Potential of chitosan and silver nanoparticles as fungicides against chocolate spot of faba bean: physiological, ultrastructural and toxicity studies

This study aimed at evaluating the effectiveness of chitosan nanoparticles (ChNPs), silver nanoparticles (AgNPs) and their combination (Ch-AgNPs) in controlling the chocolate spot of faba bean caused by Botrytis fabae. Five isolates of B. fabae were collected from diseased faba bean plants and screened for pathogenicity on the most susceptible faba bean cultivar, Giza 843. Among the isolates, B. fabae isolate No.3 exhibited the highest virulence. Antifungal effects of ChNPs, AgNPs (with an average particle size of 15 and 42 nm, respectively), and Ch-AgNPs mixture at 5, 10 and 20 ppm were assessed against B. fabae isolate No.3. In vitro experiments demonstrated that the Ch-AgNPs mixture at 20 ppm exhibited the greatest inhibitory effect on the mycelial growth of B. fabae, with a reduction of 100% compared to the individual nanoparticles. Transmission electron microscopy revealed notable cellular changes in B. fabae cells treated with the Ch-AgNPs mixture. Greenhouse results exhibited that the great reductions in disease severity were achieved with Tridex 80% WP® fungicide (96.51%), followed by Ch-AgNPs mixture with 84.53% reduction. The Ch-AgNPs mixture effectively enhanced the activity of peroxidase and polyphenoloxidase enzymes and the total phenol content in the plants. Application of ChNPs, AgNPs, and the Ch-AgNPs mixture significantly improved faba bean growth and yield parameters. However, the cytotoxicity assay indicated a concentration-dependent toxic effect of Ch-AgNPs, with no significant hemolytic activity observed in red blood cells. In conclusion, the Ch-AgNPs mixture was promising as a fungicide for combating the chocolate spot in faba bean.