Antimicrobial Activity of <i>Tithonia diversifolia</i>, <i>Elephantopus scaber</i>, and <i>Kigelia africana</i> 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.

Phytochemical analysis and antifungal activity of Tithonia diversifolia and Kigelia africana extracts against Fusarium oxysporum in tomato

“…As the concentration of K. africana extract increased, the mean mycelia diameter decreased (the inhibition zone increased). This supports similar research findings on the anti-fungal activity of K. africana against F. oxysporum (Itonga, 2011;Zofou et al, 2013;Rejeki and Addy, 2017). Kigelia africana extracts are reported to induce the disruption in fungal cell metabolism, increased permeability of fungal plasma membrane and destruction of the conidial wall structure (Al-Mujammaa'e, 2008).…”

“…As compared to T. diversifolia, extracts of K.africana did not show the presence of alkaloids and steroids. Similar studies indicate that the fruit extract of K. africana contains a high amount of flavonoid and tannin content, with very low content on alkaloid compared to other plants (Rejeki and Addy, 2017;Abdulkadir et al, 2015). The absence of alkaloids in fruits has been reported by Bondjengo et al (2017) and is attributed to differences in plant species or type of method used in extraction.…”

“…These are bioactive compounds with antimicrobial activity and they could have been attributed to the ability in inhibiting growth of F. oxysporum. Alkaloids, tannins, flavonoids and saponins display several biological properties and have been reported to have antimicrobial activity against several pathogenic microorganisms (Avato et al, 2006;Rejeki and Addy, 2017). Terpenoids and phenolics on the other hand are essential oils that inhibit microbial oxygen uptake and oxidative phosphorylation (Griffin et al, 1999).…”

“…Combined ratio (ml) (K. africana: T. diversifolia) the growth of pathogens due to their bioactive compounds (Rejeki and Addy, 2017;. They also have medicinal value and have been among many medicinal plants tested for antimicrobial activity (Neela et al, 2014).…”

“…Benth was screened for bioactive compounds and assessed for their potency in controlling plant fungal pathogen F. oxysporum that causes Fusarium wilt in tomatoes. Both plants have antimicrobial substances that have been successfully demonstrated against food and human pathogens Saini et al, 2009;Rejeki and Addy, 2017).…”