Plant-mediated engineered nanomaterials (ENMs) synthesis is, low-cost, low-temperature, rapid, green technology using safe solvents (Chung et al., 2016; Munir et al., 2021). Palithya et al. (2021) used leaves of Decaschistia crotonifolia to synthesize silver (Ag) ENMs; combining the first leaf extract with silver nitrate (AgNO₃) in a 1:2 ratio changed the solution color from yellowish light green to dark brown. The antimicrobial activity of the synthesized ENMs was analyzed against gram-positive Staphylococcus aureus, Bacillus subtilis, Klebsiella pneumoniae and Escherichia coli. The biosynthesized ENMs exhibited better antibacterial activity against all bacterial species; while moderate efficacy compared to the standard antibiotic Amoxyclavhr. These ENMs had optimum catalytic activity to enhance the dye degradation rate by rapid reduction of nitrophenol to aminophenol. Hence, these ENMs could be used in various pharmaceutical and industrial applications. Hemlata et al. (2020) used leaf extract of Cucumis prophetarum to synthesize silver (Ag) ENMs. The plant extract was mixed in a 1:9 ratio with 0.001 M AgNO₃ solution. The mixture was heated at 80°C. The precipitates were then centrifuged and dried to obtain brown-colored silver (Ag) ENMs. The antimicrobial activity of the green-synthesized Ag ENMs and aqueous leaf extract of C. prophetarum was analyzed against Gram-positive Staphylococcus aureus and Gram-negative S. typhi; the ENMs showed greater antibacterial activity against Gram-negative than Gram-positive bacteria. The antiproliferative activity of the green-synthesized Ag-ENMs against cancer cell lines was also tested, with cell viability gradually decreasing with increasing concentration of Ag-ENMs. Figure 3 shows ENM synthesis using Salvia spinosa.

Khaldari et al. (2021) synthesized copper (II) oxide (CuO) ENMs using lavender and green tea leaves. Copper sulfate (CuSO₄.5H₂O) and lavender (or green tea) powder were mixed in varying proportions, with the resulting mixture ground into a homogeneous powder, heated at 600°C for 4 hours, and then cooled to room temperature before suspending the residue in ethanol and centrifuging to obtain the required ENMs. Figure 4 shows scanning electron microscopy (SEM) images of the nanomaterials. The X-ray diffraction (XRD) of green synthesized CuOENMs revealed that increasing the plant powder increased the purity of ENMs, and lavender powder produced more pure CuO ENMs than green tea leaf. Compared with chemically synthesized CuO ENMs, the biosynthesized ENMs had a less inhibitory effect on seed germination. Also, green and chemically synthesized CuO ENMs at low concentrations (i.e., 4 μg mL^–1) increased root and shoot lengths of lettuce and tomato seedlings (Khaldari et al., 2021).

Abutilon indicum leaf extract was used to synthesize CuO ENMs using the green combustion method (Ijaz et al., 2017). A homogeneous solution of copper (II) nitrate trihydrate and 0.3 g Abutilon indicum was prepared in 20 mL distilled water, heated at 400°C in a muffle furnace to form CuO ENMs, which were filtered and washed to remove impurities. The XRD results of the synthesized CuO ENMs revealed a highly crystalline structure due to the leaf extract, which controls particle size. Furthermore, the antimicrobial activity of the CuO the green ENMs was analyzed against S. aureus, Klebsiella, and B. subtilis by measuring the radius of inhibition zones, it was observed that the highest inhibition was observed for B. subtilis with 15 mm inhibition zone. When compared with the standard drug ampicillin, the CuO ENMs exhibited strong antimicrobial activity with a minimum inhibitory concentration (MIC) of 0.05 mg mL^–1, revealing that the CuO ENMs released copper (Cu) ions which penetrated the bacterial cell membrane, damaging its formation by attaching to negatively charged cell walls.

Ahmad et al. (2021) synthesized iron oxide ENMs using E. hirta leaf. The leaf extract was combined with 0.1 M ferrous sulfate heptahydrate and 0.1 M ferric chloride at constant pH 9 using standard sodium hydroxide (NaOH) solution; brown-colored iron-oxide ENMs formed after 3 h, which were centrifuged to remove impurities. The antimicrobial activities of the engineered ENMs were analyzed by quantifying the size inhibition zone on agar plates and determined to be directly proportional to their concentration. Erci and Cakir-Koc (2021) synthesized iron oxide ENMs (FeO) using T. spicata. The solution was formed by mixing T. spicata in 100 mL water, heated at 60°C for 30 min, and filtered. The extract was mixed with 0.1 M ferrous sulfate (FeSO₄.7H₂O) to synthesize iron oxide nanomaterials. The antimicrobial activity of the FeO ENMs was analyzed for Gram-positive and Gram-negative bacterial species. B. cereus had MIC and minimum bactericidal concentration (MBC) values of 200 mg mL^–1, and S. typhimurium had the lowest MIC of 100 mg mL^–1. The inhibition percentage was directly proportional to the fraction of leaf extract used to synthesize ENMs. The cytotoxicity of FeO ENMs on L929 cells was less than that for FeSO₄.7H₂O. Table 1 lists more examples of ENM synthesis using plant extracts

Algae are readily available and eco-friendly, with rich source of metabolites and optimum metal uptake capacity for use as reducing agents for nanoparticle synthesis (Abideen et al., 2022; Hasnain et al., 2022). In addition, algae accumulate higher lipids and potential source of biodiesel using saline lands and brackish water. Aboelfetoh et al. (2017) synthesized silver ENMs using Caulerpa serrulata from the Red Sea coast, Egypt. First, the algae were powdered after cleaning and natural drying; 1 g algae powder was cooked in 100 mL water for 10 min at 70°C before mixing 5–25 mL C. serrulata extract with 10⁻³ M AgNO₃ and adjusting the total volume to 100 mL. The formation of ENMs was depicted by yellow to brown color depending on the algal extract used, reaction time, temperature, and pH of the solution. The catalytic activity of the Ag-NP was evaluated in a reducing aqueous solution of Congo Red dye in the presence of sodium borohydride (NaBH₄) at room temperature. It was observed that without Ag ENMs no dye degradation was observed even after 3 hours, once biosynthesized Ag ENMs have added dye degradation started within 5 minutes. The antibacterial activity of the Ag-NP increased with increasing concentration of Ag-NP. The highest inhibition tendency occurred for E. coli, and minimum inhibition occurred for S. typhi. Dhas et al. (2013) synthesized silver chloride (AgCl) ENMs from Sargassum plagiophyllum. The seaweed was washed to remove impurities and dried in the shade for 8-10 days before grinding to a powder. A seaweed extract was prepared by mixing 5 g seaweed powder with 50 mL water. To synthesize AgCl ENMs, varying amounts of seaweed extracts (50-500 × 10^–6 L) were mixed with 5 mL of 0.001 M AgNO₃ solution and kept at room temperature for 1 day. The AgCl ENMs were depicted as yellowish-brown, spherical shapes (18-42 nm) in TEM images. The antibacterial activity of the AgCl ENMs was investigated against E. coli. The inhibitory action proportional to the quantity of AgCl ENMs, as depicted by larger inhibition zones was observed. Abboud et al. (2014) used Bifurcaria bifurcata (brown algae) to synthesize copper ENMs. The algae were washed with water (until it neutralized to pH 7), dried for 12 h at 60°C), and ground to a powder. The powder was boiled in water (1:5 ratio) for ~1 h, mixed with 0.001 M copper sulfate solution (1:10 ratio), and heated at about 100°C under continuous stirring to obtain dark brick red colored precipitates. The formation of spherical copper oxide ENMs (5-45 nm) was depicted in TEM images, with a few elongated ENMs (Figure 5). The antimicrobial activity of the copper oxide ENMs was considerable for Gram-negative and Gram-positive bacterial species (E. aerogenes and S. aureus) compared to the algae extract which had no antimicrobial activity.

Eroglu et al. (2013) synthesized spherical palladium nanocrystals from green microalgae (Chlorella vulgaris) using aqueous sodium tetrachloro-palladate Na₂ (PdCl₄) photosynthetic reactions. The nanocrystals were embedded in electrospun chitosan mats as a catalyst for the Mizoroki–Heck cross-coupling reaction. Cross-linked chitosan mats (3 × 2 cm rectangular shape) developed by electrospinning were dipped into a one-month-old mature microalgal culture in 25 mg L^–1 Na₂ (PdCl₄). The control sample comprised chitosan mats treated with 25 mg L^–1 Na₂ (PdCl₄) solution without microalgae. The efficacy of the biogenic nano palladium-chitosan mats was analyzed as catalyst support in the Mizoroki-Heck reaction. Six dried catalyst mats were placed into a solution containing iodobenzene, butyl acrylate, triethylamine and dimethylformamide (DMF) at 80°C for 16 h; after each reaction, the catalyst was recovered for regenerative studies after washing with DMF under nitrogen gas to prevent oxidation that may lead to the reproduction of Pd (0) ENMs. The catalyst was recyclable for a minimum of four reactions, with reaction yields of 68, 62, 45, and 36% (by weight) for the first to fourth cycles, respectively, much higher than the control at only 5%.

Ishwarya et al. (2018) synthesized zinc oxide (ZnO) ENMs using Ulva lactuca marine seaweeds. The seaweed was washed with water, cut, and dried in the air. A 10% solution of seaweed powder (5 g powder in 50 mL water) was obtained after boiling for 20 min. The extract was filtered and stored for later use when 5 mL extract was mixed with a 95 mL aqueous solution of 1 mM zinc acetate at 70°C with continuous stirring for 3-4 h. After centrifugation at 4,000 rpm for 10 min, yellowish-white precipitates were collected and washed with water before heating at 450°C for 4 h. Agglomerates of sample sponge-like asymmetrical shaped ENMs (10-50 nm) were depicted in TEM images. The inhibition percentage of antibacterial activity of ZnO ENMs against Gram-positive and Gram-negative species was observed between 80 to 95% in dark and visible light; specifically, lactuca-fabricated ZnO ENMs had an 82% reduction rate for B. licheniformis, 84% for B. pumilus, 80% for E. coli, and 79% for P. vulgaris (79%). Furthermore, the highest inhibition percentage of 100% occurred for A. aegypti in 50-μg mL^–1 ZnO ENMs at 24 h.

Fungi include many multicellular and unicellular species that used in various processes since early civilization. They play an important role in ecosystems, regulating the never-ending cycle of greenhouse gas emissions. Fungi have positive and negative impacts on our daily lives (Hussin, 2018). They are used in many industrial processes, including manufacturing antibiotics, steroids, and hormones (e.g., penicillin and cephalosporin), fermentation processes, organic acids (e.g., citric acid), and protein and vitamin production. While fungi cause many plant diseases for crops, several species improve soil quality and health, helping plants cope with saline and drought stresses (Ramasamy, 2020). Many fungal species used as protein-rich foods, including some mushrooms, morels, and truffles. Fungi can decompose all materials except plastics. Various fungal species are present in forest soils, withstanding stresses such as changing pH, decomposing cellulose lignin and other organic residues, and importing nutrients through hyphae for plant uptake of nitrogen, phosphorus, micronutrients, and water (Morris, 2004). Due to their rapid growth, simple synthesis, and short life cycle, fungi used in microbiology, biochemistry, and genetic engineering labs to study various metabolisms (e.g., the ‘one gene, one enzyme’ theory in Neurospora for which George W Beadle and Edward L Tatum won the Nobel Prize for Physiology or Medicine in 1958).

Yeasts are single-celled fungi widely used in various fermentation processes. The synthesis of ENMs through yeast simplifies the fermentation process, at ambient temperature; it is also very low cost and environmentally friendly. Moreover, synthesis through yeast has an advantage over other microbial species because yeast is the highest industrially produced microorganism in the world for different fermentation-based products, such as wine and bread. Bao et al. (2010) synthesized cadmium telluride quantum dots using yeast cells grown on a modified Czapek’s medium (450 g sucrose, 15 g sodium nitrate (NaNO₃), 5.0 g potassium hydrogen phosphate (K₂HPO₄), 2.5 g potassium chloride (KCl), 2.5 g magnesium sulfate (MgSO₄.7H₂O), and 30.0 g sodium citrate tribasic dihydrate dissolved in 5 L deionized water) and incubated for 2 days at 35°C. The yeast culture was combined with 400 mL cadmium chloride (CdCl₂) (0.04 mol L^–1), and 100 mL sodium tellurite (Na₂TeO₃) (0.04 mol L^–1), 7.5 g MSA, and 5.0 g NaBH₄, and incubated in a water bath. The final product comprised well-dispersed crystalline CdTe ENMs in a cubic zinc-blended shape (3.6 nm) after centrifugation dialysis using a dialysis membrane to remove residual chemicals and yeast cells.

Fernández et al. (2016) synthesized Ag ENMs using Cryptococcus laurentii and Rhodotorula glutinis incubated at 28°C and 100 rpm for 24 h in Muller–Hinton broth (MHB), containing 2 g beef infusion, 17.5 g acid casein peptone, and 1.5 g corn starch at neutral pH, with 2.0×10⁶ yeast cells in suspension and centrifuged before further use. The Ag ENMs were synthesized by adding 1 mL of 1 mM aqueous silver nitrate solution in 100 mL of yeast culture and stirring at 100 rpm at 28°C for 48 h in the dark. Particle formation (15-220 nm) was validated by the solution changing from yellow to deep brown using TEM images. Many fungi species rot fruits and vegetables and ultimately reduce their shelf life; therefore, the inhibition ability of biosynthesized Ag ENMs was assessed for B. cinerea, P.expansum, A. niger, Alternaria sp., and Rhizopus sp; the synthesized Ag ENMs from R. glutinis had higher antimicrobial activity than from C. laurentii. At 3 ppm, the ENMs synthesized from R. glutinis had antifungal efficacy comparable to antifungal agent iprodione against all fungi species in question (except Rhizopus). Eugenio et al. (2016) synthesized silver and silver chloride using yeasts produced from the gut of ten termites (Cornitermes cumulans). The gastrointestinal matter was placed on Sabouraud agar plates and incubated at 28°C for 48 h. For the incubation of separate clones, the colonies were re-incubated after dilution. Fifteen of these separate clones were used to synthesize AgCl ENMs; each isolated plate was inoculated in a liquid medium containing 4% glucose, 1% peptone, and 1% yeast extract at pH 6.5 at 30°C for 24 h. The media was mixed with 3.5 M silver nitrate solution and further incubated at 30°C in the dark with constant stirring at 150 rpm for 7 days. The silver chloride ENMs were separated from the mixture by centrifugation to obtain circular ENMs (2–10 nm), as confirmed by TEM images. To analyze the cell inhibition efficacy of biosynthesized silver chloride ENMs against S. aureus and K. pneumoniae, the ENMs were suspended in stabilizing solution comprising 1% sodium citrate with a basic pH 8 for 24 h. A dose-dependent inhibition effect was observed against both bacterial species at a maximum loading of 50μg mL^–1 (83% and 85% against S. aureus and K. pneumonia, respectively).

Tian et al. (2010) synthesized mesoporous zirconium phosphate using yeast grown in 100 mL of aqueous glucose solution (2 wt.%) at room temperature for 0.5 h before adding 3.2 g zirconyl chloride (ZrOCl₂.8H₂O). After 12 h, 100 mL of 0.2 M disodium hydrogen phosphate was mixed into the solution, maintaining the pH at 1-3 using 0.05 M HCl. After 2 h of mixing, a white gelatinous texture formed; after 48 h of storage, the mixture was centrifuged and washed vigorously with water and then ethanol. The product was dried at 80°C for 24 h to obtain a wormhole-like mesoporous structure from agglomerates of zirconium phosphate ENMs, which were analyzed for their efficiency as air electrodes for electro-catalytic activity in the oxygen reduction reaction (ORR) in alkaline solution. Due to its open mesoporous structure that can enhance mass transfer and neutralize polarization, this process had superior results to electrolytic manganese dioxide (EMD) air electrodes. These results showed that these mesoporous particles could be used for fuel cell applications.

Kanmani and Lim (2013) synthesized silver ENMs using a lactic acid bacterium that acts as a reducing and stabilizing agent. First, exopolysaccharide (EPS) was produced using bacterium: Lactobacillus rhamnosus GG was incubated in 1 L MRS (De Man, Rogosa, and Sharpe) agar broth at 37°C for 18 h and then heated at 100°C for 15 min to deactivate EPS-degrading enzymes before centrifuging to remove probiotic cells and debris. The supernatant was mixed with ethanol (95%) and cooled at 4°C for 12 h. The EPS precipitates were collected and washed with distilled water before mixing 20 mL EPS with 9 mM AgNO₃. The mixture was stored for 60 days in the dark; a 10 h incubation resulted in a yellowish solution, indicating the formation of silver ENMs, with sizes ranging from 2-15 nm and shapes ranging from the spherical, hexagonal, rod, and triangular. The antimicrobial activity of biogenic silver ENMs was dose-dependent against E. coli, L. monocytogenes (food-borne pathogen), and multi-drug resistant pathogens K. pneumonia and P. aeruginosa. P. aeruginosa had the highest inhibition zones, while the growth of L. monocytogenes was only inhibited at high nanoparticle doses (i.e., 2 mg mL^–1). Likewise, the efficacy of synthesized ENMs was dose-dependent against fungal pathogens Aspergillus spp. and Penicillium spp., particularly for Aspergillus spp. He et al. (2007) synthesized gold ENMs using the photosynthetic bacterial species Rhodo-pseudomonas capsulate by first maturing in a growth medium comprising pyruvate yeast extract, sodium chloride, ammonium chloride, and potassium hydrogen phosphate at pH 7 at 30°C for 3 days and then centrifuging to remove residual impurities. After washing with water, 1 g of the bacteria was mixed in 20 mL of 1×10⁻³ M chloroauric acid, neutralizing the pH with 0.1 M NaOH and 0.1 M HCl. As confirmed by TEM images, UV-visible spectra confirmed the nanoparticle synthesis with spherical ENMs (10–20 nm). Hence, synthesis of ENMs using microbial species is a time-efficient, ecofriendly, simple process that produces particles of uniform shape and size. Table 2 summarizes research studies using microbes to synthesize ENMs.

Seed germination and seedling growth are the backbones of crop yield and productivity (Zulfiqar, 2021). Seed priming is a technique used to improve the quality of seeds and their tolerance to environmental stresses. Priming seeds with nanomaterials is a novel method to increase germination rates and decrease seed aging (Itroutwar et al., 2020). The effect of bulk zinc acetate and algal synthesized zinc oxide (ZnO) ENMs on maize seed germination and plant growth. Maize seeds primed with varying concentrations of ZnO ENMs significantly improved the percentage of early seed germination compared to bulk zinc acetate and hydro primed (control) seeds. The 100 mg L^–1 ZnO treatment produced the highest germination percentage (87%) after one-week and the highest root and shoot lengths and widths. Panda (2017) soaked rice (Oryza sativa L.) in zinc nanoparticle solutions (5-50 mg L^–1) for 1 h under continuous stirring in an incubator. Seeds primed with Zn particles had longer radicles and plumules, higher radical and plumule fresh and dry weights, and higher relative water contents (RWC) of radices and plumules than untreated seeds. Mohammed et al. (2019) observed the effect of silica ENMs (SiO₂) at varying concentrations (100-300 mg L^–1) on the growth parameters of cucumber seeds. At 200 and 300 mg L^–1, silica-primed seeds reached 100% germination in 10 days. Seed priming also decreased the mean germination time from 4.1 days (no priming) to 2.8 days (200 mg L^–1). Siddiqui and Al-Whaibi (2014) examined the effect of SiO₂ ENMs (0–10 g L^–1) on the germination characteristics of tomato seeds (L. esculentum Mill. cv. Super Strain B). Seed germination increased with increasing SiO₂ concentration, peaking at 8 g L^–1.

Baz et al. (2020) observed the effect of carbon ENMs (CENMs) under saline conditions on the seed germination characteristics of different lettuce species. Lettuce seeds were primed with a 0.3% (wt) solution of CENMs (90–110 nm) for 2–14 h, followed by washing with water and then salt solution before incubating for 9 h. For the salt treatment, seeds were primed with 150-250 mM NaCl for 4 h. The CENMs pretreatment significantly reduced the adverse effects of saline and hot conditions on seed germination. Even 2 h of CENMs priming improved seed resistance to saline, with germination rates reaching 100% compared to only 10% under saline conditions without no CENMs treatment also the germination rates of seeds under thermal stress of 34°C were observed to enhance in seeds primed with CENMs up to 90% as compared to 405 without CENMs. Only a few species had very low germination rates, even after priming for 10 h. Table 3 lists some studies using ENMs for seed priming and germination.

Nanomaterials can alter plant growth through nutrient uptake, improving capacity, resistance against biotic and abiotic stresses, promoting nitrogen metabolism, osmotic protection, and plant defense against pathogens. The conventional application of nutrients to the soil has several disadvantages in terms of nutrient availability to plants. Therefore, the foliar application is the most efficient method of compensating for nutrient deficiencies and increasing crop yield and quality. Foliar spraying also reduces environmental contamination and increases nutrient use efficacy by decreasing the amount of fertilizer applied to the soil. Biologically engineered ZnO ENMs have been used as a low-cost biomass-enhancing agent for crop plants (Venkatachalam et al., 2017). The effect of 25-200 mg/L of ZnO ENMs and phosphorous on cotton seeds was analyzed in growth stimulation experiments. Root and shoot lengths, total biomass, and the growth tolerance index were directly proportional to the concentration of (200 mg L^–1) zinc oxide ENMs. Rizwan et al. (2019) addressed the effect of zinc and iron ENMs on wheat’s growth characteristics and capacity to accumulate cadmium (Cd) (Triticum aestivum). Wheat seeds were primed for one day with different concentrations of ZnO (25-100 mg L^–1) and FeO (5-20 mg L^–1). After priming, the seeds were grown in Cd-contaminated soil. Primed seeds produced more healthier plants than unprimed seeds as plant height, shoot and spike lengths, and plant dry weight were directly proportional to the concentrations of Zn and Fe ENMs. Sun et al. (2020) observed growth parameters of tomato plants sprayed with 20-100 mg L^–1 ZnO ENMs; the foliar sprayed plants had greater plant heights, root lengths, and chlorophyll contents than the unsprayed plants. In addition, plant mineral and nutrient contents (calcium, magnesium, sucrose, starch and glucose) increased, significantly increasing iron deficiency tolerance.

Song et al. (2012) analyzed the effect of 10-2000 mg/L of Titanium dioxide (TiO₂) ENMs and bulk TiO₂ on the growth parameters of Lemna minor. For nanoparticle TiO₂ concentrations <500 mg L^–1, plant growth (root length, fresh weight, and frond number) had a directly proportional relationship with TiO₂ concentration; a similar trend occurred for bulk TiO₂ but to a lesser degree than the ENMs. The same growth parameters decreased at nanoparticle concentrations ≥500 mg L^–1. Daghan (2018) analyzed the effect of TiO₂ ENMs (25-100 mg L^–1) on the seedling growth of maize irrigated with wastewater. The 25 mg L^–1 treatment inhibited the adverse effects of wastewater and reached 100% seed germination, while higher doses had adverse effects on the seed germination rate. Liu and Lal (2014) used hydroxyapatite ENMs on soybean (see Figure 7). All growth parameters (growth rate, plant height, seed yield, aboveground and belowground biomass) increased compared to conventional phosphorus fertilizer.

Khan et al. (2021) analyzed the efficiency of silver ENMs (10-30 mM) for enhancing the growth of pearl millet under saline conditions (up to 150 mM NaCl). Adding ENMs under saline conditions significantly increased plant growth, including plant height, root, shoot, and dry grain weights, chlorophyll content, and photosynthetic rate. Suciaty et al. (2018) analyzed the effect of nano-silica (1.25-3.75 mL L^–1) and rice hull ash (1-3 t ha^–1) on the growth characteristics of Grobogan, a soybean cultivar. Rice hull ash increased plant height, but silica ENMs had no effect; silica ENMs and rice hull ash increased dry seed weight after applied individually. Table 4 lists other studies using ENMs for plant growth applications.

Nanomaterials extensively used to alleviate plant diseases, as many nanomaterials have inhibitory effects against disease-causing microorganisms. Nanomaterials can also increase the yield of fruit-bearing plants by fulfilling their nutrient requirements or catalyzing photosynthesis. Hernández-Hernández et al. (2017) evaluated the effect of copper ENMs (0.02-10 mg) embedded in chitosan-polyvinyl alcohol (Cs-PVA) hydrogels on the growth, productivity, and fruit quality of tomato plants. Growth parameters (stem diameter, stem, root, and leaf weights, flower bunches per plant, leaf number per plant, and yield) increased with nanoparticle treatment. (Xing et al. 2021) observed dose-dependent antimicrobial activity of oleoyl-chitosan (O-chitosan) ENMs against several plant pathogenic fungi. Four fungal species (N. sphaerica, B. dothidea, N. oryzae, and A. tenuissima) had significant growth inhibition at 2 mg mL^–1 O-chitosan. Sathiyabama and Manikandan (2018) Analyzed the efficacy of copper-chitosan ENMs (seed priming or foliar spray) on finger millet. The combined treatment i.e. seed priming and foliar spray, increased plant yield, chlorophyll content, and leaf quantity and decreased spore growth of Pyricularia grisea, which causes blast disease in millet. Hao et al. (2019) analyzed the efficacy of four engineered nanomaterials [multi-walled carbon nanotubes (MWCNTs), reduced graphene oxide (RGO), titanium dioxide (TiO₂), and copper oxide (CuO)] for fungal disease control in rose plants. The ENMs were suspended in water (50 or 200 mg L^–1) and sprayed on the leaves of rose plants infected with Podosphaera pannosa (P. pannosa), which causes powdery mildew disease (see Figure 8). After 19 days of 200 mg L^–1 treatment, RGO, MWCNTs, and TiO₂ ENMs had decreased the size of the infected area by 46%, 60%, and 70%, respectively. At 50 mg L^–1, no inhibitory affect was observed for these three materials. For CuO ENMs, the 50 and 200 mg L^–1 treatments decreased the infected area by 73% and 99%, respectively. Hao et al. (2018) analyzed the efficacy of four ENMs (TiO₂, Ferric oxide (Fe₂O₃), MWCNT, and fullerene) for antiviral activity and growth of tobacco (Nicotiana benthamiana) infected with turnip mosaic virus. A 50 or 200 mg L^–1 of each nanoparticle-water suspension was sprayed on tobacco leaves for 21 days. For the metallic ENMs, the maximum antiviral effect occurred at 50 mg L^–1, while MWCNT had an inhibitory effect at both doses, while Fullerene (C₆) had no antiviral activity. Similarly, the metallic ENMs increased fresh biomass by 56% at 50 mg L^–1, with no change at 200 mg L^–1. The 50 and 200 mg L^–1 treatment of MWCNTs and C₆₀ increased fresh biomass by 55%. Zahedi et al. (2019b) sprayed selenium ENMs embedded in sodium metal (Na₂SeO₄; 1-2 μM) on pomegranate leaves (Punica granatum L. cv. Malase Saveh) to evaluate their effect on growth characteristics and fruit quality. Plants sprayed with selenium ENMs had higher leaf surface area, chlorophyll content, and fruit numbers than unsprayed plants; the 2 μM treatment increased fruit yield/plant by 35%, peel thickness by 33.6%, fruit weight by 5.2%, fruit length by 30%, and fruit diameter by 11%, and decreased the fruit cracking percentage by 54%. Nandini et al. (2017) analyzed the efficacy of a foliar spray of selenium (mediated with Trichoderma) ENMs against downy mildew disease (Sclerospora graminicola) in pearl millet. Different species of Trichoderma were used; T. asperelleum combined with Se ENMs had the best results against downy mildew disease, with a MIC of 150 ppm. Similarly, seed priming with T. asperelleum-mediated Se ENMs improved plant height, tiller number per seedling, dry weight, and chlorophyll content. Joshi et al. (2021) used myogenic selenium ENMs to prime tomato seeds and analyzed their efficacy against late blight disease; the Se-primed seeds inhibited the disease by 73%, increased plant height by 51% and fruit weight by 83%, and expedited flower emergence from 70 days (unprimed) to 61 days.

Kumari et al. (2017) applied green-synthesized silver ENMs (5 μg mL^–1) to tomato as an antidote for early blight disease (Alternaria solani). Three days of treatment eliminated the spore count. The silver ENMs treatment increased fresh and dry weights of leaves by 32 and 23%, respectively, Chlorophyll a by 14%, Chlorophyll b by 50%, total chlorophyll by 23%, and carotenoid content by 20%. Quiterio-Gutiérrez et al. (2019) sprayed selenium and copper ENMs on tomato leaves infected with Alternaria solani, which increased the number of fruit clusters per plant by 9%. Table 5 lists other ENM applications for plant disease inhibition and fruit yield enhancement.