Foliar penetration enhanced by biosurfactant rhamnolipid

• Rhamnolipid shows much better surface activity and wettability than APG.
• Rhamnolipid could resist the deposition/evaporation of glyphosate on plant leaf.
• Rhamnolipid could significantly improve the penetration across cuticular membrane.
• Rhamnolipid greatly enhances herbicidal actitivity of glyphosate.

With recent environmental and health concerns, biosurfactants have obtained increasing interest in replacing conventional surfactants for diverse applications. In agriculture, the use of surfactant in stimulating foliar uptake is mainly for wetting leaf surface, resisting deposition/evaporation, enhancing penetration across cuticular membrane (CM) and translocation. This paper aimed to address the improved foliar uptake by rhamnolipid (RL) in comparison with the currently used alkyl polyglucoside (APG). As found, compared with APG at 900 mg/L (1 × critical micellar concentration, CMC), RL at a much lower concentration of 50 mg/L (1 × CMC) showed much better wettability and surface activity, indicative of its high effectiveness as surfactants. Its performance on resistance to deposition and evaporation was at least as same as APG. Moreover, RL could significantly improve the penetration of herbicide glyphosate and other two small water-soluble molecules (phenol red and Fe2+) across CM at an equivalent efficiency as APG at 1 × CMC. Finally, the greatly enhanced herbicidal actitivity of glyphosate on greenhouse plants confirmed that RL and APG could both enhance the foliar uptake including translocation. Overall, RL should be more applicable than APG in agriculture due to its more promising properties on health/environmental friendliness.

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