Tetrahydrogeranyl quaternary phosphonium salt compound as well as preparation method and application thereof

Abstract

The invention relates to a tetrahydrogeranyl quaternary phosphonium salt compound as well as a preparation method and application thereof in preventing and treating plant diseases, and belongs to the technical field of agricultural chemistry. According to the preparation method, tetrahydrogeranyl halide and a corresponding phosphine reagent are subjected to a reflux reaction in an organic solvent, the yield is high, and the process is simple. The compound, especially the tetrahydrogeranyl triphenyl phosphonium salt, has excellent inhibitory activity on a variety of plant pathogenic fungi such as rhizoctonia solani, decumbent pine mushroom and phytophthora parasitica var nicotianae, IC50 of tetrahydrogeranyl triphenyl phosphonium chloride on decumbent pine mushroom is as low as 0.95 mg / L, and the effect of tetrahydrogeranyl triphenyl phosphonium chloride is remarkably superior to that of a control pesticide chlorothalonil. The invention provides a novel candidate compound for developing a novel agricultural bactericide which is efficient and low in toxicity and is derived from natural products.

Description

Technical Field

[0001] This invention relates to the field of agricultural chemistry, specifically to a new type of quaternary phosphonium salt compound, its preparation method, and the application of this type of compound as an agricultural fungicide in the control of plant pathogenic fungi. Background Technology

[0002] Plant diseases are a major factor restricting agricultural production. The long-term use of chemically synthesized pesticides has led to increasingly serious problems such as environmental pollution, pathogen resistance, and pesticide residues. Therefore, developing novel, highly efficient, low-toxicity, and environmentally friendly fungicides has become a current research hotspot.

[0003] Research on quaternary ammonium salt antibacterial agents is relatively mature, but their long-term use also faces problems such as increased drug resistance. Quaternary phosphonium salts are a class of compounds with similar structures to quaternary ammonium salts but with phosphorus atoms as the positive charge center. Because the radius of phosphorus atoms is larger than that of nitrogen atoms, their polarization ability is stronger, making them more likely to bind to the negatively charged bacterial cell membranes, thus exhibiting higher and broader-spectrum antibacterial activity. They also have potential advantages such as low toxicity and low dosage, making them a promising new type of antibacterial agent.

[0004] Citral is a natural monoterpene aldehyde widely found in the essential oils of plants such as Litsea cubeba, possessing various biological activities including antibacterial and antioxidant properties. However, the aldehyde and alkene bonds in its structure lead to poor chemical stability and high volatility, limiting its direct application. Structural modification of citral to develop stable and efficient derivatives is an important way to enhance its application value.

[0005] Currently, there are no reports on the construction of novel quaternary phosphonium salts using tetrahydrogerany (a hydrogenated derivative of citral) as a hydrophobic chain, combined with triphenylphosphine or tri-n-butylphosphine, and on the systematic study of their antibacterial activity against various plant pathogenic fungi. Summary of the Invention

[0006] In view of this, the present invention aims to provide a series of novel tetrahydrogeranyl quaternary phosphonium salt compounds.

[0007] Another object of the present invention is to provide a simple and efficient method for preparing the above-mentioned compounds.

[0008] Another objective of this invention is to provide the application of the above-mentioned compounds in the prevention and control of plant diseases, especially plant diseases caused by fungi, and to provide candidate compounds for the development of novel plant-derived fungicides.

[0009] This invention is achieved through the following technical solution: A tetrahydrogeranyl quaternary phosphonium salt compound has the structure shown in the following general formula: General formula one: Formula 2: In the formula, X is any one of Cl, Br, and I.

[0010] Further specified, the compound is selected from any one of the following: tetrahydrogeranyltriphenylphosphonium chloride, tetrahydrogeranyltriphenylphosphonium bromide, tetrahydrogeranyltriphenylphosphonium iodide, tetrahydrogeranyltri-n-butylphosphonium chloride, tetrahydrogeranyltri-n-butylphosphonium bromide, and tetrahydrogeranyltri-n-butylphosphonium iodide.

[0011] The method for obtaining the above-mentioned tetrahydrogeranyl quaternary phosphonium salt compound includes the following steps: The tetrahydrogeranyl halide and the phosphine reagent were subjected to a nucleophilic substitution reaction in an organic solvent under reflux conditions. After the reaction was completed, the quaternary phosphonium salt compound was obtained by post-treatment. The phosphine reagent is triphenylphosphine or tri-n-butylphosphine; the halogen in the tetrahydrogeranyl halide reacts with the phosphorus atom in the phosphine reagent.

[0012] Further specified, the molar ratio of the tetrahydrogeranyl halide to the phosphine reagent is 1:(1.0-1.2). The organic solvent is ethyl acetate; The reaction temperature is the reflux temperature of the organic solvent, and the reaction time is 20-30 hours.

[0013] The application of the above-mentioned tetrahydrogeranyl quaternary phosphonium salt compound in the preparation of fungicides for controlling plant pathogenic fungi, wherein the plant pathogenic fungi are selected from at least one of the following: rice sheath blight fungus, pine shoot blight fungus, cottony mildew fungus, tobacco black shank fungus, and watermelon wilt fungus.

[0014] The tetrahydrogeranyl quaternary phosphonium salt compound is tetrahydrogeranyl triphenylphosphonium chloride, tetrahydrogeranyl triphenylphosphonium bromide, or tetrahydrogeranyl triphenylphosphonium iodide.

[0015] An agricultural bactericidal composition comprising a bactericidally effective amount of the aforementioned tetrahydrogeranyl quaternary phosphonium salt compound, and an agronomically acceptable carrier and / or adjuvant.

[0016] The formulation of the agricultural bactericide composition is a wettable powder, a water-dispersible granule, an emulsifiable concentrate, or an aqueous solution.

[0017] The above-mentioned tetrahydrogeranyl triphenylphosphonium chloride was used in the control of *Fotomyces albuminosus* or *Tobacco black shank*, with an IC50 concentration of [missing value]. 50 Less than 10 mg / L.

[0018] The beneficial effects of this invention are as follows: The compounds are novel and exhibit excellent activity: This invention is the first to design and synthesize novel quaternary phosphonium salts with tetrahydrogerany as the hydrophobic chain. These compounds, especially the triphenylphosphine salt series, show significantly higher inhibitory activity against a variety of plant pathogenic fungi than the control pesticide chlorothalonil, demonstrating high efficiency and broad spectrum.

[0019] The raw materials are green and the method is simple: natural citral derivatives are used as starting materials, and the source is renewable. The synthesis method is completed in one step, under mild conditions, simple to operate, and has a high yield (all above 70%), making it suitable for large-scale preparation.

[0020] Clear application prospects: Demonstrates clear antibacterial activity and low IC50. 50 The value indicates that this type of compound has great potential in being developed into a novel agricultural fungicide, providing new ideas and material basis for the creation of plant-derived pesticides.

[0021] Other advantages, objectives, and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination, or may be learned from practice of the invention. The objectives and other advantages of the invention can be realized and obtained through the following description. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the synthetic route for the tetrahydrogeranyl quaternary phosphonium salt compound of the present invention. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0024] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0025] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0026] In the above description of the present invention, it should be noted that the terms "one side," "the other side," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the product of the invention is conventionally placed during use. These terms are used only for the convenience of describing the present invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the present invention. Furthermore, the terms "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0027] Furthermore, terms such as "identical" do not imply that components must be absolutely identical; minor differences are permissible. The term "perpendicular" simply means that the positional relationship between components is more perpendicular than "parallel," not that the structure must be perfectly perpendicular; a slight tilt is acceptable.

[0028] The synthetic route of the tetrahydrogeranyl quaternary phosphonium salt compound of this invention is as follows: Figure 1 As shown, the specific synthesis method is as follows: Add 0.01 mol tetrahydrogeranyl halide (1), 0.01 mol triphenylphosphine (2) or 0.01 mol tributylphosphine (3), and 50 mL ethyl acetate to a 100 mL conical flask. Place a small magnetic stir bar, install a reflux condenser, and place the flask on a magnetic stirrer. Heat and stir under reflux for 24 hours. Take a sample for GC analysis. If the analysis results show that both reactants are present, the reaction is incomplete. Continue the reaction for a period of time depending on the remaining amount. When the analysis results show that one of the reactants is not present, the reaction is complete. Stop heating and stirring, and cool the reaction solution.

[0029] The reaction solution was first rotary evaporated to recover the solvent ethyl acetate. The remaining liquid was washed with petroleum ether (about 10 mL each time) several times until GC analysis showed that there was no raw material in the washing liquid. The product was then transferred to a 10 mL ground glass round-bottom flask for vacuum drying to obtain quaternary phosphonium salt products (4a-4c and 5a-5c). The products were weighed and the yield was calculated.

[0030] Product structure analysis Tetrahydrogeranyltriphenylphosphonium chloride (4a) Molecular formula C 28 H 36 PCl, pale yellow solid, 3.29 g, yield 75%, mp 80.9–81.2 °C.

[0031] ¹H NMR (400MHz, DMSO-d⁶), δ H (ppm): 7.689~7.596(m,15H,3C6H5), 3.308(m,2H, 1-CH2), 1.597(m,1H, 3-CH), 1.464(m,1H, 7- CH), 1.295(m,2H, 2- CH2), 1.139(m, 1H, 4- CH), 1.029(m, 1H, 4- CH), 0.931(m,4H, 5- CH2, 6- CH2), 0.822(d, J = 7.2 Hz, 3H, 9- CH3), 0.648 (d, J = 5.4 Hz, 6H, 8- CH3, 10- CH3); 13 C NMR(100MHz,DMSO-d6), δc(ppm): 135.33(3C -δ ), 133.62 (3C) -γ ), 133.56 (3C) -γ' ), 130.74 (3C) -β ), 130.66 (3C) -β' ), 117.90 (3C) -α ), 44.73(C -1 ),38.94(C -2 ), 36.40(C -6 ), 33.55(C -3 ), 29.22(C -4 ), 27.83(C -7 ), 24.44(C -5 ), 22.63(C -8 C -10 ), 19.27(C -9 ); IR(KBr), ν max (cm -1 ):3051, 2953, 2927, 2889, 2866, 1586, 1463,1436, 1383, 1364, 1112, 995, 740, 690, 540, 508. Tetrahydrogeranyltriphenylphosphonium bromide (4b) Molecular formula C 28 H 36 PBr, light brown solid, 3.77 g, yield 78%, mp 81.8–82.5 °C.

[0032] 1H NMR (400MHz, DMSO-d6), δ H(ppm): 7.933~7.755(m,15H,3C6H5), 3.633(m,2H, 1- CH2), 1.592~1.199 (m, 6H, 2- CH2, 3- CH, 4- CH2, 7- CH), 1.012(m,4H, 5- CH2, 6- CH2), 0.914(d, J = 6.4 Hz, 3H, 9- CH3), 0.818(d, J = 6.8 Hz, 6H, 8- CH3, 10- CH3); 13 C NMR(100MHz, DMSO-d6), δc(ppm): 135.34(3C -δ ), 134.17(3C -β ), 134.07 (3C) -β' ), 130.74 (3C) -γ ), 130.62 (3C) -γ' ),119.54(3C -α ), 50.47(C -1 ), 38.95(C -2 ), 35.98(C -6 ), 33.71(C -3 ), 28.83(C -4 ), 27.83(C -7 ), 24.48(C -5 ), 23.03, 22.92(C -8 C -10 ), 19.40(C -9 ); IR(KBr), ν max (cm -1 ):3056,2954, 2926, 2868, 2799, 1587, 1551, 1476, 1436, 1383, 1366, 1115, 996, 742,693, 541, 511. Tetrahydrogeranyltriphenylphosphonium iodide (4c) Molecular formula C 28 H 36 PI white solid, 4.35 g, yield 82%, mp 83.1~83.6℃.

[0033] 1H NMR (400MHz, DMSO-d6), δ H (ppm): 7.846~7.759(m,15H,3C6H5), 3.563(m,2H, 1- CH2), 1.728(m, 1H, 3- CH), 1.627(m, 1H, 7- CH), 1.467(m,2H, 2- CH2), 1.308~1.119(m,6H, 4- CH, 5- CH2, 6- CH2), 0.990(d, J = 6.4 Hz, 3H, 9- CH3), 0.821(d, J = 6.8 Hz, 6H, 8- CH3, 10- CH3); 13 C NMR(100MHz, DMSO-d6), δc(ppm): 135.11(3C -δ ), 130.47 (3C) -γ ), 133.37(3C -γ' ), 130.41(3C -β 3C -β' ), 118.43 (3C) -α ), 44.56(C -1 ), 38.85(C -2 ), 36.31(C -6 ),33.56(C -3 ), 29.12(C -4 ), 27.73(C -7 ), 24.35(C -5 ), 22.54, 22.38(C -8 C -10 ), 19.20(C -9 ); IR(KBr), ν max (cm -1 ):3050, 2951, 2928, 2887, 2863, 1585, 1436, 1383,1365, 1112, 994, 743, 689, 538, 506. Tetrahydrogeranyl-tributylphosphonium chloride (5a) Molecular formula C 22 H 48 PCl is a light brown, viscous liquid, 2.73 g, yield 72%.

[0034] 1H NMR (400MHz, DMSO-d6), δ H (ppm): 2.262 (m, 8H, 1- CH2,3 α- CH2), 1.5~1.2 (m, 18H, 2- CH2, 3- CH, 7- CH, 6- CH2, 3β- CH2, 3γ- CH2), 1.150(m,4H, 4- CH2, 5- CH2), 0.927~0.834 (m, 18H, 8- CH3, 9- CH3, 10- CH3,3 δ- CH3); 13 C NMR(100MHz,DMSO-d6), δc(ppm): 39.13(3C -α ),36.10(C -1 ), 33.73, 33.59(C -3 ), 27.89(C -7 ), 27.60(C -2 ), 24.54(C -6 ), 23.91, 23.75 (3C) -β ), 23.16(C -4 ), 22.99(C -8 ), 22.91(C -10 ), 19.26(C -9 ), 18.05, 17.58 (3C) -γ ),16.02(C -5 ), 13.71(3C -δ ); IR(KBr), ν max (cm -1 ): 2956, 2930, 2871, 1461, 1382,1365, 1232, 796. Tetrahydrogeranyl-tributylphosphonium bromide (5b) Molecular formula C 22 H 48 PBr is a light brown, viscous liquid, 3.17 g, yield 75%.

[0035] 1H NMR (400MHz, DMSO-d6), δ H(ppm): 2.262 (m, 8H, 1- CH2,3 α- CH2), 1.522~1.383 (m, 18H, 2- CH2, 3- CH, 7- CH, 6- CH2,3 β- CH2,3 γ- CH2), 1.299(m,2H, 4- CH2), 1.149(m,2H, 5- CH2), 0.937~0.853 (m, 18H, 8- CH3, 9- CH3, 10- CH3,3 δ- CH3); 13 C NMR(100MHz,DMSO-d6), δc(ppm):39.13(3C -α ), 36.09(C -1 ), 33.72, 33.58(C -3 ), 27.89(C -7 ), 27.60(C -2 ), 24.54(C -6 ), 23.90, 23.74 (3C) -β ), 23.22(C -4 ), 23.01(C -8 ), 22.90(C -10 ), 19.29(C -9 ), 18.10, 17.63 (3C) -γ ), 16.07(C -5 ), 13.73 (3C) -δ ); IR(KBr), ν max (cm -1 ): 2956, 2929, 2871, 1462,1383, 1364, 1232, 794. Tetrahydrogeranyl-tributylphosphonium iodide (5c) Molecular formula C 22 H 48 PI was a nearly white semi-solid substance, 4.45 g, with a yield of 78%.

[0036] 1H NMR (400MHz, DMSO-d6), δ H (ppm): 2.239(m,8H, 1- CH2,3α- CH2), 1.539~1.385 (m, 18H, 2- CH2, 3- CH, 7- CH, 6- CH2,3 β- CH2,3 γ- CH2), 1.299(m,2H, 4- CH2), 1.149(m,2H, 5- CH2), 0.938~0.852 (m, 18H, 8- CH3, 9- CH3, 10- CH3,3 δ- CH3); 13 C NMR(100MHz,DMSO-d6), δc(ppm):39.12(3C -α ), 36.07(C -1 ), 33.70, 33.56(C -3 ), 27.89(C -7 ), 27.58(C -2 ), 24.53(C -6 ), 23.88, 23.73 (3C) -β ), 23.21(C -4 ), 23.03(C -8 ), 22.92(C -10 ), 19.31(C -9 ), 18.12, 17.64 (3C) -γ ), 16.09(C -5 ), 13.75 (3C) -δ ); IR(KBr), ν max (cm -1 ): 2956, 2928, 2871, 1461,1382, 1364, 1231, 794. Antibacterial activity test The inhibition rates of six tetrahydrogeranyl quaternary phosphonium salts and chlorothalonil against eight plant pathogens were determined using the mycelial growth rate method. Concentration gradients were set up according to the experiment. After weighing the calculated compounds, dimethyl sulfoxide (DMSO) was used as the solvent to dilute the compounds sequentially to 200, 100, 50, 25, 12.5, and 6.25 mg / L solutions. These solutions were added to potato dextrose agar (PDA) medium, with three replicates for each concentration. PDA with an equal volume of DMSO was used as a control. All inoculum strains were inoculated sequentially, labeled, sealed with sealing film, and incubated at 25°C. When the mycelial diameter of the control group reached 6–7 cm, the colony diameter was measured using the cross-crossing method. The inhibition rate was calculated based on the colony diameter using the following formula: Colony diameter (cm) = Actual colony growth diameter (cm) - Mycelial cake diameter (0.5 cm) Finally, based on the mycelial growth inhibition rate, a virulence regression equation y=a+bx was established using statistical analysis software (IBM SPSS Statistics 25) (the logarithm of the drug concentration is the X-axis, and the probability of the inhibition rate conversion is the Y-axis). When y=50%, the half-inhibition concentration (IC50) can be calculated. 50 This refers to the concentration required to achieve a 50% inhibition effect.

[0037] Antibacterial activity analysis The six synthesized tetrahydrogeranyl quaternary phosphonium salts were prepared into solutions with mass concentrations of 200, 100, 50, 25, 12.5, and 6.25 mg / L, respectively. Activity tests were conducted on eight plant pathogens. Taking a solution concentration of 50 mg / L as an example, the antibacterial activity is shown in Table 1. Table 1. Inhibition rate (%) of tetrahydrogeranyl quaternary phosphonium salts against eight plant pathogens. *The drug concentration is 50 mg / L, where R represents tetrahydrogeranylide. K: Rice sheath blight pathogen; S: Pine shoot blight pathogen; X: Watermelon wilt pathogen; H: Cotyledon rotundifolia; O: Fusarium verticillata; V: Leymus chinensis; 11: Tobacco black shank pathogen; Cf: Camellia oleifera fruit-spiny spirocoecaria Table 26 IC50 values ​​of quaternary phosphonium compounds against 8 plant pathogens. 50 Value (mg / L) The antibacterial data listed in Table 1 show that the antibacterial activity of tetrahydrogeranyl triphenylphosphonium halide (4a, 4b, 4c) against eight plant pathogens is higher than that of the corresponding tetrahydrogeranyl tri-n-butylphosphonium halide (5a, 5b, 5c). Among them, the inhibition rates of 4a, 4b, and 4c against *Floccospora hygroscopica* (H) and *Bacillus thuringiensis* (11) are all 100%; the inhibition rates against *Rhizoctonia solani* (K) and *Pinus thunbergii* (S) are all above 92.5% (except for 4c, which has an inhibition rate of 89.6% against *Pinus thunbergii*). Moreover, the inhibition rates of these three compounds against five pathogens (K, S, H, 11, and X, *Fusarium wilt*) are significantly higher than those of the pesticide chlorothalonil. The inhibition rates of 5a, 5b, and 5c against *Potentilla chinensis* were all higher than 97.8%; the inhibition rates against S, X, H, and 11 (except for 5c, which had an inhibition rate of 61.4% against *Tobacco Black Shank*) were all higher than those of the pesticide chlorothalonil.

[0038] The data in Table 1 also shows that: the cations are the same, while the anions (Cl...) - ,Br - I - The antibacterial rates of different quaternary phosphonium salts (e.g., 4a, 4b, 4c against K, X, H, O, 11; 5a, 5b, 5c against K, S, H, V, Cf) were not significantly different, but other antibacterial activities indicated that anions had an impact on the antibacterial rate.

[0039] The IC50 values ​​of the six quaternary phosphonium compounds listed in Table 2 against eight plant pathogens are... 50 The values ​​show that the antibacterial activity of tetrahydrogeranyltriphenylphosphonium halide (4a, 4b, 4c) against eight plant pathogens was higher than that of the corresponding tetrahydrogeranyltri-n-butylphosphonium halide (5a, 5b, 5c). The IC50 values ​​of the six compounds against H were also shown. 50 The values ​​were all below 20 mg / L, with 4a and 4c having values ​​of 0.95 mg / L and 2.00 mg / L, respectively, lower than the pesticide chlorothalonil's 5.31 mg / L. The IC50 values ​​of all five compounds (except 5c) against compound 11 were also below 20 mg / L, with 4a, 4b, and 4c having IC50 values ​​below 20 mg / L. 50 The values ​​were all lower than the pesticide chlorothalonil's 5.34 mg / L; the IC50 values ​​of the six compounds against X were... 50 The values ​​were all far lower than the IC50 of the pesticide chlorothalonil. 50 =685.6 mg / L, of which 4a, 4b, and 4c were below 20 mg / L, with the lowest being 4.99 mg / L for 4b; IC50 values ​​of the four compounds (except 5b and 5c) against K and 4a, 4b, and 4c against S. 50 The values ​​were all below 20 mg / L, indicating good antibacterial activity.

[0040] in conclusion Six tetrahydrogerany quaternary phosphonium salts (4a-4c, 5a-5c) were synthesized by reacting tetrahydrogerany halides (chlorine, bromine, and iodine) with triphenylphosphine and tri-n-butylphosphine, respectively. Their structures were confirmed by IR, 1H NMR, and 13C NMR.

[0041] The mycelial growth rate method was used to test the antibacterial activity against eight plant pathogens. The results showed that six quaternary phosphonium salt compounds exhibited certain antibacterial activity against the tested pathogens. At a concentration of 50 mg / L, compounds Ph3PRCl, Ph3PRBr, and Ph3PRI showed inhibition rates exceeding 80% against K, S, X, H, and I1, surpassing the inhibition rate of the pesticide chlorothalonil at the corresponding concentrations. In particular, the inhibition rates against H and I1 reached 100%. Compounds n-Bu3PRCl, n-Bu3PRBr, and n-Bu3PRI also showed good antibacterial activity against S, X, H, and I1, with most exceeding the inhibition rate of chlorothalonil. The inhibition rate against H exceeded 97.8%.

[0042] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A tetrahydrogeranyl quaternary phosphonium salt compound, characterized in that, It has the structure shown in the following general formula: General formula one: Formula 2: In the formula, X is any one of Cl, Br, and I.

2. The tetrahydrogeranyl quaternary phosphonium salt compound according to claim 1, characterized in that, The compound is selected from any one of the following: tetrahydrogeranyltriphenylphosphonium chloride, tetrahydrogeranyltriphenylphosphonium bromide, tetrahydrogeranyltriphenylphosphonium iodide, tetrahydrogeranyltri-n-butylphosphonium chloride, tetrahydrogeranyltri-n-butylphosphonium bromide, and tetrahydrogeranyltri-n-butylphosphonium iodide.

3. A method for preparing the tetrahydrogeranyl quaternary phosphonium salt compound as described in claim 1 or 2, characterized in that, Includes the following steps: The tetrahydrogeranyl halide and the phosphine reagent were subjected to a nucleophilic substitution reaction in an organic solvent under reflux conditions. After the reaction was completed, the quaternary phosphonium salt compound was obtained by post-treatment. The phosphine reagent is triphenylphosphine or tri-n-butylphosphine; the halogen in the tetrahydrogeranyl halide reacts with the phosphorus atom in the phosphine reagent.

4. The method according to claim 3, characterized in that: The molar ratio of the tetrahydrogeranyl halide to the phosphine reagent is 1:(1.0-1.2). The organic solvent is ethyl acetate; The reaction temperature is the reflux temperature of the organic solvent, and the reaction time is 20-30 hours.

5. The use of a tetrahydrogeranyl quaternary phosphonium salt compound as described in claim 1 or 2 in the preparation of a fungicide for controlling plant pathogenic fungi.

6. The application according to claim 5, characterized in that, The plant pathogenic fungi are selected from at least one of the following: rice sheath blight fungus, pine shoot blight fungus, cottony mildew fungus, tobacco black shank fungus, and watermelon wilt fungus.

7. The application according to claim 5, characterized in that, The tetrahydrogeranyl quaternary phosphonium salt compound is tetrahydrogeranyl triphenylphosphonium chloride, tetrahydrogeranyl triphenylphosphonium bromide, or tetrahydrogeranyl triphenylphosphonium iodide.

8. An agricultural bactericidal composition, characterized in that, It contains a bactericidal effective amount of the tetrahydrogeranyl quaternary phosphonium salt compound as described in claim 1 or 2, and an agronomically acceptable carrier and / or adjuvant.

9. The agricultural bactericidal composition according to claim 8, characterized in that, The formulation of the agricultural bactericide composition is a wettable powder, water-dispersible granule, emulsifiable concentrate, or aqueous solution.

10. The application according to claim 5 or 7, characterized in that, The application of the tetrahydrogeranyl triphenylphosphonium chloride in the control of *Fomitopsis pinnatifida* or *Tobacco black shank* fungus, with an IC50 concentration of [missing value]... 50 Less than 10 mg / L.

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