Bioprotective potential of biosynthesized copper oxide nanoparticles and copper phosphite against Alternaria-solani-induced leaf spot in pepper plants

Alternaria solani leaf spot disease (ASLS) poses a serious threat to global crop production, including peppers, resulting in notable economic losses. Bio-nanotechnology offers promising solutions for combating plant pathogens by promoting plant defenses and inhibiting pathogen growth. This study explores the effectiveness of copper oxide nanoparticles (CNPs) and copper phosphite (MAXIFOS CU®) in controlling A. solani and boosting growth and defense responses in pepper plants. CNPs were biosynthesized using Penicillium expansum first time and thoroughly characterized through various techniques. Analysis confirmed that the nanoparticles varied in shape, predominantly oval and spherical, with an average size of approximately 40.59 nm, as shown in HR-TEM images. DLS analysis indicated a mean particle size of 74.58 nm, and Zeta potential analysis at pH 7.2 revealed a negative surface charge of − 55.25 mV, attributed to the components of the fungal extract. The study demonstrated that both CNPs and MAXIFOS CU® exhibited antifungal activity against A. solani, with CNPs effectively reducing PDI by 27.5% and enhancing overall plant protection by 65.62%. Results indicated that treated plants showed improvements in photosynthetic pigments, proline content (MAXIFOS CU® 28 g/L increase by 108.3%, while CNPs 81.30%), total phenolic compounds (CNPs 80.70% increase, while MAXIFOS CU® a 68.70%), H₂O₂ levels (MAXIFOS CU® decreased 22%, whereas CNPs 9%), MDA concentration (CNPs 39% decrease in MDA, while MAXIFOS CU® 34%), and the activities of POD (increased by 53.4, and 45.1% CNPs and MAXIFOS CU®) and PPO (CNPs and MAXIFOS CU® increased by 42.8 and 31.6%) enzymes. These findings highlight the potential of an eco-friendly, dual approach using biosynthesized CNPs and Cu-phosphite for managing A. solani and enhancing pepper plant health.