Background Art Agricultural and horticultural plant diseases inflicted by bacterial and fungal pathogens cause an enormous loss of agricultural and horticultural crops worldwide, with devastating effects including millions of dollars'damage each year, especially to fruit crops.

Bacterial and fungal pathogens destroy plants worldwide, including species of Rutaceae, such as Citrus spp, Fortunella spp, and Poncirus spp, which produce citrus such as oranges, sour oranges, grapefruit, tangerines, lemons, and limes; cereal crops are also affected. These pathogens thus adversely affect an essential worldwide food supply line. The State of Florida alone relies on an $8. 5 billion citrus industry to sustain its economy.

Considered the most important bacterial plant disease- causing agent worldwide, citrus canker is a highly- contagious agent which is transmitted easily by infected nursery stock, budwood, leaves, twigs and fruit, and even by non-botanical carriers such as wind-driven rain, insects, animals, people, and contaminated equipment. The most conspicuous symptoms occur on fruit and leaves, where lesions appear as small, round, blister-like eruptions having initially a whitish color but turning to an unsightly tan or brown. Progression of the lesions is indicated by a water-soaked oily area that develops around the lesion.

While infection is usually confined to the fruit, more pronounced lesions can form crater-type depressions on the twigs. Quarantine is generally imposed until the disease is

eradicated or until sufficient evidence is accumulated that the disease shall not contaminate other areas.

The relevant disease-causing agents applicable to this invention are found in Florida, Mexico, several countries in South America, Japan, South Africa, and countries in Asia.

However, introduction into other countries remains a distinct possibility.

Objects of the Invention and Industrial Applicability It is a general object of the present invention to provide compounds, compositions, and methods of use thereof, for the treatment and prevention of bacterial and fungal plant diseases.

It is an object of the present invention to provide compounds, compositions, and methods of use thereof, for the treatment and prevention of bacterial and fungal plant diseases in a wide variety of species of agricultural and horticultural plants.

It is a further object of the present invention to provide compounds, compositions, and methods of use thereof, for the treatment and prevention of bacterial and fungal plant diseases which are of low cost, exhibit ease of applicability, and demonstrate low toxicity to plants and consumers of plants while providing high success rates of such treatment and prevention.

Summary of the Invention The present invention relates to compounds, compositions, and their use in the treatment and prevention of bacterial and fungal infections in plants. Accordingly, because of the strong antimicrobial and antifungal action and the good stability of such compounds, the present invention has high practical utility both as a treatment and preventive remedy against bacterial and fungal plant infections.

More particularly, the present invention involves applying to susceptible plant varieties one or more compounds having the following formula:

wherein R'and R"are each independently a straight or branched chain alkyl moiety of 5 to 8 carbon atoms; M is NH4+, Na+, K, or Ca+2 ; and x is 1 when M is NH4+, Na+, or Ks and x is 2 when M is Ca. The compounds are effective for treating bacteria and fungal infections in agricultural and horticultural plants and may be applied alone or in combination with a suitable diluent or carrier. The carrier may be one adapted to facilitate systemic administration of the aforementioned compound, either by facilitating uptake of the compound by the roots of the plant or by facilitating passage of the compound across a stem or leaf surface of a plant. In vascular plants, systemic administration will preferably permit the compound to enter phloem or xylem tissue of the plant.

Suitable carriers or diluents are known in the art, including water, alcohols, solutions in water-miscible organic solvents, and vegetable oils. Because carriers or diluents which minimize or prevent the compound from being washed from the surface of a plant leaf or stem or from soil particles enhance the rainfastness of the formulation, such solutions are preferred.

Best Mode for Carrying Out the Invention The compounds of the present invention are compounds of the formula: wherein R'and R"are each independently a straight or branched chain alkyl moiety of 5 to 8 carbon atoms; M is NH4+, Na+, K+, or Ca+2 ; and x is 1 when M is NH4+, Na+, or K+ and x is 2 when M is Ca+2. The M ion and the amount of the compound are each selected such that the amount of M applied to a particular plant will be in a non-toxic range. The R' and R"groups may be the same or different. Preferably, R' and R"are amyl, octyl, or 2-ethylhexyl; more preferably, R' and R"are each 2-ethylhexyl. Preferably, M is Na'or Ca and most preferably, M is Na+.

While the compounds of the present invention are used or formulated for use alone, they may also be combined with a antimicrobial agent and/or a pesticide. Thus, the present invention comprises applying compounds of the above formula in the presence or absence of conventional antimicrobial compounds such as organic copper, inorganic copper, and antibiotics such as blasticidis S, kasugamycin, validamycin, novobiocin, oxytetracycline, and cycloheximide. Omitting such compounds reduces introduction of toxic metallic compounds into the environment and may minimize the emergence of antibiotic-resistant strains of pathogenic organisms. The compounds of this invention also function as surfactants/wetting agents and may eliminate the use of other such agents or may improve formulation with siloxane or surfactants intended to enhance rainfastness.

A preferred compound according to the present invention is a docusate salt such as docusate sodium, which is known in the prior art as both a food additive and as a laxative suitable for ingestion by humans and mammals. The latter

salt is a waxlike solid that is very soluble in water- miscible organic solvents and is also soluble in water. The water solubility of docusate sodium is equal to 71,000 mg/L at 25°C. 1000ppm aqueous solutions of docusate salt for irrigation of plants may be prepared by first preparing an 0.8% solution of the compound in water followed by a further 1: 8 dilution with water. Docusate sodium can be prepared by esterification of maleic anhydride with 2-ethylhexyl alcohol followed by the addition of sodium bisulfite. The other compounds of the present invention can be prepared by esterification of maleic anhydride with the appropriate acceptable alcohol followed by the addition of the appropriate bisulfite salt, such as potassium bisulfate, ammonium bisulfate, and calcium bisulfite.

The compounds and formulations thereof are effective in treating and preventing a variety of plant diseases caused by bacteria, fungi, and viruses. These compounds and formulations also display better antimicrobial action for the treatment and prevention of plant disease than the products known from the state of the art. For example, control practices for citrus canker other than quarantine or burning of the infected citrus groves are expensive, ineffective, and present the potential of environmental contamination. However, docusate sodium has proved lethal to the causative agent of citrus canker, Xanthamonas campestris pv. Citri, and to the related organism Xanthamonas axonopodis pv. Citri.

Compounds of the present invention, and formulations thereof, may be applied on leaves or stems and/or soil of infected and susceptible but uninfected plants, or onto the water surface, into water, to the soil surface, or into the interior of the soil. One preferred method is spray application to aboveground portions (stems and leaves) of the plants. Other application methods include watering the plant or soil, or atomizing, misting, or vaporizing the compound. The active ingredient concentration should be present in effective amounts; this concentration depends on the particular antimicrobial used and the desired response.

Preferred concentrations of the compound in antimicrobial formulations of this invention is about 0.1- 50% by weight. However, the concentration may be suitably varied according to the intended use of the antimicrobial.

In practicing the method of this invention, the application rate of the compound will depend on the kind of disease, the degree of onset of the disease, the kind of plant to be treated, the location of the application, the method of application to be used, and the specific compound or formulation used.

The present invention includes methods for preventing and treating the action of plant disease-causing agents including, but not limited to, Aspergillus flavus, the fungal causative agent that induces crop mycotoxins or lethal aflatoxins; Xanthamonas campestris, the causative agent of citrus canker; and Agrobacterium tumefaciens, the causative agent of crown gall disease. Other diseases that may be treated include bacterial leaf plight of rice; bacterial shot hole of peach; black rot of cabbage; bacterial blight of lettuce; bacterial spot of melon; leaf blight of soy bean; and tomato canker. The present invention provides a generally safe and effective method for the treatment and prevention of agricultural and horticultural plant diseases with minimal detriment to the environment. For example, as previously mentioned, docusate sodium is widely used as both a food additive and as a laxative for human and mammal consumption.

Collectively in the appended claims and herein, the term"antimicrobial"relates to activity against plant pathogens, including plant disease-causing bacteria and plant disease-causing fungi, both of which may be termed "plant disease-causing agents"or"agents."The term "plant"includes vascular plants.

Example 1 Treatment and prevention of agricultural and horticultural plant disease by using docusate sodium Xanthamonas campestris pv. Citri pathogen (Xcc) was obtained from 24-hour old slant cultures on nutrient agar incubated at 28°C. Bacterial cells were suspended in sterile tap water, and inoculum concentration was standardized at 106 cells/mL by adding 2mL of a 108 cells/mL suspension (108 cells/mL = 0. 3 absorbance at 600nm on spectronic 20) to 198mL of sterile tap water. A stock solution of 8000ppm docusate sodium (DS) was prepared by dissolving 80mg of DS in lOmL of sterile tap water. A series of ten 18 x 150mm test tubes containing 2mL each of full-strength sterile DIFCO nutrient broth (NB) was used in a double dilution format to test the antimicrobial effectiveness of DS. In tube no. 1, 2mL of 8000ppm DS in sterile tap water was added to the 2mL of NB, mixed thoroughly, then 2mL extracted and transferred aseptically to tube no. 2, mixed thoroughly, then 2mL was extracted and transferred aseptically to tube no. 3, etc., until tube no.

9 received 2mL, was mixed thoroughly, then 2mL extracted and discarded. Tube no. 10 served as a control with no added DS. This procedure resulted in a series of ten tubes containing 2mL each, with tube no. 1 = 2000ppm DS (2000ppm DS if original DS solution is 8000ppm), tube no. 2 = 1000ppm, tube no. 3 = 500ppm, etc., tube no. 9 = 18ppm, and tube no. 10 = Oppm DS. At this point, 2mL of 106 cells/mL of Xcc were added aseptically to each tube and exposed to the now-halved DS concentration for 48 hours. Thus, standardized populations of bacteria were exposed to a graduated series of measured DS concentrations for 48 hours.

After 48 hours'exposure of bacteria to DS, growth was recorded and 0.05mL of the solution in each tube was transferred to the surface of the DIFCOTM nutrient agar to check in minimum inhibitory and minimum lethal concentrations were the same. The 0.05mL volume was transferred aseptically using a micro-diluter (capillary

transfer pipette), and the transferred volume was spread evenly over the agar surface using a flamed, bent glass rod.

Test plates were inoculated at 28°C for 48 hours, at which time presence or absence of bacterial growth was recorded (see Table 1, test 1). DS at 1000ppm proved lethal to a 5 x 105 cells/mL Xcc in 48 hours. Transfers after 48 hours demonstrated that minimum inhibitory concentration was the same as the minimum lethal concentration.

Similar results were obtained by the treatment of Xanthamonas axonopodis pv. Citri with DS (see Table 1, test 2).

Table 1 Test 1: Tube no. 1 = 2000ppm DS, 48 hr exposure Tube no. 1 2 3 4 5 6 7 8 9 10 Growth--+ + + + + + + + Minimum inhibitory concentration = 1000ppm Minimum inhibitory concentration = 1000ppm Test 2: Tube no. 1 = 2000ppm DS, 48 hr exposure Tube no. 1 2 3 4 5 6 7 8 9 10 Growth--+ + + + + + + + Minimum inhibitory concentration = 1000ppm Minimum inhibitory concentration = 1000ppm While the present invention has been described in connection with exemplary embodiments thereof, it will be understood that many modifications in both design and use will be apparent to those of ordinary skill in the art; and this application is intended to cover any adaptations or variations thereof. Therefore, it is manifestly intended that this invention be limited only by the claims and the equivalents thereof.