Biosynthesis of silver nanoparticles by using Phoma herbarum and control efficacy against onion basal root rot disease

Onion basal root rot disease, caused by Fusarium oxysporum f.sp. cepae (FOC), can lead to crop losses during storage. Nanotechnology is an emerging field with significant potential across various sectors, including agriculture. The aim of this study was to investigate the possibility of biosynthesising silver nanoparticles (AgNPs) using Phoma herbarum and to assess their control effects on basal rot disease in onion at different concentrations(2.5–500 ppm). The synthesised AgNPs, measuring 20 to 40 nm, were confirmed and characterised by UV–Vis spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS) and FT-IR analysis. Additionally, the study aimed to examine their effects on FOC both in vitro and in vivo at different concentrations. In vitro study, in the control group, the mycelial growth measured 87.66 ± 0.57 mm. As the concentration of AgNPs increased, there was a notable reduction in mycelial growth: at 2.5 ppm the growth was 86.66 ± 1.15 mm, at 5 ppm it remained the same at 86.66 ± 1.52 mm, at 10 ppm it decreased to 65.00 ± 2.00 mm, and further reductions were observed at 25 ppm(51.33 ± 1.52 mm), 50 ppm (47.00 ± 2.00 mm), 100 ppm(22.66 ± 2.51 mm), and 200 ppm(10.66 ± 1.15 mm). The highest concentration of 500 ppm, there was complete inhibition of mycelial growth(p ≤ 0.05). Mycelial inhibition ratios increased in a dose-dependent and ranged between 1.14 and 100%. When the disease inhibition rates of AgNp at different concentrations were compared on the onion tubers, the rot diameters depending on the dose were as follows: Positive control (50.20 ± 0.20 mm); 10 ppm (34.60 ± 0.50 mm); 25 ppm (27.60 ± 0.30 mm); 50 ppm (19.00 ± 0.38); 100 ppm (12.00 ± 0.40);200 ppm (6.80 ± 0.31 mm) and 500 ppm (1.20 ± 0.17 mm)(p ≤ 0.05). Finally, different concentrations of AgNPs, demonstrated an effective dose-dependent reduction in disease incidence, achieving reductions ranging from 28.89–94.42%. SEM analysis revealed that AgNPs caused significant disruption to the FOC mycelial structures, leading to observable plasmolysis of the hyphae. This study confirms that AgNPs can be effectively biosynthesised using P. herbarum . Furthermore, the synthesised AgNPs exhibit effective control against the onion rot disease agent when applied at various concentrations.