Plants are affected by a number of severe conditions including damages caused by phytopathogens, which ultimately reduce productivity. Overtime, plants have evolved different mechanisms for defence against and resistance to invading pathogens, such as bacteria, viruses and fungi in different pathosystems. Defence mechanisms in plants could either be innate or artificial. Innate defence is said to occur when plants are naturally able to limit the development of a specific pathogen or the damage it may cause based on properties inherent in the plant without human intervention. This defence strategy could be divided into pre-existing and induced defence mechanisms. The pre-existing defence strategy comprises defence gardgets endogenously present in the plant even before pathogen colonization. It include the use of superficial structures (such as thick walled tissues, waxes and cuticle), biochemical substances (such as inhibitors released by plant into its environment) and defence through lack of essential factors (such as lack of host receptors and sensitive sites for toxins). The induced defence mechanism only becomes active in response to pathogen attack. It consists of defence through the formation of structures (such as cytoplasmic and cellular defence structures) and through biochemical reactions or the production of certain substances (such as pathogenesis related proteins and phenolics). Proper understanding of plant defence mechanisms against pathogens is important in developing new and improved disease resistant varieties.

Among all the noble nanoparticles, silver nanoparticles have gained boundless interests because of their unique properties such as chemical stability, catalytic and most important antimicrobial activities. This study was carried out to investigate the antibacterial activity of phytosynthesized silver nanoparticles against bacteria pathogens isolated from diseased tomato plant leaves. Silver nanoparticles were synthesized using Citrus peel extract and the formation of nanoparticles was monitored using spectrophotometer. Diseased tomato plant leaves were obtained from a farm located at Ovia North-East Local Government Area, Edo State, Nigeria for the isolation of bacteria pathogens. The isolated bacteria include Pseudomonas sp. and Enterobacter sp. Antibacterial testing using the phytosynthesized silver nanoparticles was carried out via the agar well diffusion method on the test isolates. Zones of inhibition of 10 and 8 mm were obtained for Enterobacter and Pseudomonas species respectively by 100 µl nanoparticles treatment after 24 hours of incubation. This indicated that the phytosynthesized silver nanoparticles have antibacterial activity against the bacterial pathogens. Further studies should be carried out to determine the mode of action of silver nanoparticles and the potential of the test nanoparticles in plant disease management. The potential of members of the genus, Enterobacter as causative agents of plant diseases should be further investigated.

Phytopathogens have coexisted with their host plants from the beginning of their existence, relying on them for shelter and nutrients to survive, therefore leading to a constant attack of host plants. On the other hand, host plants have evolved several strategies to defend themselves against pathogen attack. The attacks and counter-attacks can be likened to an “arms race”, between two nations at war. Pathogens evolved strategies (arms) which include exertion of mechanical forces and secretion of biochemical substances such as enzymes and growth regulators, to attack susceptible host plants. These strategies are facilitated by the inability of the host plants to recognize certain molecules, known as PAMPs (Pathogen-Associated Molecular Patterns) from the pathogens. In a counter attack, host plants have developed receptors to recognize the presence of pathogens and PAMPs. This recognition activates PAMP-triggered immunity (PTI), thereby making the hitherto host plants resistant. Pathogens have further evolved another set of “arms”, known as secretion systems and effector genes, whose gene products suppress PTI, thus causing diseases. As the arms race continued, plants have evolved effector-triggered immunity (ETI) by developing intracellular resistance genes, thereby resulting to a hypersensitive reaction that follows the gene-for-gene concept. Presently, some pathogens have developed mechanisms for the suppression of ETI. In some plant-pathosystems, the plants are winning, while in others, the pathogens are winning. Phytopathological research should therefore be directed towards assisting susceptible plants to defeat phytopathogens, in order to ensure food security.

Nanoparticles are substances ranging from 1 – 100 nm in size and they have improved property such as increased surface area to volume ratio. In this study, in vitro antifungal activities of mancozeb/phytosynthesized zinc oxide nanoparticles against Eurotium sp. isolated from diseased cassava  plants (Manihot esculenta crantz) were determined. Zinc oxide (ZnO) nanoparticles was synthesized using Moringa leaf extract and characterization  of the biosynthesized nanoparticles was done using UV-Vis spectrophotometer. Different combinationsof zinc oxide nanoparticles and mancozeb were prepared corresponding to 25/75, 50/50 and 75/25 ZnO nanoparticles/mancozeb respectively. Antifungal testing using the test  nanoparticles/mancozeb combinations was carried out using thefood poisoning method. The results obtained from this study indicate that zinc oxide nanoparticles/mancozeb combinations significantly inhibited the growth of the test pathogen with varying rates of inhibition. One hundred percent (100 %) inhibition of Eurotium sp. was obtained by 25/75, 75/25 and 100 % nanoparticles treatments. Future direction to this study is to investigate how ZnO nanoparticles/mancozeb combinations could be used for crop protection against phytopathogens. The mode of action of the test nanoparticles should be further investigated.

The study was carried out to investigate the effect of soil mediated genetic change on growth rate of bacterial isolates from soils collected from different environments. Soil samples were collected from different sites: cow dung contaminated area, poultry, mechanic workshop, river, farmland and garden soils. Physiochemical analysis, bacteria isolation and enumeration were carried out on the different soil samples. Growth rate was determined by the measurement of turbidity at 600 nm using UV/VIS spectrophotometer on all isolates from two selected species (Pseudomonas and Staphylococcus) because of their even distribution in the soil samples. Plasmid curing was carried out on the selected isolates using 1 ml of 10% Sodium Dodecyl Sulphate as the curing agent and the growth rate of the plasmid-cured isolates were investigated. The results obtained indicated that the soil samples varied in their physiochemical properties. There were differences in the growth rates of bacterial isolates from the different soils for both Pseudomonas and Staphylococcus spp. a comparison between growth rate of test bacteria isolates before and after plasmid curing also suggested that curing significantly affected the growth rate of the test organisms in some soil samples. The results from this study suggested that the soil environments from which the various bacterial isolates were obtained had effect on the genetics of the bacteria isolates. The future direction to this study is to perform a molecular profiling of the various isolates to determine species specificity and also test for their virulence.