Comparative efficacy of seed biopriming and soil drenching with <scp> <i>Bacillus altitudinis</i> TM22 </scp> and <scp> <i>Bacillus atrophaeus</i> MCM61 </scp> on the suppression of Fusarium wilt of cotton

BACKGROUND: Bacillus species suppress fungal pathogens by producing antimicrobial peptides. However, there is limited evidence of comparative effects of seed biopriming and soil drenching with Bacillus on pathogen suppression. RESULTS: Among six Bacillus species, B. altitudinis TM22 exhibited the highest in vitro inhibition of Fusarium oxysporum f. sp. vasinfectum (FOV) associated with Fusarium wilt of cotton. Lipopeptides (LPs) and polyketides (PKs) were extracted from the two most inhibitory strains: B. altitudinis TM22 and B. atrophaeus MCM61, where LPs from TM22 showed higher in vitro inhibition of FOV. Liquid chromatography-time-of-flight mass spectrometry (LC-TOF/MS) analysis detected iturin, fengycin, surfactin, bacillibactin, bacillomycin, bacilysin and bacillaene in TM22, whereas iturin was deficient in MCM61. TM22 produced larger amounts of hydrogen cyanide, correlating with its higher antagonistic potential. In a glasshouse experiment, TM22 and MCM61 applied via seed biopriming showed the lowest disease incidence and severity and improved plant biomass compared to soil drenching. Co-application of TM22 and MCM61 improved chlorophyll a, b, carotenoids, photosynthesis rate, RWC, and stomatal conductance. Additionally, malondialdehyde, electrolyte leakage and hydrogen peroxide levels were lower in plants treated with TM22 + MCM61 + FOV. Moreover, the activity of polyphenol oxidase (PPO), peroxidase (POD), ascorbate peroxidase (APX), catalase (CAT), superoxide dismutase (SOD), β-1,3-glucanase (GLU), phenylalanine ammonia-lyase (PAL) and chitinase (CHI) enzymes was the highest in TM22 + MCM61 + FOV-treated plants. The expression of HMGR, MPK3, GST, PAL, SOD, PPO, APX, POD and CAT genes was the highest in plants subjected to co-application of TM22 and MCM61 against FOV. CONCLUSION: Our study highlights the potential of Bacillus strains TM22 and MCM61 applied via seed biopriming and soil drenching in suppressing Fusarium wilt and enhancing biomass of cotton plants. © 2025 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.