ABSTRACT

The conventional method of controlling phytopathogens using chemical fungicides causes environmental hazards; there is a need for using alternatives that are effective and ecofriendly. Biosynthesized metal nanoparticles have successfully been used as antimicrobial agents against some phytopathogens. The aim of this research was to determine the effect of biosynthesized zinc oxide and magnesium oxide nanoparticles when used singly, and in combinations on fungal pathogens isolated from a diseased tomato plant.

Zinc oxide nanoparticles and magnesium oxide nanoparticles were synthesized using plant extracts and characterized via spectrophotometry. Fungi pathogens were isolated using a PDA medium. The pathogens were identified via morphological characteristics. Antimicrobial activity was tested using the agar-well diffusion method. Synergistic effect among the metal nanoparticles and Moringa oleifera plant extract were also tested. Data were analyzed using Two-Way analysis of variance and Duncan’s Multiple Test Range for significant means from GENSTAT version 12 software. A p < 0.05 was used for significant responses.

Spectrophotometric analysis showed that zinc oxide and magnesium oxide nanoparticles were synthesized at absorption peaks of 460nm and 400nm respectively. Two different Aspergellius species and a Eutorium species were identified as fungal pathogens from the PDA growth medium. Zones of inhibition of fungal growth spotted on culture plates were observed and interpreted as antimicrobial activity. The effect of zinc oxide nanoparticles on pathogens resulted in zones of inhibition, but there were no zones of inhibition observed from the effect of magnesium oxide nanoparticles. There were also no zones of inhibition observed from the synergistic effect test. The results showed that zinc oxide nanoparticles at different concentrations had significant antimicrobial activity on fungal growth. The concentration of zinc oxide nanoparticles at 100% had the highest rate of antimicrobial activity on Eurotium species which further shows that Aspergillus species were more resistant to fungicides than Eurotium species. Magnesium oxide nanoparticles do not have antimicrobial effect on Aspergillus and Eurotium species when applied singly, and can neutralize the antimicrobial effect of zinc oxide nanoparticles, making it ineffective when used in combination. The use of zinc oxide nanoparticles as a fungicide needs to be investigated by further studies.