Differences in suppression rates of crop pathogens and antioxidant activity at different harvesting times of Taraxacum mongolicum

This study was conducted to determine the suppression rates of extracts of the aerial parts of T. mongolicum collected at different harvesting times and prepared using different extract methods (water, boiled water and ethanol) on Pyricularia oryzae, Rhizoctonia solani Kühn and Colletotrichum coccodes. Additionally, the aerial parts of plants collected at different harvesting times were analyzed for phenol and flavonoid contents, DPPH scavenging activities and growth differences. Although the suppression rates of P. oryzae, Phytophthora capsici and Colletotrichum acutatum increased with increasing concentrations of water or boiled water extracts of T. mongolicum, the levels of suppression were low. In addition, the levels of suppression of the above three pathogens differed with harvesting time. P. oryzae, C. acutatum and P. capsici were 20–65, 10–60 and 5–95% suppressed by 5% ethanol extracts of T. mongolicum collected at different harvesting times, respectively. Generally, the order of suppression rates against the above three pathogens by T. mongolicum extract was July > June > May > April. Total phenol and flavonoid contents and DPPH radical scavenging activities of T. mongolicum extracts did not differ significantly among harvesting times. However, plant height and shoot dry weight of T. mongolicum sampled in July were much higher than those of plants collected in April, May and June. Thus, growth of T. mongolicum harvested at different times may be related to the higher suppression rates of ethanol extracts of T. mongolicum harvested in July.