Effects of different biocontrol bacteria treatments on the plant quality and rhizosphere soil microorganisms of Verticillium wilt-infested alfalfa plants

Alfalfa (Medicago sativa L.) Verticillium wilt is a class A quarantined disease in China. In September 2022, symptoms of this disease were observed in five-year-old alfalfa plants in a biocontrol field. This study aimed to assess the effects of the Verticillium wilt pathogen on alfalfa rhizosphere soil and plants under different biocontrol bacteria treatments using Bacillus amyloliquefaciens LYZ0069 and Streptomyces kanamyceticus LYZ0133.

The pathogen responsible for Verticillium wilt in alfalfa was identified through molecular biology techniques and morphological examination. High-throughput sequencing was used to profile the bacterial and fungal communities in the rhizosphere soil of infected and healthy alfalfa plants under different biocontrol treatments. Culturable bacteria were isolated and evaluated for their inhibitory effects on the pathogen. Additionally, the physicochemical properties of rhizosphere soil and the nutrient content of plants were measured.

The pathogen was identified as Verticillium alfalfae. In total, 28 bacterial species and 11 fungal species were isolated from the rhizosphere soil. Pseudomonas species exhibited significantly higher isolation and inhibitory rates compared to other bacterial strains. Infection by V. alfalfae significantly affected the Pieloue evenness index of bacteria and the ammonium nitrogen content in the rhizosphere soil. The interactions between biocontrol bacteria and V. alfalfae significantly impacted alfalfa plant quality.

Alfalfa Verticillium wilt was detected in central of Gansu Province, significantly influencing plant nutrient content and relative abundance of Pseudomonas in alfalfa rhizosphere soil.