<i>Bacillus velezensis</i> and Zinc Oxide Nanoparticles in Suppressing <i>Colletotrichum capsici</i>‐Induced Anthracnose Disease in Chili: Mechanistic Insights Into Antioxidant System and Plant Growth

The effectiveness of Bacillus velezensis and zinc oxide nanoparticles (ZnONPs) as potential treatments to control fungal infection in chili peppers was investigated. We conducted greenhouse trials involving inoculation alongside in vitro tests. Plants were inoculated either with ddH₂O (control), Colletotrichum capsici (CC), Bacillus velezensis (BV), zinc oxide nanoparticles (ZnONPs), or combination BV + ZnONPs (BZC). The results indicate that BV, ZnONPs, and BZC significantly increased the activity of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and glutathione S-transferase (GST). The amount of accumulated lignin also increased, as did the activity of cinnamate 3-hydroxylase (C3H), glutathione reductase (GR), dehydroascorbate reductase (DHAR), and monodehydroascorbate reductase (MDHAR). Treatment also resulted in a reduction of malondialdehyde (MDA) content and reactive oxygen species (ROS). Moreover, BV and ZnONPs treatments resulted in longer fruit length and plant height. BV and ZnONPs treatments exerted a remarkable positive effect by increasing the chlorophyll fluorescence parameters, photosynthetic indices, and gas exchange parameters, and by upregulating the expression of defense genes compared to the CC treatment. In addition, the proline, phenol, flavonoid, and mineral contents all increased compared to the results in the CC and control groups. The confrontation assay results showed that BV and ZnONPs had notable inhibitory effects on C. capsici growth and reduced the incidence of greenhouse diseases. Ultimately, BV and ZnONPs and their combination (BZC) led to an increase in the yield of chili fruit by enhancing plant growth, number of fruits, and fruit length, indicating their potential in reducing anthracnose disease in greenhouse chili production.