In vitro studies of 3-O-Methylquercetin against phytopathogenic fungi of major cereals

Maize, wheat, and rice are major cereal crops in the world, which provide more caloric energy than any other type of cereal class. In recent years, the yield of these cereal grains has stagnated due to a myriad of constraints, including infestation by pests and pathogens. Plant pathogens, especially agricultural phytopathogenic fungi, may be resistant to the available chemical fungicides which may have detrimental effects and are expensive. This study investigated whether natural products isolated from Linzia glabra Steetz of family Asteraceae could be used as alternative antifungals for control of cereal diseases caused by agricultural fungi. A single pure fraction was separated and identified from L. glabra methanolic flower crude extract using high performance liquid chromatography and high resolution mass spectrometry methods. The pure fraction isolated was tested for inhibition of spore germination in vitro against Fusarium graminearum, Fusarium oxysporum, Fusarium verticillioides, Zymoseptoria tritici, Ustilago maydis, and Pyricularia oryzae. The fraction was identified as a flavonol, 3-O-Methylquercetin using high resolution mass spectrometry. Among the fungi tested, spores of Z. tritici were the most susceptible to 3-O-Methylquercetin (44% spore inhibition), followed by F. oxysporum (33% inhibition) at 27 μg/mL. Azoxystrobin, a standard commercialized fungicide, gave a complete inhibition of 100% against Z. tritici and 58% inhibition against F. oxysporum at 5 μg/mL. L. glabra contains flavonols with antifungal activity, but the modest and weak antifungal activity of 3-O-Methylquercetin compared to a standard such as azoxystrobin demonstrates the challenge to produce highly potent natural product fungicides. There is need for continued search for antifungals with new modes of action as solutions to challenges in agricultural production.