Effects of different fractions of Rheum palmatum root extract and anthraquinone compounds on fungicidal, insecticidal, and herbicidal activities

Abstract

This study was conducted to evaluate the suppression of Pyricularia oryzae, Colletotrichum coccodes, Rhizoctonia solani, Phytophthora capsici, and Botrytis cinerea, as well as the acaricidal activities against the two-spotted spider mite (Tetranychus urticae) and the weed control efficacy of solvent fractions of Pheum palmatum extract. In addition, we determined the inhibitory activities of the main bioactive substances of R. palmatum (aloe-emodin, emodin, chrysophanol, and physcion) against the aforementioned pathogens. The suppression rates of 5% ethylacetate and BuOH fractions against P. oryzae were 70 and 52%, respectively. However, the other fractions including hexane showed very little suppression of P. oryzae. Moreover, C. coccodes, B. cinerea, R. solani, and P. capsici were suppressed by 61, 47, 58, and 91% in response to treatment with the 5% ethylacetate fraction of R. palmatum, respectively, compared with the control. The ethylacetate and BuOH fractions were also confirmed in greenhouse trials of rice seedlings infected by P. oryzae. The ethylacetate and BuOH fractions of R. palmatum ethanol extract were shown to have the potential for control of powdery mildew (Sphaerotheca fuliginea causes) and weeds, but not to have acaricidal activities against the two-spotted spider mite. The suppression rates of P. oryzae and P. capsici increased with increasing concentrations of chrysophanol, emodin, aloe-emodin, and rhein, but these extracts had no effect on cucumber powdery mildew or two-spotted spider mites. The anthraquinone levels in the ethylacetate fraction were much higher than in the BuOH fraction. Thus, the higher suppression of P. oryzae and P. capsici of the ethylacetate fraction observed in this study may be related to higher levels of anthraquinone substances in the ethylacetate fraction than the BuOH fraction.