Antimicrobial activity of bioactive crude extracts of Morinda royoc L. roots grown in Cuba

Abstract

The aim of this work was to determine the in vitro antimicrobial activity of the anthraquinone-rich crude extract of Morinda royoc L. roots. Its inhibitory activity was tested on two plant-pathogen bacteria (Xanthomonas campestris pv phaseoli and Pectobacterium carotovorum subsp. carotovorum), two human-pathogen bacteria (Bacillus licheniformis and Stenotrophomonas maltophilia) and three plant-pathogen fungi (Rhizoctonia solani Kϋhn, Stemphylium solani Webber and Sarocladium oryzae Sawada). The extract was prepared at 10 mg·ml^-1, previously obtained by Soxhlet extraction method. To evaluate the antimicrobial activity on bacteria, the agar diffusion method was used, whereas the microdilution method was developed to evaluate the inhibitory activity against fungi. The results obtained from this study demonstrated that the anthraquinone-rich extract was effective in inhibiting more than 50 % of Xanthomonas campestris growth without significant differences between the different doses. After 48 hours and under the same conditions, growth inhibition ca. 50 % of Bacillus licheniformis and Stenotrophomonas maltophilia was observed at the doses of 150 and 450 µg, respectively. On the other hand, all the selected fungi in this study showed susceptibility to the extract after 48 hours of incubation. The highest antifungal activity was achieved on Rhizoctonia solani, with a growth reduction ca. 50 % at concentrations of 1.25 and 2.5 mg·ml^-1. After 72 hours of incubation, no significant differences were observed in the growth of any of the three fungi. From all the pathogens selected for this study, only Pectobacterium carotovorum showed no susceptibility to any of the evaluated doses of the extract.