PHYTOCHEMICAL COMPOSITION, ANTIBACTERIAL AND ALLELOPATHIC ACTIVITIES OF Achyranthes aspera AND Tagetes minuta LEAF EXTRACTS

Abstract

Antibiotic resistance remains a significant global health concern to date, putting at risk treatment options. As a result, treatments can be expensive and ineffective. It is therefore necessary to look for new options like using plant extracts with antimicrobial properties. Achyranthes aspera and Tagetes minuta have been traditionally used to treat various diseases in many communities and may possess antibacterial and allelopathic properties. Weeds cause more crop losses than insects, pests and diseases combined however their antimicrobial and allelopathic properties have not received much attention. This research aimed to determine the phytochemical composition, antibacterial and allelopathic activities of Achyranthes aspera and Tagetes minuta. Leaves were identified from the farm fields of University of Eldoret, collected, placed in sample collection bags, then transported to the laboratory. The leaves were washed, shade dried then ground to semi-powdery form. Extraction was conducted using sterile distilled water and ethanol. Extracts were tested against Escherichia coli ATCC 25922, Enterococcus faecalis ATCC 51299, Klebsiella pneumoniae ATCC 700603, Pseudomonas aeruginosa ATCC 27853 and Staphylococcus aureus ATCC 29213 by disc diffusion method in a Completely Randomized design with three replications. Ciprofloxacin was used as a positive control. Clear zones around the discs were recorded as inhibition zones in millimetres. Maize, millet, rice and sorghum seeds were dressed with extracts to establish their allelopathic activities by placing five surface sterilized seeds in each petri dish. Fifteen millilitres of extracts were used with distilled water set as a positive control. The design of the experiments was Completely Randomized with three replications. ANOVA was used to determine statistical significance at P ≤ 0.05. A. aspera and T. minuta extracts showed significant inhibitory effects with inhibition zones of ≥13 mm compared to ≥17 mm from ciprofloxacin. Bio-activity of extracts was highest on S. aureus followed by E. faecalis then P. aeruginosa then E. coli with least effect on K. pneumoniae. Plumule and radicle lengths of the test plants were also significantly affected with percentage reductions of ≥63%. Extracts were more detrimental on Rice followed by Maize then Sorghum with minimal effect on Millet. Millet recorded the highest germination percentage of 89.44% while rice had the lowest percentage at 67.78%, with Maize (87.50%) and sorghum (85.83%). Alkaloids, coumarins, flavonoids, phenols, quinones, saponins, tannins and terpenoids were present in extracts of both plants while Anthraquinones, glycosides and steroids existed only in A. aspera. This study concludes that A. aspera and T. minuta have remarkable antibacterial and allelopathic activities. There is therefore need to balance between controlling these plants which grow as weeds and maintaining them aimed at utilization for the development of newer antimicrobials and/or bio-control agents.