Isolation, Identification, and Characterization of Endophytic Bacillus from Walnut (Juglans sigillata) Root and Its Biocontrol Effects on Walnut Anthracnose

Anthracnose is a major disease of walnut, which seriously reduces the yield and quality of walnut in Yunnan province. Therefore, it is necessary to explore and find a biological control agent for the prevention and control of anthracnose disease. In this study, an endophytic Bacillus WB1, with broad-spectrum antibacterial activity was isolated and screened from healthy walnut roots. The strain WB1 was identified as Bacillus siamensis WB1 based on morphological characteristics, physiological and biochemical tests, and 16S rRNA gene sequence analysis. Bacillus siamensis WB1 produces siderophores and indole-3-acetic acid and solubilizes inorganic phosphate. The strain WB1 not only showed a significant inhibition effect on fourteen phytopathogens, but also showed obvious inhibition on the spore germination of Colletotrichum acutatum. Meanwhile, strain WB1 can code genes for the production of antifungal lipopeptides and generate extracellular hydrolytic enzymes (protease, β-1, 3-glucanase, cellulase, and amylase). In addition, WB1 activated the systemic resistance of the host plant by enhancing the activity of defense enzymes, including phenylalanine ammonia lyase (PAL), peroxidase (POD), and polyphenol oxidase (PPO). The results of greenhouse assays also revealed that B. siamensis WB1 can effectively reduce the occurrence and severity of walnut anthracnose disease. These results also indicated that B. siamensis WB1 is a potential biocontrol agent for walnut anthracnose.