ABSTRACT

Nanoparticles are small-sized materials between 1-100 nanometers. They are the basis of nanotechnology and are of different examples, which include zinc oxide nanoparticles (ZnONPs), gold nanoparticles (AuNPs), and silver nanoparticles (AgNPs) amongst others. Nanoparticles have found widespread application in agriculture, medicine, and industry. This research was aimed at determining the antibacterial activity of the different sizes of ZnO nanoparticles against diseased tomato stem pathogens. Bacteria were isolated from diseased tomato stems and these isolates were identified using morphological and biochemical tests. Zinc oxide nanoparticles were synthesized using Moringa leaf extracts and zinc nitrate hexahydrate as precursor solution. This procedure of green synthesis was carried out for 3  consecutive days to obtain nanoparticles with different incubation periods; 24 48, and 72 hours. The nanoparticles were subjected to spectrophotometric readings to get the absorbance at wavelength 250 nm -700 nm from which the sizes were determined. The nanoparticles were also used to carry out antimicrobial sensitivity tests against the suspected pathogenic bacteria. The suspected pathogenic bacterial were  Xanthomonas campestris; Pseudomonas syringae Clavibacter michiganesis. The study revealed that the highest incubation period, which was 72 hours gave the smallest nanoparticle size of 5nm and had the highest antibacterial activity against Clavibacter michiganesis. The nanoparticle of 48 hours incubation gave a nanoparticle size of 26 nm while that of the 24 hours gave a nanoparticle size of 7 nm.The findings of the study revealed that 5 nm ZnO nanoparticles which had the highest antibacterial activity may be investigated as a means of reducing pathogen attacks on tomato plants being cultivated.