Phytochemical constituents and extracts of the roots of Scutellaria baicalensis exhibit in vitro and in vivo control efficacy against various phytopathogenic microorganisms

Abstract

Scutellaria baicalensis is one of the most well-known medicinal herbs used in traditional Chinese herbal medicine. During our search of antimicrobial botanicals, the methanol extract from the roots of S. baicalensis displayed in vivo control efficacy against various fungal plant diseases and in vitro inhibition against phytopathogenic bacteria. In an in vitro antifungal bioassay, ethyl acetate-soluble extract was highly active against the growth of Magnaporthe oryzae and Phytophthora sp. mycelia in the range of 500 to 5000 µg/mL. Through antifungal activity-guided bioassay, bioactive flavonoids and an oligosaccharide were identified from the EtOAc soluble extract of S. baicalensis roots by ESI-MS and 1D- and 2D-NMR data analyses. These constituents were assessed for their in vitro and in vivo antifungal activities. The major bioactive flavonoids SB1 (wogonin), SB4 (baicalein), and SB5 (baicalin) in the extracts of S. baicalensis’s roots were quantified by HPLC method. Among these three compounds, SB1 exhibited the best in vitro antifungal effect against M. oryzae and in vivo efficacy (63%) against rice blast at 500 µg/mL. SB4 was the most active against plant bacteria Acidovorax avenae subsp. cattlyae, Clavibacter michiganensis subsp. michiganensis, and Ralstonia solanacearum with an MIC value of 19 µg/mL. Moreover, the emulsion-type formulation containing the ethyl acetate-soluble extract of S. baicalensis significantly suppressed the development of rice blast caused and rice leaf blight on the rice plants in vivo. This is the first report that demonstrated bioactive constituents and extracts derived from S. baicalensis plants, which are promising to develop botanical fungicide and bactericide to control various plant diseases.