Co-culture of Bacillus subtilis and B. amyloliquefaciens for control of maize sheath blight and growth promotion via microbial vetch fertiliser

Maize sheath blight caused by Rhizoctonia solani is a destructive disease threatening global maize production. Chemical control leads to environmental pollution and residues, so eco-friendly biocontrol strategies are urgently needed. However, single Bacillus strains often show unstable efficacy, and the synergistic system combining Bacillus co-culture with vetch fertiliser remains poorly studied. We hypothesized that co-culture of biocontrol bacteria could enhance disease control and plant growth via direct antagonism and host defense induction. Two antagonistic strains, 24-2 (Bacillus subtilis) and 26-2 (B. amyloliquefaciens), were screened and identified. In dual culture, the percent inhibition of radial growth (PIRG) reached 79.05% and 79.63%, respectively. Co-culture at a 2:8 ratio produced fermentation broth with 64.44% inhibition, significantly higher than single strains (p < 0.05). Pot experiments showed that microbial vetch fertiliser (MVF, decomposed vetch straw: co-culture broth = 6:1) significantly promoted maize growth. Compared with the control, plant height increased by 14.84%, stem diameter by 23.47%, and chlorophyll SPAD by 11.25% (p < 0.05). SOD and POD activities were 1.71-and 2.17-fold higher (p < 0.05), indicating activated plant defense. This study provides a novel synergistic biocontrol system for maize sheath blight, supporting sustainable agricultural disease management.