Nanoparticles and Chemical Inducers: A Sustainable Shield against Onion White Rot

Abstract

This study investigated the effectiveness of nanoparticles and chemical inducers in managing onion white rot caused by <i>Sclerotium cepivorum</i>. The pathogen severely threatens onion cultivation, resulting in significant yield losses and economic setbacks. Traditional fungicides, though effective, raise environmental concerns, prompting a shift toward eco-friendly alternatives. In this study, four <i>S. cepivorum</i> isolates were utilized, each exhibiting varying degrees of pathogenicity, with the third isolate from Abu-Hamad demonstrating the highest potency. During the in vitro studies, three nanoparticles (NPs) were investigated, including Fe₃O₄ NPs, Cu NPs, and ZnO NPs, which demonstrated the potential to inhibit mycelial growth, with salicylic acid and Fe₃O₄ NPs exhibiting synergistic effects. In vivo, these nanoparticles reduced the disease incidence and severity, with Fe₃O₄ NPs at 1000-1400 ppm resulting in 65.0-80.0% incidence and 80.0-90.0% severity. ZnO NPs had the most positive impact on the chlorophyll content, while Cu NPs had minimal effects. At 1000 ppm, Fe₃O₄ NPs had variable effects on the phenolic compounds (total: 6.28, free: 4.81, related: 2.59), while ZnO NPs caused minor fluctuations (total: 3.60, free: 1.82, related: 1.73). For the chemical inducers, salicylic acid reduced the disease (10.0% incidence, 25.0% to 10.0% severity) and promoted growth, and it elevated the chlorophyll values and enhanced the phenolic compounds in infected onions. Potassium phosphate dibasic (PDP) had mixed effects, and ascorbic acid showed limited efficacy toward disease reduction. However, PDP at 1400 ppm and ascorbic acid at 1000 ppm elevated the chlorophyll values and enhanced the phenolic compounds. Furthermore, this study extended to traditional fungicides, highlighting their inhibitory effects on <i>S. cepivorum</i>. This research provides a comprehensive comparative analysis of these approaches, emphasizing their potential in eco-friendly onion white rot management.