ABSTRACT
Plants play a vital role in human life and the cultivation of these plants is faced with various threats, including pathogenic diseases. Fusarium wilt is one of the most destructive fungal diseases of plants globally and accounts for approximately 80% of the yield reduction. Control measures such as cultural, biological, physical, and chemical methods being used have their limitations. Hence, there is a need to explore other alternatives. Nanotechnology, a field of science concerned with the manipulation of nanoparticles (NPs), has found widespread application in medicine, electronics, and the food industry, but the potential in agriculture has yet to be fully exploited. The aim of this study was to investigate the potentials of controlling Fusarium wilt disease using phytosynthesized magnesium oxide nanoparticles. The syntheses of Magnesium oxide (MgO) nanoparticles was carried out under varying conditions of different plant extract sources, time of reaction, molar concentrations of precursor solution, volume ratio of plant extract to precursor solution, pH and light sources. Spectrophotometric technique was used to characterize the synthesized magnesium oxide nanoparticles. Phytopathogens were isolated from diseased tomato plants (Solanum lycopersicum. L) using conventional plating and pour plate methods. The fungal and bacterial isolates were characterized using cultural morphology, and biochemical methods. Furthermore, molecular characterization of the fungal and bacterial isolates was carried out using polymerase chain reaction (PCR) technique with primer pairs designed for internal transcribed spacer (ITS) regions and 16S rRNA sequences, respectively. Poisoned food and agar well diffusion techniques were used to investigate the antimicrobial activity of MgO nanoparticles in vitro. The in vivo study of the antifungal activity of MgO nanoparticles was carried out using the root dipping technique for tomato plants inoculation and applications of MgO nanoparticles through aerial and soil drench methods. Data was collected on plant height, chlorophyll content, percentage disease incidence and symptom score. Evaluation of the i-resistant gene expression in tomato plants against Fusarium wilt disease was done using quantitative real-time PCR. This experiment was laid out in a completely randomized design with three replicates for each treatment and the suitable controls. The data was xx statistically analyzed using descriptive and parametric statistics, with post hoc analysis using the Duncan's multiple range test, and Least significant difference set at P ˂ 0.05. The results revealed that optimal yield of MgO nanoparticles was achieved using the leaf extracts of Moringa oleifera and Vernonia amygdalina with magnesium oxide precursor solution within 48 hours of incubation, alkaline pH of 9 and 11, 0.1 and 0.01 molar concentrations of precursor salt solutions, volume ratio of plant extracts two (2) to precursor salt solution three (3) and the visible light source and dark room environments. Phytopathogens such as Fusarium oxysporum f sp lycopersici (Fol), Fusarium oxysporum f sp ciceris (Foc), Diaporthe species, Phytophthora infestans, Bacillus cereus and Pseudomonas species were isolated from the diseased tomato plants. In this study, 100% concentrations (stock) of MgO nanoparticles phytosynthesized using M. oleifera and V. amygdalina extracts significantly (P ˂ 0.05) inhibited mycelia growth of Fol with maximum inhibition of 5.50 ± 0.58 mm and 8.00 ± 2.31 mm respectively, compared to the controls with mycelia growth of 31.8 ± 0.83 mm on the fifth day of incubation. The in vivo study indicated that MgO nanoparticles were effective in controlling Fusarium wilt disease in the infected tomato plants. The percentage disease incidence was 10% in MgO nanoparticles treated tomato plants compared to 100% in the untreated control after 30 days of post inoculation (DPI). Chlorophyll content was higher (4.63 mg/L) in the tomato plants rhizoinjected with MgO nanoparticles compared to the control (0.67 mg/L) after 30 DPI. The I gene expression levels of the tomato plants treated with MgO nanoparticles were relatively the same compared to the actin gene, which serves as the reference gene. The findings of this study showed that, under specific conditions, the yield of MgO nanoparticles can be maximized. Phytosynthesized MgO nanoparticles showed remarkable antimicrobial activity in vitro against fungal and bacterial phytopathogens at the level of 100% concentrations. The research has demonstrated that the Fusarium wilt disease of tomato plants can be controlled using MgO nanoparticles.
