A Native Bacillus subtilis Strain from Mali Improves Peanut Yield and Offers Sustainable Control against Aflatoxin Contamination under Field Conditions

Abstract

Aflatoxin contamination of peanuts, caused by toxic metabolites produced by Aspergillus flavus, poses a major threat to public health and export opportunities in Mali. Current control strategies are either costly or poorly effective under field conditions, limiting their adoption by smallholder farmers. This study evaluated the efficacy of a native Bacillus subtilis (BS) strain, isolated from Malian soils, as a dual-action bio-inoculant for reducing aflatoxin levels while improving peanut agronomic performance under field conditions. A split-plot factorial design with four replications was implemented to compare two peanut varieties (Fleur 11 and Keniana tiga) subjected to four treatments, namely water control (NC), BS (5.6×10⁶ CFU/mL), Mancozeb fungicide (MZ), and the BS+MZ combination. Measured parameters included plant height, nodulation, root biomass, pod weight, and aflatoxin content (quantified using the RAPTOR® assay). Data were analysed using two-way ANOVA followed by Tukey’s test (α=0.05). The BS treatment alone significantly increased plant height (+60% at 25 days after sowing), nodule number (260 vs 140), and pod weight compared with the control. Most notably, BS reduced median aflatoxin contamination by nearly 80% (median 10 vs 55 ppb for the control), outperforming the fungicide MZ (median 40 ppb). The BS+MZ combination provided no additional benefit. Correlation analyses revealed a strong association between toxin reduction, early vigour, and nodulation, suggesting the induction of systemic resistance in the plant. This dual-action bio-inoculant represents an effective and sustainable biological approach, combining antifungal protection with plant growth promotion. Its adoption could reduce reliance on chemical fungicides while improving the food safety of peanut harvests in Mali. Further studies are required to optimise large-scale production and assess its long-term effects on nitrogen fixation and soil microflora.