Rhamnolipids as Agricultural Biostimulants: Effects on Wheat Growth, Yield, and Molecular Mechanisms

With the increasing demand for sustainable agriculture, rhamnolipids (RHAs), a class of biosurfactants, have emerged as promising eco-friendly biostimulants. However, their full potential has been limited by impurities and uncertain mechanisms. This study investigated the effects of high-purity RHAs on wheat (Triticum aestivum) growth and yield through controlled laboratory experiments and multiyear field trials. In laboratory assays, optimal RHA concentrations (5-10 mg·L^-1) promoted seedling growth by enhancing chlorophyll content, root-shoot development, and tillering. Transcriptomic profiling revealed that RHA treatment upregulated genes involved in gibberellic acid (GA₃) and zeatin (ZT) biosynthesis, nitrogen uptake, and photosynthesis. In the field, low doses of RHA application (∼45 g·ha^-1) significantly enhanced tillering capacity and promoted earlier flowering while delaying senescence. Importantly, these physiological enhancements translated into significant yield increases of 11.9 and 14.8% across 2 consecutive years. The study provides novel mechanistic insights into RHA-mediated growth promotion, highlighting RHAs as a promising, eco-friendly biostimulant for sustainable wheat production.