage treatment reduced root rot incidence to 16.7% compared with 83.3% in the control, while a combined treatment with phages achieved up to 80 percent control. Curative effects post-infection were limited with a disease incidence of 61.3%, highlighting the preventive advantage of phage therapy. Overall, these results demonstrate that phage therapy, particularly using a combination of phages, shows potential for application in the management of bacterial root rot in P. notoginseng.