Synergistic interactions in designed bacterial consortia: Dual effects on control rusty root rot and growth promotion...

Ginseng rusty root rot, caused by Ilyonectria robusta, is the most severe soil-borne disease affecting ginseng cultivation. A synthetic microbial community (SynCom) was developed for the first time using antagonistic and growth-promoting endophytic and rhizosphere bacterial strains to control ginseng rusty root rot, and its synergistic mechanisms had been clarified. The 89 out of 98 biocontrol bacterial groups exhibited synergistic inhibitory effects against I. robusta, while 40 consortia showed both growth-promoting and synergistic effects. Among these, the 24 consortia inhibited mycelial growth of I. robusta by more than 80%, and seven consortia suppressed spore growth by over 60%. The inhibition rates were increased by 19%-131% and 5%-137%, respectively, compared with single strain treatment. The biocontrol consortia achieved superior control efficacy against ginseng rusty root rot in the field, which six consortia exhibited control efficacy exceeding 50%, with the consortium CL95 showing the highest efficacy at 66.67% and significantly promoted ginseng growth. The content of I. robusta in ginseng roots decreased by 46.97% following CL95 treatment compared to the single-strain NJ13. Mechanistic studies indicated that the colonization efficiency of the consortia in ginseng tissues and rhizosphere soil was significantly higher than that of single strains within 63 days. The colonization of CL95 in ginseng leaves, stems, epidermis, root core, lateral root, fibrous root and soil was 33%-215% higher than that of single strain NJ13, respectively. In addition, compared with NJ13, the four soil enzyme activities were increased by 100%-150%, and the expression levels of five defense enzyme genes in three different growth periods of ginseng were increased by 75%-167%, among which CL95 had the most obvious effect. It was also found that biocontrol consortia significantly increased the diversity of microbial communities and the abundance of beneficial fungi and bacteria in ginseng rhizosphere soil, while significantly reducing the abundance of pathogenic fungi. Correlation analysis showed that the consortia were significantly positively correlated with root weight and soil enzyme activity, promoting ginseng growth. This study lays a theoretical foundation for overcoming the limitations of single-strain biocontrol agents and highlight the potential for industrial application of biocontrol consortia in sustainable agriculture.