In vitro analysis of antimicrobial and phytochemical properties of crude extracts of selected plants against the tomato wilt disease

Abstract

The wilt disease by fungal and bacterial pathogens is one of the most devastating diseases of tomato (Solanum lycopersicum L.) worldwide. Chemical-based control of the wilt-causing pathogens often leads to environmental pollution and pest resistance; hence the need for alternative sustainable approaches. We evaluated the in vitro antimicrobial and phytochemical properties of aqueous crude extracts of roots, leaves, flowers, and barks of Solanum incanum L., Laurnea cornuta, Tagetes minuta L., Ageratum conyzoides, Opuntia monacantha, and Euphorbia tirucalli L. from Kano-Kisumu against Erwinia chrysanthema, Ralstonia solanacearum and Fusarium oxysporum isolated from diseased tomato tissues and rhizospheres. Sterile distilled water and the amoxicillin antibiotic were used as negative and positive control treatments, respectively. The experiment was carried out in diameters of zones of inhibition and levels of phytochemicals determined. Ageratum conyzoides and O. monacantha extracts were least effective against the pathogens, with means of inhibition of only up to 8.7 and 12.3 mm, respectively. Euphorbia tirucalli and L. cornuta were the most effective against the pathogens, with means of inhibition of up to 30 mm. Except for anthocyanins and anthraquinones, no significant (P<0.05) differences were observed for levels of other phytochemicals in different plant extracts. We concluded that plant extracts showing remarkable antimicrobial activities against the pathogens can be used to make viable formulations to combat the devastating tomato wilt disease.

Key words: Bacterial wilt, plant extracts, Solanum lycopersicum