Eco-friendly managing of root rot and wilt diseases in marjoram plants by chitosan-copper nanoparticles: enhancing plant immunity and stimulation of resistance genes.

With increased use of agrochemicals to protect crops against phytopathogenic diseases, the environment is facing serious hazardous effects. The proven antimicrobial properties of nanomaterials may provide a new level of sustainable development and rapid research for the potential to replace chemical fungicides in crop protection. The objective of this study was to investigate the in vitro and in vivo antifungal activity of chitosan-copper nanocomposite (Ch-Cu NPs) against Rhizoctonia solani and Fusarium oxysporum to control root rot and wilt disease of marjoram plants. The chemically synthesized Ch-Cu NPs nanocomposite was characterized with respect to its morphological features and size, which were obtained by Transmission Electron Microscope (TEM) analysis, and the presence of functional chemical groups responsible for the synthesis of Ch-Cu NPs was determined using Fourier Transform Infrared (FTIR) spectrophotometer. Antifungal activity against the two pathogenic fungi was assessed using three concentrations (25, 50, and 100 mg/l) of Ch-Cu NPs. The laboratory evaluation showed that mycelial radial growth of F. oxysporum and R. solani was inhibited by 80.55% for two fungi at 100 mg/L of Ch-Cu NPs. The morphology of F. oxysporum and R. solani was investigated, and molecular identification was conducted to prove that F. oxysporum and R. solani were the causal agents of root rot and wilt disease of marjoram plants in Egypt. Pathogenicity test showed that both F. oxysporum and R. solani were virulent with the measured disease incidence was 59.14% and the disease severity was 28.47%, respectively. In this work, Ch-Cu NPs at 50 mg/L were found to be the appropriate concentration that could lead to a reduction in disease incidence by 23.67% and disease severity by 5.57% with induction of plant defense. The results of HPLC analysis revealed an increase in 7 out of 9 polyphenols in 50 mg/L Ch-Cu NPs application compared to the untreated control plants. Molecular studies using qRT-PCR technique on marjoram leaf tissue were done to determine the relationship between polyphenols biosynthesis and the expression of responsible genes affected by Ch-Cu NPs application. Genes such as CAD, C4H, TAT, FLS, EGS, HPPR, PAL, and RAS showed an upregulation of their expression in marjoram treated leaves compared to the control leaves. The release profile of Ch-Cu NPs also showed an important insight into the mode of disease control. The conclusion of this work is considered as an important step toward the application of nanomaterials in agriculture, where the biosynthesized and biodegradable Cu-chitosan NPs have better biological control compatibility as it can induce similar effects to natural plant defense elicitors and antioxidant defense to prime the crop for better resistance.