The application of microbial products as natural biocontrol agents for inducing systemic resistance against plant viral infections represents a promising strategy for sustainable and eco-friendly agricultural applications. Under greenhouse conditions, the efficacy of the culture filtrate of Bacillus subtilis strain HA1 (Acc# OM286889) for protecting tomato plants from Tobacco mosaic virus (TMV) infection was assessed. The results showed that the dual foliar application of this culture filtrate (HA1-CF) 24 h before and 24 h after TMV inoculation was the most effective treatment for enhancing tomato plant development, with substantial improvements in shoot and root parameters. Furthermore, compared to non-treated plants, HA1-CF-treated tomato had a significant increase in total phenolic and flavonoid contents of up to 27% and 50%, respectively. In addition, a considerable increase in the activities of reactive oxygen species scavenging enzymes (PPO, SOD, and POX) and a significant decrease in non-enzymatic oxidative stress markers (H₂O₂ and MDA) were reported. In comparison to untreated control plants, all HA1-CF-treated plants showed a significant reduction in TMV accumulation in systemically infected tomato leaves, up to a 91% reduction at 15 dpi. The qRT-PCR results confirmed that HA1-CF stimulated the transcription of several defense-related tomato genes (PR-1, PAL, CHS, and HQT), pointing to their potential role in induced resistance against TMV. GC–MS analysis showed that phenol, 2,4-bis (1,1-dimethylethyl)-, Pyrrolo [1,2-a] pyrazine-1,4-dione, hexahydro-3-(2-methylpropyl)- and eicosane are the primary ingredient compounds in the HA1-CF ethyl acetate extract, suggesting that these molecules take part in stimulating induced systemic resistance in tomato plants. Our results imply that HA1-CF is a potential resistance inducer to control plant viral infections, a plant growth promoter, and a source of bioactive compounds for sustainable disease management.

Tobacco mosaic virus (TMV) is a major pathogen affecting tomato plants worldwide. The efficacy of silver nanoparticles (Ag-NPs) mediated by Punica granatum biowaste peel extract in mitigating the negative impact of TMV infection on tomato growth and oxidative stress was investigated through scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV-Visible (UV-Vis) spectrophotometer, X-ray Diffraction (XRD), dynamic light scattering (DLS), zeta potential, energy-dispersive X-ray spectroscopy (EDX), and Fourier-transform infrared spectra (FTIR). Results of SEM analysis of green Ag-NPs revealed the presence of condensed spherical or round NPs with diameters ranging between 61 and 97 nm. TEM confirmed the SEM results and showed round-shaped Ag-NPs with an average size of 33.37 ± 12.7 nm. The elemental analysis (EDX) of prepared Ag-NPs revealed the presence of elemental Ag as a major peak (64.43%) at 3–3.5 KeV. The FTIR revealed several functional groups on the prepared Ag-NPs, for which three treatment strategies for Ag-NP applications were evaluated in the greenhouse study and compared to inoculated TMV and control plants: pre-infection treatment (TB), post-infection treatment (TA), and dual treatment (TD). The results showed that the TD strategy is the most effective in improving tomato growth and reducing viral replication, whereas all Ag-NP treatments (TB, TA, and TD) were found to significantly increase expression of the pathogenesis-related (PR) genes PR-1 and PR-2, as well as polyphenolic compounds, HQT, and C4H genes compared to control plants. In contrast, the flavonoid content of tomato plants was not affected by the viral infection, while the phenolic content was significantly reduced in the TMV group. Furthermore, TMV infection led to a significant increase in oxidative stress markers MDA and H₂O₂, as well as a reduction in the enzymatic activity of the antioxidants PPO, SOD, and POX. Our results clearly showed that the application of Ag-NPs on TMV-infected plants reduces virus accumulation, delays viral replication in all treatments, and greatly enhances the expression of the CHS gene involved in flavonoid biosynthesis. Overall, these findings suggest that treatment with Ag-NPs may be an effective strategy to mitigate the negative impact of TMV infection on tomato plants.

Cucumber mosaic virus (CMV) causes a significant threat to crop output sustainability and human nutrition worldwide, since it is one of the most prevalent plant viruses infecting most kinds of plants. Nowadays, different types of nanomaterials are applied as a control agent against different phytopathogens. However, their effects against viral infections are still limited. In the current study, the antiviral activities of the biosynthesized silver nanoparticles (Ag-NPs) mediated by aqueous extract of Ocimum basilicum against cucumber mosaic virus in squash (Cucurbita pepo L.) were investigated. The prepared Ag-NPs were characterized using scanning electron microscopy (SEM), dynamic light scattering (DLS), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), Fourier transform infrared spectroscopy (FTIR) and zeta potential distribution techniques. DLS, SEM, and TEM analyses showed that the Ag-NPs were spherical, with sizes ranging from 26.3 to 83 nm with an average particle size of about 32.6 nm. FTIR identified different functional groups responsible for the capping and stability of Ag-NPs. The zeta potential was reported as being −11.1 mV. Under greenhouse conditions, foliar sprays of Ag-NPs (100 µg/mL) promoted growth, delayed disease symptom development, and significantly reduced CMV accumulation levels of treated plants compared to non-treated plants. Treatment with Ag-NPs 24 h before or after CMV infection reduced CMV accumulation levels by 92% and 86%, respectively. There was also a significant increase in total soluble carbohydrates, free radical scavenging activity, antioxidant enzymes (PPO, SOD, and POX), as well as total phenolic and flavonoid content. Furthermore, systemic resistance was induced by significantly increasing the expression levels of pathogenesis-related genes (PR-1 and PR-5) and polyphenolic pathway genes (HCT and CHI). These findings suggest that Ag-NPs produced by O. basilicum could be used as an elicitor agent and as a control agent in the induction and management of plant viral infections.

The use of microbial products as natural biocontrol agents to increase a plant’s systemic resistance to viral infections is a promising way to make agriculture more sustainable and less harmful to the environment. The rhizobacterium Paenibacillus polymyxa has been shown to have strong biocontrol action against plant diseases, but its antiviral activity has been little investigated. Here, the efficiency of the culture filtrate of the P. polymyxa strain SZYM (Acc# ON149452) to protect squash (Cucurbita pepo L.) plants against a Zucchini yellow mosaic virus (ZYMV, Acc# ON159933) infection was evaluated. Under greenhouse conditions, the foliar application of the culture filtrate of SZYM either in protective or curative treatment conditions enhanced squash growth, reduced disease severity, and decreased ZYMV accumulation levels in the treated plants when compared to the non-treated plants. The protective treatment group exhibited the highest inhibitory effect (80%), with significant increases in their total soluble carbohydrates, total soluble protein content, ascorbic acid content, and free radical scavenging activity. Furthermore, a considerable increase in the activities of reactive oxygen species scavenging enzymes (superoxide dismutase, polyphenol oxidase, and peroxidase) were also found. In addition, the induction of systemic resistance with a significant elevation in the transcriptional levels of polyphenolic pathway genes (CHS, PAL, and C3H) and pathogenesis-related genes (PR-1 and PR-3) was observed. Out of the 14 detected compounds in the GC–MS analysis, propanoic acid, benzenedicarboxylic acid, tetradecanoic acid, and their derivatives, as well as pyrrolo [1,2-a] pyrazine-1,4-dione, hexahydro-3-(2-methylpropyl) were the primary ingredient compounds in the ethyl acetate extract of the SZYM-culture filtrate. Such compounds may act as elicitor molecules that induce systemic resistance against viral infection. Consequently, P. polymyxa can be considered a powerful plant growth-promoting bacterium (PGPB) in agricultural applications as well as a source of bioactive compounds for sustainable disease management. As far as we know, this is the first time that P. polymyxa has been shown to fight viruses in plants.

Zinc oxide nanoparticles (ZnO-NPs) have gained significant attention in nanotechnology due to their unique properties and potential applications in various fields, including insecticidal and antibacterial activities. The ZnO-NPs were biosynthesized by Eriobotrya japonica leaf extract and characterized by various techniques such as UV–visible (UV–vis) spectrophotometer, X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), dynamic light scattering (DLS), and zeta potential analysis. The results of SEM revealed that NPs were irregular and spherical-shaped, with a diameter between 5 and 27 nm. Meanwhile, DLS supported that the measured size distributions were 202.8 and 94.7 nm at 11.1° and 90.0°, respectively, which supported the polydisperse nature of NPs, and the corresponding zeta potential was −20.4 mV. The insecticidal activity of the produced ZnO-NPs was determined against the adult stage of coleopteran pests, Sitophilus oryzae (Linnaeus) (Curculionidae) and Tribolium castaneum (Herbst) (Tenebrionidae). The LC₅₀ values of ZnO-NPs against adults of S. oryzae and T. castaneum at 24 h of exposure were 7125.35 and 5642.65 μg/mL, respectively, whereas the LC₉₀ values were 121,824.56 and 66,825.76 μg/mL, respectively. Moreover, the biosynthesized nanoparticles exhibited antibacterial activity against three potato bacterial pathogens, and the size of the inhibition zone was concentration-dependent. The data showed that the inhibition zone size increased with an increase in the concentration of nanoparticles for all bacterial isolates tested. The highest inhibition zone was observed for Ralstonia solanacearum at a concentration of 5 µg/mL, followed by Pectobacterium atrosepticum and P. carotovorum. Eventually, ZnO-NPs could be successfully used as an influential agent in pest management programs against stored-product pests and potato bacterial diseases.

Nanoparticles effectively control most plant pathogens, although research has focused more on their antimicrobial than their nematocidal properties. This study synthesized silver nanoparticles (Ag-NPs) through a green biosynthesis method using an aqueous extract of Ficus sycomorus leaves (FS-Ag-NPs). The nanoparticles were characterized using SEM, TEM, EDX, zeta sizer, and FTIR. The TEM results showed that the synthesized NPs were nanoscale and had an average particle size of 33 ± 1 nm. The elemental silver signal at 3 keV confirmed the formation of Ag-NPs from an aqueous leaf extract of F. sycomorus. The FTIR analysis revealed the existence of several functional groups in the prepared Ag-NPs. The strong-broad band detected at 3430 cm⁻¹ indicated the stretching vibration of -OH (hydroxyl) and -NH₂ (amine) groups. The nematocidal activity of biosynthesized FS-Ag-NPs has been evaluated in vitro against the root-knot nematode Meloidogyne incognita at 24, 48, and 72 h. The FS-Ag-NPs at a 200 µg/mL concentration applied for 48 h showed the highest effectiveness, with 57.62% nematode mortality. Moreover, the biosynthesized FS-Ag-NPs were also tested for their antibacterial activity against Pectobacterium carotovorum, P. atrosepticum, and Ralstonia solanacearum. With the application of nanoparticles, the reduction in bacterial growth gradually increased. The most potent activity at all concentrations was found in R. solanacearum, with values of 14.00 ± 2.16, 17.33 ± 2.05, 19.00 ± 1.41, 24.00 ± 1.41, and 26.00 ± 2.83 at concentrations of 5, 10, 15, 20, and 25 µg/mL, respectively, when compared with the positive control (Amoxicillin 25 µg) with a value of 16.33 ± 0.94. At the same time, the nanoparticles showed the lowest reduction values against P. atrosepticum when compared to the control. This study is the first report on the nematocidal activity of Ag-NPs using F. sycomorus aqueous extract, which could be a recommended treatment for managing plant-parasitic nematodes due to its simplicity, stability, cost-effectiveness, and environmentally safe nature.