Bio-synthesised silver nanoparticles are effective in controlling several micro-organisms. They are correspondingly environmentally friendly, affordable, and easy to synthesise when compared with chemically synthesised silver nanoparticles. This study investigated the efficacy of biosynthesized silver nanoparticles against the fungus Sporisorium scitamineum, the causal agent of sugarcane smut. The reduction of silver nitrate upon mixing with the plants' crude extracts was evidenced by the change in colour of the mixture to dark brown. Optimization of the mixtures using ultraviolet-visual spectroscopy showed peaks in the range of 340 to 450 nm. The Fourier transform infrared spectroscopy analysis identified proteins to be essential capping agents, and reducing sugars were responsible for the reduction of silver nitrate to nanoparticles and stabilizing the nanoparticles. The transmission electron microscope analysis showed the sizes of the nanoparticles to vary between 3 and 70 nm. Carissa spinarum and Melia azedarach had the most antifungal activity against S. scitamineum as observed from the inhibition-zone assay. Silver nanoparticles were successfully synthesized using the selected botanicals. All the synthesized nanoparticles showed varying antifungal effects against the S. scitamineum. C. spinarum and M. azedarach exhibited the highest antifungal activity, while Azadirachta indica showed the least.
Sugarcane smut is a disease of economic importance in the sugarcane industry, occasioning losses of up to 50%. Current management practices have been ineffective in controlling the fungal disease, and hence the understanding of the pathogen and the development of appropriate control measures are required. This study investigates the morphology, virulence and molecular variability of Sporisorium scitamineum isolates from Eswatini to understand its pathogenicity for effective control. Fungal isolates were collected along the Sugarbelt in the Lowveld of Eswatini. The isolates were verified by polymerase chain reaction using the bE4 and bE8 specific primers with amplification of a 459bp fragment. The identity was further verified by DNA sequencing. The teliospores from the isolates were uniform in brown colour, spiny texture and circular shape. The teliospore sizes were significantly (P=0.05) different among the isolates. The isolate from Big-Bend had a mean spore diameter of 5.55µm, while Simunye, Nsoko and Mhlume had average diameters of 4.69µm, 4.98µm and 4.87µm, respectively. The documentation of the developmental stages revealed that the samples were of variable virulence with significantly (P=0.05) different rates of promycelium development. The variable virulence of the isolates was further confirmed by the in-vivo pathogen biomass quantification by RT-qPCR. Genetic distance matrix analysis and cluster analysis showed high homology (99-100%) among the local isolates which indicate that there is a low variability among the strains that are found in the selected sugarcane growing areas of Eswatini
Background: Sugarcane smut is a disease that is caused by the fungus Sporisorium scitamineum. This is a disease of economic importance in the sugarcane industry, because it can cause losses of up to 50%. Current management practices have shown to be ineffective in controlling the fungal disease and hence there is the need for the development of antifungal agents that are biocompatible, non-toxic, environmentally friendly and easy to develop. Biosynthesized silver nanoparticles have been found to possess antimicrobial properties, and have not been explored on S. scitamineum. Results: The synthesis of silver nanoparticles using Carissa spinarum yielded particles that were spherical, smooth and they had a size range from 3nm to 33nm in size. Optimization of the mixtures using ultraviolet-visual spectroscopy (UV-Vis) showed peaks in the range of 340nm to 450nm. The Fourier transform infrared spectroscopy analysis identified proteins to be essential capping agents and reducing sugars were responsible for the reduction of the silver nitrate to nanoparticles and stabilizing the nanoparticles. The biosynthesized silver nanoparticles had the highest antifungal activity at 5mg/ml, while the minimum inhibitory concentration and minimum fungal concentration were 78µg/ml. The in-vivo assays showed a significant (at P=0.05) reduction of the pathogen biomass concentration on the plants that were treated with the nanoparticles when compared to the control plants. The application of 58.5µg/ml of the b-AgNPs to the S. scitamineum resulted to a significant (P=0.05) increase in expression of the bE and bW genes, while the treatment with 39 µg/ml significantly (P=0.05) increased the expression of the bE gene, but had no significant (P=0.05) change in the expression of the bW gene. Conclusion: Silver nanoparticles that were synthesized successfully using C. spinarum crude extract inhibited the growth of S. scitamineum both in-vitro and in-vivo. The silver nanoparticles had a regulatory effect on the expression of the bE and bW genes in the fungus.
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