anti-TMV Activity Research Articles

Facile synthesis, crystal structure, quantum calculation, and biological evaluations of novel selenenyl sulfide compounds as potential agrochemicals.

In order to design compounds with fresh molecular skeleton to break through the limitation of available agrochemicals, a series of 36 novel selenenyl sulfide compounds were chemically synthesized, and their biological activities were fully evaluated against tobacco mosaic virus (TMV), 14 plant pathogenic fungi, three insect species and plant acetohydroxyacid synthase (AHAS). All the target compounds were characterized by proton nuclear magnetic resonance (1 H-NMR), carbon-13 (13 C)-NMR, selenium-77 (77 Se)-NMR, and high-resolution mass spectrometry (HRMS). The crystal structure of 10j indicated that the Se-S bond was successfully constructed. Compounds 10d, 10h, 10s, 10u, 10aa, 10ac, 10ae, 10ag, and 10ai exhibited 40%, 43%, 39%, 41%, 47%, 46%, 47%, 42%, and 39% anti-TMV activities at 500 mg L-1 , better than that of ribavirin. The median effective concentration (EC50 ) against Sclerotinia sclerotiorum of 10ac was 6.69 mg L-1 and EC50 values against Physalospora piricola and Pyricularia grisea of 10z were 12.25 mg L-1 and 15.27 mg L-1 , respectively, superior to the corresponding values of chlorothalonil. Compounds 10c and 10v demonstrated 100% larvicidal activity against Culex pipiens pallens at 5mg L-1 , while 10a displayed 100% insecticidal activity against Mythimna separata at 200 mg L-1 . Compounds 10c, 10j, and 10o showed > 60% inhibitions against plant AHAS at 10μmol L-1 . From the quantum calculation, highest occupied molecular orbital (HOMO) was considered as a factor that affects the anti-TMV activity. The preliminary results suggested that more efforts should be devoted to exploring the selenenyl sulfides for the discovery of new leads of antiviral agent, fungicide, insecticide or AHAS inhibitors as potential agrochemicals for crop protection. © 2023 Society of Chemical Industry.

Design, Synthesis and Bioassay of 2-Phenylglycine Derivatives as Potential Pesticide Candidates.

Plant diseases can seriously affect the growth of food crops and economic crops. To date, pesticides are still among the most effective methods to prevent and control plant diseases worldwide. Consequently, to develop potential pesticide molecules, a series of novel 2-phenylglycine derivatives containing 1,3,4-oxadiazole-2-thioethers were designed and synthesized. The bioassay results revealed that G19 exhibited great in vitro antifungal activity against Thanatephorus cucumeris with an EC50 value of 32.4 μg/mL, and in vivo antifungal activity against T. cucumeris on rice leaves at a concentration of 200.0 μg/mL (66.9 %) which was close that of azoxystrobin (73.2 %). Compounds G24 (80.2 %), G25 (89.4 %), and G27 (83.3 %) exhibited impressive in vivo inactivation activity against tobacco mosaic virus (TMV) at a concentration of 500.0 μg/mL, which was comparable to that of ningnanmycin (96.3 %) and markedly higher than that of ribavirin (55.6 %). The antibacterial activity of G16 (63.1 %), G26 (89.9 %), G27 (78.0 %), and G28 (68.0 %) against Xoo at a concentration of 50.0 μg/mL was higher than that of thiadiazole copper (18.0 %) and bismerthiazol (38.9 %). Preliminary mechanism studies on the antifungal activity against T. cucumeris demonstrated that G19 can affect the growth of mycelia by disrupting the integrity of the cell membrane and altering the permeability of the cell. These studies revealed that the amino acid derivatives containing a 1,3,4-oxadiazole moiety exhibited certain antifungal, antibacterial, and anti-TMV activities, and these derivatives can be further modified and developed as potential pesticide molecules.

Structural Optimization of the Natural Product: Discovery of Almazoles C–D and Their Derivatives as Novel Antiviral and Anti-phytopathogenic Fungus Agents

Plant diseases seriously affect the growth of crops and the quality and yield of agricultural products. The search for plant-derived pesticide candidates based on natural products is a hot topic of current research. Marine natural products almazoles C-D were efficiently prepared and selected as the lead compounds in this work. Two series of almazole derivatives were designed and synthesized, and their antiviral and fungicidal activities were systematically evaluated. The results of anti-tobacco mosaic virus (anti-TMV) activity showed that almazoles C-D and their derivatives had good anti-TMV activities. Compounds 6, 15, 16a, 16b, 16g, 16l, 16n, 20a, 20d, 20i, and 20n exhibited better anti-TMV activities than the commercial antiviral agent ribavirin. Anti-TMV mechanism studies showed that compound 16b could induce the polymerization of 20S CP (coat protein, CP), thereby affecting the assembly of TMV virus particles. Molecular docking results showed that compounds 15, 16b, and 20n could combine with amino acid residues through hydrogen bonds to achieve an excellent anti-TMV effect. In addition, most of the almazole derivatives were found to have broad-spectrum fungicidal activities against eight kinds of plant pathogens (Fusarium oxysporum f. sp. cucumeris, Cercospora arachidicola Hori, Physalospora piricola, Rhizoctonia cerealis, Alternaria solani, Pyricularia grisea, Phytophthora capsici, and Sclerotinia sclerotiorum). This study provides an important evidence for the research and development of almazole alkaloids containing indole and oxazole structural groups as novel agrochemicals.

Antivirus isoindolinone alkaloids with rare oxocyclopenta[f]isoindole frameworks isolated from the stems of flue cured tobacco

BackgroundSince Nicotiana tabacum (tobacco) has important significance to humans for their medicinal uses, to find antivirus activities inhibitors from tobacco, increase its medicinal value, and comprehensive utilization of its by-products, our group had investigated the chemical constituents of the stems of Y-202, a cultivar of tobacco which high resistance to tobacco mosaic virus (TMV).ResultsFour new isoindolinone-type alkaloids, nicoisoindoles A–D (1–4), along with four known isoindole derivatives (5–8) were isolated. Compounds 1–4 represent a new subclass of isoindolinone alkaloids with rare cyclopenta[f]isoindole-1-one frameworks. Among them, nicoisoindole C (3) possesses an unusual N-2-(5-methoxy-6-methylpyridin-2-yl) ethyl moiety, while nicoisoindole D (4) has a novel a N-(3-methyl-6-oxo-1,6-dihydropyridin-2-yl)methyl substituent. Interestingly, compounds 1, 3, and 4 showed high anti-TMV activities with inhibition rates of 43.8%, 58.8%, and 67.8% at the concentration of 20 μM, and IC50 values of 23.6, 19.5 and 15.4 μM, respectively, even more potent than that of positive control.ConclusionsThe successful isolation and structure identification of new oxocyclopenta[f]isoindole-1-ones provide materials for the screening of antivirus activities inhibitors, and contribute to the development and utilization of the waste from tobacco cultivation.Graphical

The anti-TMV potency of the tobacco-derived fungus Aspergillus versicolor and its active alkaloids, as anti-TMV activity inhibitors

Nicotiana tabacum (tobacco) has attracted interest as one of the most economically important industrial crops widely cultivated in China, whose dried leaves are popularly consumed medicinally and recreationally by human societies. In this study, five undescribed alkaloids derivatives, isoaspergillines A–E, together with eight known alkaloids, notoamide D, (1R,4S)-4-benzyl-1-isopropyl-2,4-dihydro-1H-pyrazino-[2,1-b]quinazoline-3,6-dione, protuboxepin K, notoamide C, notoamide M, deoxybrevianamide E, cyclo (D-Pro-L-Trp), and versicolamide B, were obtained from the culture of the Nicotiana tabacum-derived fungus Aspergillus versicolor. Their structures were mainly elucidated through comprehensive analyses of spectroscopic data. Bioactivity evaluation of all isolated compounds revealed that isoaspergilline A and notoamide M exhibited anti-TMV activities with IC50 values of 20.0 and 22.8 μM, respectively. Molecular docking suggested that isoaspergilline A and notoamide M were well located into the active site of anti-TMV by interacting with SER138, SER143, and ASN73 residues. This study enlightens the therapeutic potential of the endophytic fungus A. versicolor and it is helpful to find undescribed anti-TMV activity inhibitors, as well as searching for new anti-TMV candidates from natural sources.

Synthesis and Evaluation of 11-Butyl Matrine Derivatives as Potential Anti-Virus Agents.

Matrine derivatives were reported to have various biological activities, especially the ester, amide or sulfonamide derivatives of matrine deriving from the hydroxyl or carboxyl group at the end of the branch chain after the D ring of matrine is opened. In this work, to investigate whether moving away all functional groups from the C-11 branch chain could have an impact on the bioactivities, such as anti-tobacco mosaic virus (TMV), insecticidal and fungicidal activities, a variety of N-substituted-11-butyl matrine derivatives were synthesized. The obtained bioassay result showed that most N-substituted-11-butyl matrine derivatives had obviously enhanced anti-TMV activity compared with matrine, especially many compounds had good inhibitory activity close to that of commercialized virucide Ningnanmycin (inhibition rate 55.4, 57.8 ± 1.4, 55.3 ± 0.5 and 60.3 ± 1.2% at 500 μg/mL; 26.1, 29.7 ± 0.2, 24.2 ± 1.0 and 27.0 ± 0.3% at 100 μg/mL, for the in vitro activity, in vivo inactivation, curative and protection activities, respectively). Notably, N-benzoyl (7), N-benzyl (16), and N-cyclohexylmethyl-11-butyl (19) matrine derivatives had higher anti-TMV activity than Ningnanmycin at both 500 and 100 μg/mL for the four test modes, showing high potential as anti-TMV agent. Furthermore, some compounds also showed good fungicidal activity or insecticidal activity.

Synthesis and Biological Activity of Novel Oxazinyl Flavonoids as Antiviral and Anti-Phytopathogenic Fungus Agents.

A series of oxazinyl flavonoids were synthesized on the basis of flavone. The structures of all target compounds were characterized by 1H NMR, 13C NMR, and HRMS. The effect of the different substituent on the N-position of oxazinyl flavonoids against tobacco mosaic virus (TMV) activities and plant pathogen activities was systematically investigated. In vivo anti-TMV activity showed that most of the compounds showed moderate-to-excellent antiviral activities against TMV at 500 μg/mL. Compounds 6b, 6d, 6j–6k, and 6n–6q showed better antiviral activities than ribavirin (a commercially available antiviral agent) and apigenin. In particular, compounds 6n and 6p even displayed slightly higher activities than ningnanmycin, which were expected to become new antiviral candidates. Antiviral mechanism research by molecular docking exhibited that compounds 6n and 6p could interact with TMV CP and inhibit virus assembly. Then, the antifungal activities of these compounds against six kinds of plant pathogenic fungi were tested, and the results showed that these oxazinyl flavonoids had broad-spectrum fungicidal activities. Compounds 6h exhibited antifungal activity of up to 91% against Physalospora piricola and might become a candidate drug for new fungicides.

Two New CPA-Type Indole Alkaloids from the Tobacco-Derived Fungus Aspergillus versicolor and the Anti-TMV Activity

Two New CPA-Type Indole Alkaloids from the Tobacco-Derived Fungus Aspergillus versicolor and the Anti-TMV Activity

Antitobacco Mosaic Virus Activity of a New Eremophilane Glucoside From the Leaves of Nicotiana tabacum L

A new eremophilane-type sesquiterpene glucoside, 13-hydroxycapsidiol 3- O- β-D-glucoside (1), was isolated from the leaves of Nicotiana tabacum L. The structure of this new metabolite was determined by one-dimensional (1D) and 2D nuclear magnetic resonance (NMR) spectroscopy, high-resolution electrospray ionization mass spectrometry (HR-ESI-MS), and comparison with values reported in the literature. Compound 1 was the second glycosylated eremophilane sesquiterpenoid isolated from plants of the Solanaceae family and exhibited a more potent anti-tobacco mosaic virus (anti-TMV) activity, with an inhibition rate of 39.4% at 20 μM, than the positive control ningnanmycin (34.8%).

Discovery of Novel α-Methylene-γ-Butyrolactone Derivatives Containing Vanillin Moieties as Antiviral and Antifungal Agents.

On the basis of the structure of nicotlactone A (L1), a series of novel α-methylene-γ-butyrolactone derivatives B1-B43 were designed and synthesized by structure simplification and active fragment replacement strategies, and their antiviral and antifungal activities were evaluated. The bioassay studies indicated that many target compounds possessed good to excellent antiviral activity against tobacco mosaic virus (TMV) and some of these compounds exhibited specific antifungal activities against Valsa mali and Fusarium graminearum. Compound B32 exhibited the best anti-TMV activity (inactivation effect, 88.9%; protection effect, 65.8%; curative effect, 52.8%) in vivo at 500 mg/L, which is significantly higher than that of commercial virucides ribavirin and ningnanmycin. The inhibition effect of compound B32 was also visualized by the inoculation test using green fluorescent protein (GFP)-labeled TMV. The preliminary antiviral mechanism of compound B32 was investigated. Transmission electron microscopy (TEM) showed that compound B32 could destroy the integrity of virus particles. Then, molecular docking and isothermal titration calorimetry (ITC) analysis further demonstrated that compound B32 exhibited a strong binding affinity to the TMV coat protein with a dissociation constant (Kd) of 3.06 μM, superior to ribavirin. Thus, we deduced that compound B32 may interfere with the self-assembly of TMV particles by binding TMV coat protein (CP). In addition, compound B28 showed good in vitro activity against F. graminearum with an inhibition rate of 90.9% at 50 mg/L, which was greater than that of fluxapyroxad (59.1%) but lower than that of the commercial fungicide carbendazim (96.8%). The present study provides support for the application of these α-methylene-γ-butyrolactone derivatives as novel antiviral and antifungal agents in crop protection.

Isoindolin-1-ones from the stems of Nicotiana tabacum and their antiviral activities

In previous studies, several isoindolin-1-one analogs that exhibited significant anti-tobacco mosaic virus (anti-TMV) activities were isolated from Nicotiana tabacum. Since gene-editing mutants provide a new sample for the discovery of active metabolites, we focused on the stems of YN-18-23 (a mutant N. tabacum for gene editing with the alkaloid metabolic pathway cultivated by Yunnan Tobacco Company), which led to the isolation of four new (1-4) and four known (5-8) isoindolin-1-ones. To the best of our knowledge, nicindole C (3) is the first subclass of isoindolin-1-one bearing a pentacyclic ketone, while nicindole D (4) is the first example of isoindolin-1-one bearing a methyl-pyridin-2-(1H)-one moiety. Compounds 1-4 were tested for their anti-TMV activities, and the results revealed that compounds 1, 3, and 4 exhibited high anti-TMV activities at concentrations of 20μM with inhibition rates of 48.6, 42.8, and 71.5%, respectively. These rates are higher than the inhibition rate of the positive control (33.2%). The mechanistic study of compound 4, which had the highest anti-TMV activity revealed that increased potentiation of defense-related enzyme activities and downregulation of expression of the NtHsp70 protein may induce resistance in tobacco against the viral pathogen TMV. Molecular docking studies also revealed that the isoindolin-1-one substructure is fundamental for anti-TMV activity. The methyl-pyridin-2-(1H)-one moiety in compound 4 and the 2-oxopropyl groups in compounds 1 and 3 at the N-2 position may increase inhibitory activities. This study of the structure-activity relationship is helpful for finding new anti-TMV activity inhibitors. To study whether the isoindolin-1-ones have broader antiviral activities, compounds 1-4 were also tested for their anti-rotavirus activities. Compound 4 exhibited high anti-rotavirus activity with a therapeutic index (TI) value of 20.7. This TI value is close to that of the positive control (20.2).

Isochromenes from the Nicotiana tabacum-derived endophytic fungus Aspergillus versicolor and their anti-tobacco mosaic virus activities

Three new isochromenes, (5-methoxy-7-prenyl-1H-isochromen-3-yl)methanol (1), 3-(3-(hydroxymethyl)-5-methoxy-1H-isochromen-7-yl)propan-1-ol (2), and (5-methoxy-7-methyl-1H-isochromen-3-yl)methanol (3), along with three known analogues (4–6) were isolated from the fermentation products of a Nicotiana tabacum-derived endophytic fungus Aspergillus versicolor. Their structures were elucidated by spectroscopic methods, including extensive 1 D and 2 D NMR techniques. Compounds 1–3 and 6 were evaluated for their anti-tobacco mosaic virus (anti-TMV) activities. The results showed that compound 2 exhibited high anti-TMV activity with inhibition rate of 46.4%, and this rate is higher than that of positive control. Compounds 1, 3, and 6 also showed potential anti-TMV activity with inhibition rates of 28.6, 30.5, and 26.2%, respectively. The IC50 of compounds 1–3 and 6 were also tested, and showed IC50 values of 49.3, 22.4, 42.2, and 54.1 µM, respectively.

Two New CPA-Type Indole Alkaloids from the Tobacco-Derived Fungus Aspergillus oryzae and Anti-TMV Activity

Two New CPA-Type Indole Alkaloids from the Tobacco-Derived Fungus Aspergillus oryzae and Anti-TMV Activity

1,3,4-Oxadiazole Derivatives as Plant Activators for Controlling Plant Viral Diseases: Preparation and Assessment of the Effect of Auxiliaries.

Plant viral diseases cause the loss of millions of dollars to agriculture around the world annually. Therefore, the development of highly efficient, ultra-low-dosage agrochemicals is desirable for protecting the health of crops and ensuring food security. Herein, a series of 1,3,4-oxadiazole derivatives bearing an isopropanol amine moiety was prepared, and the inhibitory activity against tobacco mosaic virus (TMV) was assessed. Notably, compound A14 exhibited excellent anti-TMV protective activity with an EC50 value of 137.7 mg L-1, which was superior to that of ribavirin (590.0 mg L-1) and ningnanmycin (248.2 mg L-1). Moreover, the anti-TMV activity of some compounds could be further enhanced (by up to 5-30%) through supplementation with 0.1% auxiliaries. Biochemical assays suggested that compound A14 could suppress the biosynthesis of TMV and induce the plant's defense response. Given these merits, designed compounds had outstanding bioactivities and unusual action mechanisms and were promising candidates for controlling plant viral diseases.

The curative activity of some arylidene dihydropyrimidine hydrazone against Tobacco mosaic virus infestation

A series of novel pyrimidine-based derivative compounds were synthesized and evaluated for antiviral activity against Tobacco mosaic virus (TMV). All chemical structures of the prepared compounds were identified and characterized by IR, NMR, and elemental analysis. Under greenhouse conditions, the preliminary bioassays revealed that all compounds exhibited anti-TMV activity ranging from 23.5 % to 90.1% at 50 µg/mL concentration, indicating potential antiviral efficacy. Among the new compounds, the benzylidene derivative 3a was the most potent and demonstrated the highest inhibition effect of 90%, with a significant reduction in the TMV accumulation level of 91.4%. Furthermore, the curative activity of 3a was associated with a considerable decrease in H2O2 and MDA (nonenzymatic oxidative stress markers) compared to the TMV treatment. In addition, significant increases in the transcriptional levels of pathogenesis-related proteins (PR-1, PR-3, PR-4, and PR-5) at 4 and 6 dpi were shown to induce systemic resistance against TMV. Furthermore, molecular docking investigation demonstrated that the benzylidene derivative 3a was strongly lodged in the binding sites of TMV-coat protein at position 2.Consequently, the obtained results suggest that the new 3a compound could be applied as a safe control agent against plant viral infection.

Anti-TMV effects of seco-pregnane C21 steroidal glycosides isolated from the roots of Cynanchum paniculatum

Tobacco mosaic virus (TMV) is known to infect a wide range of plants, resulting in reduced yield and productivity. Novel, effective, and plant-based pesticides are required to protect plants against TMV infection. To identify novel anti-TMV agents from natural sources, we systematically studied the roots of Cynanchum paniculatum and isolated six new seco-pregnane C21 steroidal glycosides, along with 14 known compounds. Their structures were elucidated by comprehensive spectroscopic data analysis. The anti-TMV activity of compounds were screened using the half-leaf method. Biological tests revealed that compounds 1, 2, 5, 9, 10, 15, and 16 displayed significant anti-TMV activities compared with the positive control ningnanmycin. In addition, reverse transcription-polymerase chain reaction (RT-PCR) and western blot analysis confirmed the antiviral activity of these compounds, as evident from reduced TMV coat protein (TMV-CP) gene replication and TMV-CP protein expression. These compounds downregulated the expression of NtHsp70–1 and NtHsp70–261, indicating that these steroidal glycosides possibly inhibit the TMV infection by suppressing the expression of NtHsp70–1 and NtHsp70–061 expression.

Indole Alkaloids and Chromones from the Stem Bark of Cassia alata and Their Antiviral Activities.

The Cassia (Leguminosae) genus has attracted a lot of attention as a prolific source of alkaloids and chromones with diverse structures and biological properties. The aim of this study is to screen the antiviral compounds from Cassia alata. The extract of the stem bark of this plant was separated using silica gel, MCI, ODS C18, and Sephadex LH-20 column chromatography, as well as semi-preparative HPLC. As a result, three new indole alkaloids, alataindoleins A–C (1–3); one new chromone, alatachromone A (4); and a new dimeric chromone-indole alkaloid, alataindolein D (5) were isolated. Their structures were determined by means of HRESIMS and extensive 1D and 2D NMR spectroscopic studies. Interestingly, alataindolein D (5) represents a new type of dimeric alkaloid with an unusual N-2−C-16’ linkage, which is biogenetically derived from a chromone and an indole alkaloid via an intermolecular nucleophilic substitution reaction. Compounds 1–5 were tested for their anti-tobacco mosaic virus (TMV) and anti-rotavirus activities, and the results showed that compounds 2–4 showed high anti-TMV activities with inhibition rates of 44.4%, 66.5%, and 52.3%, respectively. These rates were higher than those of the positive control (with inhibition rate of 32.8%). Compounds 1 and 5 also showed potential anti-TMV activities with inhibition rates of 26.5% and 31.8%, respectively. In addition, compounds 1–5 exhibited potential anti-rotavirus activities with therapeutic index (TI) values in the range of 9.75~15.3. The successful isolation and structure identification of the above new compounds provided materials for the screening of antivirus drugs, and contributed to the development and utilization of C. alata.

Synthesis and Structure–Activity Relationship Studies of Nicot­lactone Analogues as Anti-TMV Agents

AbstractThe synthesis of the originally proposed structure of (±)-nicotlactone A, a potent antiviral lignan with three continuous chiral centers, is reported in 5 steps from methyl acrylate. The key steps of the synthesis included an In-catalyzed regioselective allylation and a Mn-catalyzed Mukaiyama hydration reaction. Our synthetic strategy also enabled us to get the other three epimers and investigate the structure–activity relationship. The NMR data of the synthesized compounds do not match that of the isolated sample, indicating that the structure of nicotlactone A remains to be reassigned. All the synthetic target compounds were evaluated for their anti-tobacco mosaic virus (anti-TMV) activity. Bioassay results indicated that (±)-8-demethylnicotlactone A displayed similar anti-TMV activity to the commercial agent ningnanmycin, thus being a promising candidate or lead compound for developing novel antiviral agents in crop protection.

Design, synthesis and biological activity of 4-amino-5-(Benzimidazole-1-yl) triazole

Triazoles are an important class of nitrogen containing heterocycles, because many of them exhibit interesting biological activities, such as anti-inflammatory, antidepressant, antifungal, anticancer,anti-TB, analgesic and hypoglycemic. Sulfur-linked 1,2,4-triazoles represent an important group in lead compound discovery. Many bioactive sulfur-linked 1,2,4-triazole have been reported, such as antibacterial activity, antitumor activity, anti-HIV activity, anti-TMV (tobacco mosaic virus) activity, and so on. We report Synthesis and Biological activity of 4-amino-5-(Benzimidazole-1-yl) Triazole.

Citral induces plant systemic acquired resistance against tobacco mosaic virus and plant fungal diseases

Litsea cubeba essential oil (LCO) has a wide range of industrial uses. This study found that LCO has significant anti-TMV activity and that its active components are monoterpenoids. Citral, the main active component of the oil, showed outstanding anti-TMV activity. The protective, inactive, and curative efficacies of citral (500 μg/mL) against TMV were 76.27%, 55.14%, and 50.42%, respectively, which were significantly better than those of the positive control agent, chitosan oligosaccharide. Citral showed no direct effect on TMV particles but did induce hypersensitive response (HR). Bioassay results showed that citral induced significant plant disease resistance activity (68.20% at a concentration of 500 μg/mL). The results of physiological and biochemical experiments showed that citral induced the overexpression of defense enzymes such as SOD, CAT, POD, and PAL in tobacco (which increased by 5.3, 1.9, 3.0, and 4.0 times at a concentration of 500 μg/mL, respectively) as well as induced the overexpression of PR proteins, including NPR1, PR1, PR2, and PR5 (which increased by 23.49, 39.27, 34.47, and 52.07 times at a concentration of 500 μg/mL, respectively). These results suggest that citral could induce systemic acquired resistance (SAR) in tobacco. Further mechanism studies conducted suggest that citral induces the overexpression of genes related to salicylic acid (SA) biosynthesis, including PAL, ICS, and PBS3 (50.74, 30.41, and 31.95 times higher than the control at a concentration of 500 μg/mL, respectively) and the accumulation of SA (5.1 times higher than the control at a concentration of 500 μg/mL). These results suggest that citral activates SAR through the SA pathway. The control efficacies induced by citral (500 μg/mL) on Erysiphe cucurbitacearum, Botrytis cinerea, and Sclerotinia sclerotiorum reached 67.39%, 59.61%, and 63.81%, respectively, indicating that citral can induce plant resistance against fungal diseases. The induced plant disease resistance activity of citral is prominent, with a long duration and a broad spectrum, performing better than the commercial agent chitosan oligosaccharide. Citral thus has the potential to be developed into a new botanical-derived anti-virus agent and plant immunity activator.