Biotic elicitors as a means of increasing isoflavone concentration of soybean seeds

Soybean (Glycine max) seeds contain isoflavones that have positive impacts on human health. Four greenhouse experiments were conducted to determine if isoflavone concentration of mature soybean seeds could be increased using elicitor compounds. The effects on soybean seed isoflavone concentrations following foliar applications of two lipo‐chitooligosaccharides (LCO) [Bj V (C_18:1 MeFuc) and Bj V (Ac, C¹⁶, MeFuc)], chitosan, actinomycetes spores (Streptomyces melanosporofaciens strain EF‐76) and yeast extract at different concentrations and growth stages were evaluated. Combined chitosan seed treatment and foliar applications were also evaluated. Concentrations of daidzein, genistein, glycitein, and total isoflavones were determined by HPLC. Foliar applications of LCOs, chitosan, and actinomycetes caused a marked increase in individual and total isoflavone concentration (ranging between 21% and 84%) of mature seeds when compared to untreated control plants. There were limited differences between the different concentrations and stages of application tested for chitosan and actinomycetes; however, response to LCOs was greatest at higher concentrations (i.e. 10^‐6 M) when applied at the early podding stage. Compared to untreated plants, combined seed treatment and foliar applications of chitosan increased individual and total isoflavone concentration of mature soybean seeds by 16% to 93%. Trends were similar for different cultivars, however, the magnitude of the response varied. Finally, response to foliar applications of yeast extract was highly concentration dependent with increases of up to 56% in total isoflavone observed with 2 mg mL^‐1. Results indicate that elicitors hold promise as a way of increasing isoflavone concentration of mature soybean seeds.