Novel herbicide from an optimized Bacillus altitudinis D30202 solvent extract

The herbicidal activity of the fermentation broth, filtrate, and extracts of Bacillus altitudinis D30202 was evaluated against seed germination and seedling growth of wild oat (Avena fatua L.). The bacterial culture filtrate exhibited greater inhibition of the wild oat weed than the fermentation broth. The filtrate was also extracted with organic solvents. The herbicidal potency of the extracts on the growth of wild oat plants was as follows: chloroform (100% inhibition of germination) > n-butanol (93.8%) > ethyl acetate (66.7%) > petroleum ether (6.3%) > aqueous phase (2.1%); so the chloroform extract was evaluated further. It inhibited wild oat radicle growth by 100%, and plumule growth by 97.9%, while spraying young plants with a 5 mg/mL extract caused severe desiccation of the leaves, stalk wilting, and plant death. IC₅₀ values for inhibition of plumule and radicle growth and germination were 0.64–0.72 mg/mL. Scanning electron microscopy and transmission electron microscopy revealed changes in the microstructure of the leaves and root tips, and degradation of organelles following chloroform extract treatment. The 5 mg/mL extract had no adverse impact on the growth or health of highland barley (Hordeum vulgare L.), corn (Zea mays), and broad bean (Vicia faba L.), indicating that this novel bioherbicide is suitable for control of wild oat weeds in the production of these food crops (while having a minor impact on the health of pea plants and being phytotoxic to wheat plants).