Combining multiple Bacillus spp. with fish protein hydrolysates mitigates root rot (Fusarium solani) and improves cucumber seedlings growth and substrate nutrients.

AIMS: The effect of Bacillus strains combined with fish protein hydrolysates (FPHs) on cucumber root rot disease, seedlings growth and substrate nutrients was investigated. METHODS AND RESULTS: We isolated three strains capable of mitigating cucumber root rot disease, XY-1 and XY-13 strains were identified as B. amyloliquefaciens, and XY-53 strain as B. subtilis. In the absence of bacteria, The 200×dilution (5 ml L-1 ) of FPHs was the optimum concentration for improving cucumber seedlings growth. In vivo antibiosis tests showed that combined bacteria alongside FPHs inhibited the pathogen growth by 85%~90%, higher than individual bacteria. The FPHs combined either with XY-1 and XY-53 strains or with XY-13 and XY-53 strains promoted seedlings growth under infection, whereas FPHs combined with a mixture of XY-1, XY-13 and XY-53 strains showed the highest total phosphorus and organic matter content in substrate. Moreover, FPHs combined with XY-53 strain increased urease activity, while combined either with XY-13 and XY-53 strains or with XY-1, XY-13 and XY-53 strains increased sucrase activity under infection. CONCLUSIONS: FPHs combined with B. amyloliquefaciens and B. subtilis had great potential to suppress growth of root rot and promote cucumber seedlings and increase substrate nutrient content. SIGNIFICANCE AND IMPACT OF THE STUDY: Co-inoculation of B. amyloliquefaciens and B. subtilis with addition of FPHs is a good strategy for maintaining healthy crops.