A combination of Streptomyces and Bacillus strains enhances the biocontrol efficacy against phytopathogenic diseases caused by Sclerotinia, Rhizoctonia, and Fusarium.

Biotic stress reduces crop quality and yield, adversely affecting agricultural and forestry production and ecosystems. Plant-beneficial endophytes offer a promising approach to mitigating such stress. This study developed a novel multi-strain biocontrol agent comprising Streptomyces dioscori SF1 and Bacillus cereus G2, designated as SF1+G2. SF1+G2 exhibited potent antifungal activity against Sclerotinia sclerotiorum, Rhizoctonia solani, and Fusarium oxysporum, achieving inhibition rates of 72.69 ± 2.81%, 68.29 ± 1.61%, and 63.02 ± 0.45%, respectively, through the production of volatile compounds and proteinaceous metabolites. Additionally, SF1+G2 demonstrated four key plant growth-promoting traits: indole-3-acetic acid (IAA) biosynthesis, ammonia production, phosphate solubilization, and siderophore secretion. In vitro assays revealed that SF1+G2 significantly reduced disease severity in root slices of Codonopsis pilosula, Angelica sinensis, and Astragalus membranaceus by 88.89%, 80.00%, and 78.57%, respectively. Under pathogen-challenged conditions, SF1+G2 not only reduced disease incidence but also improved growth parameters of Isatis indigotica seedlings and enhanced soil nutrient availability. Specifically, SF1+G2 induced systemic resistance by enhancing superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), and peroxidase (POD) activities, while increasing soluble protein and ascorbic acid (AsA) levels, thereby reducing the O2‾ production rate and malondialdehyde (MDA) content in I. indigotica seedlings. These findings highlight SF1+G2 as an eco-friendly, multifunctional microbial agent for disease prevention and plant growth promotion, offering potential for sustainable agricultural applications.