Biosynthesis of silver nanoparticles using Phoma herbarum and evaluation of their fungicidal effects against onion basal root rot disease.

This study aims to evaluate the effectiveness of a new alternative biofungicidal product in controlling the fungal disease agent, Fusarium oxysporum f. sp. cepae, which causes considerable losses during onion storage. In the first stage of this study, silver nanoparticles derived from the microorganism (Phoma herbarum) were biosynthesized using the green synthesis method in nanotechnology. Characterisation tests of the nano product, which was synthesized through the biosynthesis process, confirmed that it is a silver-based nano product with size dimensions ranging from 4 to 40 nm. In the second phase of the study, the fungicidal efficacy of the synthesized silver nanoparticle product, at concentrations ranging from 2.5 to 500 ppm, was investigated against pathogenic fungi. Its effectiveness was evaluated under both in vitro and in vivo conditions. In the in vitro study conducted in petri dishes, the highest mycelial growth, 87.66 ± 0.57 mm, was observed in the control group. Following the application of 2.5 and 5 ppm silver nanoparticles, the mycelium diameter measured 86.66 ± 1.15 mm. However, as the concentration of silver nanoparticles increased, a significant reduction in mycelial growth was observed. At 200 ppm, the mycelial diameter decreased to 10.66 ± 1.15 mm; at 500 ppm, no mycelial growth was observed. In the in vivo study conducted on onion bulbs, the fungicidal activity of silver nanoparticles was evaluated by measuring the disease inhibition rates after the application of silver nanoparticles on the bulbs. When disease inhibition rates are compared in onion bulbs, the dose-dependent rot diameters are 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). In addition to these results, different concentrations of silver nanoparticles demonstrated a dose-dependent reduction in disease incidence, ranging from 28.89% to 94.42%. When evaluated collectively, the results indicated that silver nanoparticles synthesized through the green synthesis method exhibited varying degrees of fungicidal activity under both in vitro and in vivo conditions, with effectiveness dependent on the concentration applied. Consequently, the synthesized silver nanoparticles product has demonstrated considerable potential as an alternative solution for effectively managing Fusarium oxysporum f. sp. cepae a significant threat to stored onion bulbs.