Growth Regulator Activity of Macro-Sorb® Foliar in Vitro

In vitro growth responses elicited by separated fractions of Macro-Sorb Foliar© (FOLIAR), a common biostimulant applied to golf course turfgrasses, were investigated using two bioassays specific and sensitive to auxin or cytokinin. Auxin responses were tested using the Avena (oat) first internode straight growth bioassay using increasing concentrations of indole-3-acetic acid as an internal standard. Cytokinin responses were tested using the Raphanus (radish) cotyledon expansion bioassay, with varying concentrations of zeatin (trans) used as a standard. Inorganic nitrogen controls were utilized in all bioassay trials to ensure that plant responses were not due to mineral nutrition. FOLIAR did not elicit a plant response similar to cytokinin, but elicited auxin-like responses in all trials which were significantly different from the control. Moreover, the lipophilic fraction elicited a significantly greater response than both the water-soluble fraction and nitrogen control. The results indicate that FOLIAR likely contains a biologically active compound which is hydrophobic in nature.