Antimicrobial Activity of Tithonia diversifolia, Elephantopus scaber, and Kigelia africana Against Plant Pathogens

Abstract

Synthetic pesticides, one among agricultural inputs, have been used and applied to crop production, particularly during plant pathogen attacks. Although promisingly, possible effect that the application of pesticides on agro-ecosystem may have to be concerned to support health of food, consumers and to the environment. Alternatively, exploration of the potential plants that probably have natural antimicrobial compounds is important step to discover natural pesticide as component of plant disease management. Some of plants with low economical value such as Tithonia diversifolia, Elephantopus scaber, and Kigelia africana have been known to have antimicrobial substances and successfully demonstrated against food and human pathogens. These, bring us to study their potency in controlling several plant pathogens of important crops, either fungal such as Phytophthora nicotianae and Rhizoctonia solani, or bacterial pathogens such as Ralstonia solanacearum and Xanthomonas oryzae. Leave extracts of both, T. diversifolia and E. scaber, and fruit extract of K. africana were obtained and concentrated using methanol. Our results showed that all extracts contained flavonoid, tannin, and alkaloid but the amount of the content of each extract was different. Among extracts used in this study, fruit extract of K. africana was known to contain the highest flavonoid and tannin content of 21, 54 µg QE/ml and 28.95 µg GAE/ml, respectively, with low content on alkaloid (3.32 µg AE/ml) compared to other plant extracts. To test it potency as biopesticides, antimicrobial activity against fungal pathogens were evaluated using poisoned food technique method while antimicrobial activity against pathogenic bacteria were evaluated using spot test method. The result showed that extract from K. africana fruit was able to inhibit fungal pathogen R. solani, while extracts of E. scaber and T. diversifolia were have inhibition ability against P. nicotianae. In addition, the E. scaber extract was also able to inhibit bacteria R. solanacearum and X. oryzae. In average, 5 mg/ml of extracts were demonstrated to give the best performance in inhibit plant pathogens.