Antimicrobial effects of Nigerian plants against tomato (<i>solanum lycopersicum</i> l.) fruit pathogens

Abstract

Background: Sour rot and bacterial spot diseases of tomato fruit caused by the fungus Geotrichum candidum and the bacterium Xanthomonas campestris pv vesicatoria respectively, are very critical diseases around the world.
Objective : The aim of the study was to find substitutes to chemical bactericides and fungicides used to control postharvest tomato fruit diseases.
Methods : Aqueous, ethanol, methanol, chloroform, and nhexane extracts of Fifteen medicinal plants collected from Agbor, Delta State Nigeria were screened for activity against X. vesicatoria and G. candidum. The antimicrobial activities of the plants were evaluated with the paper disc diffusion assay and the food poison method.
Results : The methanol extracts of Ficus exasperata, Icacina trichantha, Jatropha curcas, Vernonia amygdalina, Aspilia africana, Chromolaena odorata outperformed the reference antibiotics in inhibiting growth of X. vesicatoria. The fungicide propiconazole outperformed all plant extracts with a mycelia inhibition growth (MIG) rate of 91.08% against G. candidum which was not significantly different from the MIG rate of methanol extracts F. exasperata (81.73%). The methanol and ethanol extracts showed stronger antibacterial and antifungal activity than other extracts because of differences in polarity. The antimicrobial activity of the plant extracts can be attributed to the bioactive secondary metabolites in them. The difference in the degree of inhibition exhibited by extracts of the same plant shows that polarity of solvents and reactivity of compounds eluted determines the final efficiency of the extract against the plant pathogens.
Conclusion : The methanol extract of Ficus exasperata can effectively protect tomato fruit from sour rot and bacterial spot diseases. The study demonstrates that medicinal plants extracts are potential sources of
biopesticides and could be used to prevent postharvest loss of tomato fruits.