MXPA99007288A - Method for treating cotyledonous plants - Google Patents

Abstract

Application of an aqueous solution containing a chitosan salt and oligomers of chitosan to the foliage of growing plants increases the yield of vegetables, tubers, cereal grains, fruits, and blossoms.

Description

METHOD FOR THE TREATMENT OF COTILEDON PLANTS FIELD OF THE INVENTION The invention is directed to a method for the treatment of cotyledonous plants to improve the yield, health and vigor of the plant by spraying an aqueous solution containing oligomers of chitosan and a salt of chitosan on the leaves of the plant. .

BACKGROUND OF THE INVENTION Chitosan is a naturally occurring polymer found in many fungi. It can be broadly described as a copolymer of D-glucosamine and N-acetyl-D-gru "cosamine in which 65-100., Of the monomer units are D-glucosamine, since it is a member of the chemical class known as Amines, which are weakly basic, readily and reversibly form salts with acids such as mineral acids and carboxylic acids Many of these salts are soluble in water In a system in which chitosan and an acid are present, both (1) units of glucosamine, electrically neutral and (2) units in which the glucosamine unit is protonated and associated with the anion corresponding to the REF .: 30963 acid will be present in the polymer chain in proportions that are pH dependent. Such a system is commonly referred to as a chitosan salt without considering the degree to which the glucosamine units are protonated. For clarity and brevity, such systems will be referred to later as chitosan salts but it should be understood that such terminology includes species in which free, amino groups may be present. It has been amply demonstrated that the application of chitosan salts to the seeds of cereal plantations results in dramatic changes in the biochemistry of the emerging plant. Such changes include the increased production of a class of compounds known as phytoalexins, which provide protection against localized microbial infection, and diminished production of callose and lignin, which provide structural resistance and a barrier to the spread of infection. These changes occur as a result of the activation of the gene encoding the enzyme phenylalanine ammoni to lyase, which is involved in the step of determining the speed of the phenylpropanoid metabolism pathway. It has been shown that chitosan includes the synthesis of terpenoid phytoalexins which are closely involved in the biosynthesis of growth hormones such as gibberellic acid and abscisic acid. Guitosana includes the activation of genes that produce chitinase and glucanase enzymes that are known to be both fungal inhibitors and play a role in the development of pollen and seed germination. Chitosan also includes the activation of genes that produce protease inhibitors that help protect the plant from insect attack. On a macroscopic scale, these changes translate into increased root development, reduced fall (plants that fall before harvest), increased yield and resistance to certain plant diseases. -US Patent No. 4,812,159 (Freepons) describes in detail the treatment of soil in a zone of planting seeds with a solution of chitosan, the application of a solution of chitosan to plant seeds, the treatment of soil in the area of planting seeds with a mixture of solid chitosan and a solid acid, and the ground treatment in the seed-planting zone with a solid chitosan salt. The preferred chitosan solution was one containing more than 1.5 equivalents of glutamic acid per mole of amino function in chitosan.

The application of chitosan to the foliage of an emergent plant is mentioned, but there is no description of the methods required to perform such treatment, nor of the results achieved with them. For all these Freepons treatments, it is stipulated that when an acidic component is used in making the chitosan preparation, the acid must be selected from the group of non-phytotoxic acids, which are defined as those that do not cause an adverse effect, significant in the germination of the seeds or in the development of the seedlings. U.S. Patent No. 4,964,894 is a continuation in part of U.S. Patent No. 4,812,159 and indicates that glutamic acid, tartaric acid, citric acid, adipic acid, hydrochloric acid, formic acid "and nitric acid meet the criteria of non-phytotoxicity The acetic acid and the butyric acid were found to be phytotoxic and harmful for the development of the seedling of the plant, which would render these acids unsuitable for use according to the Freepons teaching. According to the teachings of U.S. Patent No. 4,812,159, by applying a chitosan preparation to the seeds or by immersing the seed in such preparation, followed by drying.Drying is necessary to prevent premature germination of the seed in the range of time between treatment and sowing In the absence of a drying step, it is recommended that sowing occurs within 60 h oras of the treatment of the seeds. While seed treatment is easily carried out on a small scale using the methods described, treatment protocols can not be extended to commercial scale operations without the invention of specialized equipment or modification of the equipment commonly used in the industry. seed coatings such as grain movement devices similar to the Gustavson seed coater. This is a serious disadvantage in commercial seed coating operations where the same piece of equipment should also be used to apply other treatments (for example, fungicides) to the seeds and can not be used only with chitosan. In addition, the treatment is limited to an individual application of chitosan in the very early stage of plant growth that is not repeated or reinforced in other key stages of plant growth such as flowering, seed formation and maturation.

Treating the soil in the seed-planting zone with a chitosan preparation requires that the preparation be distributed in a region in close proximity to where the seed will be planted. Therefore, specialized equipment is required to carry out the treatment to the region where the seed will eventually germinate. While this can easily be done in the case of mechanized seeding, this technique is not compatible with other methods such as planting from aircraft or broadcast sowing. In addition, the two techniques that use chitosan in the form of a solid require that the solid be introduced in the form of very small particles (0.5-100 μm) which therefore requires elaborating the pre-processing of the chitosan to put it in a suitable form for the application. As with seed treatment, the treatment of the soil in the germination region of the seeds is limited to individual treatment at the very early stage of plant growth so that the root system of the plant is not disrupted. Since no method is described for the application of chitosan to the foliage of emerging plants, it is not known if this technique provides any beneficial effect. Clearly thought, it shares with the other methods the limitation that treatment is restricted to the earliest stage of plant growth. U.S. Patent No. 4,964,894 again describes the same techniques noted above and then goes on to describe a method for identifying non-phytotoxic acids. Glutamic acid, tartaric acid, citric acid, adipic acid, hydrochloric acid, formic acid and nitric acid were found to meet the criteria for non-phytotoxicity. The acetic acid and the butyric acid were found to be phytotoxic and therefore detri intal for the development of the planting. The preferred chitosan solution is one that contains more than 1.5 equivalents of "glutamic acid per mole of amino-function in chitosan." Another technique is described in U.S. Patent No. 5,554,445 (Kivekas, Struszczyk) which involves spraying seeds with a liquid dispersion of microcrystalline chitosan followed by drying to form a polymer film around the seed In order to form an appropriate film on the seed, it is specified that the chitosan must have a water retention value of 200. -5,000%, hydrogen bonding potential of 10-25 kJ / mol, and particle size of 0.1-100 μm As noted, these procedures require specialized equipment, elaborate pre-processing of chitosan and are limited to one treatment individual at the earliest stage of plant growth, US Patent No. 4,886,541 (Hadwiger) describes the application of a chitosan preparation to the wheat seed in order to increase yield, reduce the fall, and increase the development of the root. The treatment is carried out by applying an aqueous solution of chitosan acetate to the seed in such a way that the seed is agitated to distribute the liquid on the seed. The recommended techniques are the use of a grain movement device or a cement mixing equipment. As discussed above, the application of chitosan to the seeds by the teachings of this description adds complexity and cost to the commercial coating of the seeds and is limited to an individual application at the earliest stage of plant growth. U.S. Patent No. 4,978,381 (Hadwiger) and U.S. Patent No. 5,104,437 (Hadwiger) describe the same techniques for seed treatment and provide additional examples for extending the method to other cereal crops such as rice, oats, barley and rye . The American patent application, copending applicant, Serial Number (CV-0084) describes a method for the treatment of plants by foliar application of a solution of chitosan salt that results in increased yield, better resistance to drought, and improved overall vigor. Chitosan salt is prepared from chitosan of molecular weight greater than 50,000 amu (units of atomic mass, daltons) and an acid that forms a salt of water-soluble chitosan in proportions such that the ratio of equivalents of acid to amino groups is 1.02-1.20. Chitosan has been used in agriculture for purposes other than its ability to increase crop yields. It has also shown properties as a bactericide against a variety of microorganisms and has been used where this property can be put to a good advantage. The use of chitosan to inhibit damage by frost is described in Japanese Patent Application No. 07179843 (assigned to Daiiche Seimo KK), wherein the spinach leaves inoculated with the nucleating organisms of the ice, P. syringae and P agglomerans, were treated with chitosan and then exposed to the freezing temperature. The treated leaves had significantly less frost damage than the controls. In addition, the North American patent No. ,374,627 describes the use of a 10,000-50,000 molecular weight chitosan hydrolyzate prepared by acid catalyzed degradation at high temperature of chitosan as an effective agent for the protection of plants against a number of plant diseases such as bacterial, soft decomposition. (vegetables), dead zone in spring (herbs for lawns), and bacterial decomposition of grains (rice).

BRIEF DESCRIPTION OF THE INVENTION The invention is therefore directed to the application of a solution containing both a salt of chitosan and oligomers of guitosana to the foliage of growing plants to increase the yields of vegetables, seeds, fruits, tubers and blooms. Plants treated in this way are healthier, more resistant to drought, and many varieties of plants enjoy a period of extended production. The treatment can be repeated throughout the growth cycle of the plant, especially during the critical stages of plant growth such as flowering, seed formation and maturation. Therefore, the invention is directed primarily to a method for improving the yield, health and vigor of growing cotyledon plants comprising (1) sprinkling on the foliage between the appearance of the first true leaves and the harvest of the plant or the fruit thereof an aqueous solution containing dissolved therein 0.01-1.50% by weight of a water soluble salt of chitosan and an acid, solution in which the ratio of equivalents of acid to amino groups derived from chitosan is 1.02-1.20 and also dissolved in the same 0.1-15.0% oligomers. of chitosan based on the weight of the chitosan salt (exclusive of the anion) and (2) repeating step (1) before harvesting the plant or the useful portion thereof. In a further aspect, the invention is directed to a treatment solution described above. In a still further aspect, the invention is directed to a method for the preparation of the treatment solution described above comprising (1) dispersing chitosan particles in water at 45-85 C and adding thereto an acid forming a soluble salt in water when it is reacted with chitosan, in an amount such that the ratio of equivalents of acid to amino groups derived from chitosan is 1.01-1.20 and (2) adding thereto oligomers of chitosan in an amount such that the oligomers are equal to 0.1-15.0% of the weight of the chitosan (exclusive of the anion).

DEFINITION As used herein, the term "harvest" and various forms thereof refers not only to the harvesting of the useful or edible portion of the growing plants, but also to the harvesting of the entire plant. Examples of the above are collecting fruit from the trees, picking beans from the plants, picking corncobs from the peduncles, chopping cabbage or celery, etc. Examples of the latter are plucking vegetables from roots such as potatoes, beets and carrots.

DETAILED DESCRIPTION OF THE INVENTION A. Chitosan Composition It is believed that chitosan is a naturally occurring polymer found in many fungi, is neither abundant nor easily isolated from natural sources in high purity. As a matter of convenience, chitosan is most easily obtained from chitin which, after cellulose, is the second most abundant natural polymer. Chitin is easily isolated from shellfish shells or insect dermatoskeletons and is also found in molluscs and fungi. It is a water-insoluble copolymer of N-acetyl-D-glucosamine and D-glucosamine, but the higher preponderance of monomer units consists of N-acetyl-D-glucosamine residues. Chitosan is a copolymer of the same two monomer units, but the preponderance of monomer units are D-glucosamine residues. Since the D-glucosamine residues carry a basic amino function, they easily form salts with acids. Many of these salts are soluble in water. "The treatment of chitin with a caustic substance, concentrated at high temperature, converts the N-acetyl-D-glucosamine residues into D-glucosamine residues and converts chitin into chitosan. A convenient method for obtaining the chitosan chitosan found in seafood shell wastes is described in US Patent No. 3,862,122 (Peniston), although there is a continuous medium of possible compositions between poly-N-acetyl-D-glucosamine. Pure and pure poly-D-glucosamine, the term guitosana is generally applied to those polymers containing 65-100% D-glucosamine residues.The compositions within this range are soluble in acidic solutions, but if more than about 35 % of the monomer residues are N-acetyl-D-glucosamine, the polymer is insoluble in weakly acidic solutions, commercially available chitosan is typically prepared from shells of seafood and has a molecular weight measured in the hundreds of thousands, which corresponds to polymer chains in which several thousand units of monomers are linked together in the β-1,4 form. Chitosan obtained from fungal sources is typically of somewhat lower molecular weight and may contain fractions with molecular weight as low as 5O / 000 amu (units of atomic mass, daltons). For the present purposes, the term chitosan is proposed to apply to the copolymers of D-glucosamine and N-acetyl-D-glucosamine which contain 0-35% residues of N-acetyl-D-glucosamine and which have a higher molecular weight 50,000 amu and corresponding to the polymer chains in which approximately 250 or more monomer units are joined together (degree of polymerization or DP = 250). The chitosan used in this study was obtained from shrimp or crab shell and contained approximately 75-82% D-glucosamine residues, which is typical of commercially produced chitosan. It is easily soluble in dilute aqueous solutions of both mineral and carboxylic acids.

B. Composition of the Chitosan Oligomers The techniques are well known in the literature to cause the cleavage of chitosan chains using acid or enzyme catalysts. Depending on the starting material and the selected reaction conditions, the degree to which the chain cleavage occurs can be controlled so that the resulting fragments are still large enough to be considered as "chitosan (DP> 250). At the other extreme, the excision of the chain can be conducted under such stringent conditions that only the products are the monomeric species D-glucosamine and N-acetyl-D-glucosamine (DP = 1.) For the present purposes, the term "oligomers of Chitosan "is proposed to refer to those copolymers of D-glucosamine and N-acetyl-D-glucosamine which have a degree of polymerization (DP) of 2 to 50 corresponding to a molecular weight of about 320 to 10., 000 amu. Methods for preparing such oligomers of chitosan by acid catalysis have been described by Horowitz, Roseman, and Blumenthal (J. A., Chem. Soc., 1957, 79 / 5046-49). The processes for preparing such oligomers of chitosan by enzymatic cleavage have been described by Li, Brzezinski, and Beaulieu (Plant Physiol. Biochem., 1995, 33 (5), 599-603) The chitosan oligomers used in the present study are Prepared by a modification of the methods of Li, et al. A mixture of oligomers of chitosan and chitosan salt can be applied to the foliage of growing plants by spraying it with a solution containing appropriate amounts of these materials, or by other techniques which will be readily apparent to one skilled in the art.The preferred technique is by spraying the solution which eliminates the problems associated with the settling of the dispersions, or the danger of dust inhalation associated with the application of solids to the plant. It is preferred to use solutions having a salt concentration of chitosan (exclusive of the anion) of 0.01% to 1.5% and it is preferred to use s olutions with the concentration of 0.05 to 0.50%. The solutions in this concentration range have viscosities compatible with commercial spray equipment. In addition, these require an application rate of 22.73-227.3 liters (5-50 gallons) per application per acre to achieve a correct dose, which is compatible with the normal operation of commercial spray equipment. It is preferred to use solutions in which the guitosana oligomers are present in amounts equal to 0.05-50% and preferably 0.1-15%, based on the weight of chitosan salt therein (exclusive of the anion).

C. Acids Many of the acids that form water-soluble chitosan salts are themselves detrimental to growing plants, making it important to prevent plant exposure to high concentrations of these acids. On the other hand, unless a large excess of acid (measured as acid equivalents per mole of amino function in chitosan) is used to prepare the chitosan salt solution, chitosan dissolves only very slowly in the acidic solution at room temperature. One technique to solve this dilemma is to select only those more expensive acids which are less phytotoxic such as glutamic acid so that a large excess of acid can be used to form the solution while limiting the damage to the plant. A second technique is to employ a large excess of acid during the dissolution step and then neutralize the excess with the base after the dissolution is complete. This procedure is not satisfactory since more care is required to prevent pH excursions located in the region where the base is introduced. Such an excursion converts the chitosan salt back into electrically neutral chitosan which precipitates from the solution. The precipitate is then very slow to redissolve since there is no longer a large excess of acid present. Therefore, the preferred technique is to use only a very small excess of a cheap acid and to perform the dissolution step at elevated temperature. By limiting the excess acid used, the phytotoxic effect of the acid can be reduced to undetectable levels. Satisfactory dissolution rates can be achieved even with only a slight excess of acid upon dissolution at elevated temperature. It is more preferred to use acetic acid which is cheap and is readily available in a ratio of 1.02-1.20 moles of acetic acid per mole of amino groups in chitosan. This is in strict contrast to the teachings of U.S. Patent No. 4,812,159 and U.S. Patent No. 4,964,894 which found that the acid is phytotoxic and therefore unsuitable to form the chitosan solutions that are used for the applications described in US Pat. same. It is preferred to perform the dissolution step at 50-75C. In this form, chitosan can be dissolved in a 2.5% concentration in 3-5 hours. This concentration is suitable for efficient transport to the application site and is sufficiently strawy in viscosity that dilution at the site with water is direct. Suitable acids for making the chitosan salts for use in the invention are those which form water-soluble salts with chitosan. It is not necessary that the acid itself be soluble in water; however, such water soluble acids are preferred due to the ease in handling them. The inorganic acids that form the water-soluble chitosan salts include the halogen acids and nitric acid. The sulfuric and phosphoric acids are excluded because they do not form water-soluble salts with guitosana. Organic acids are preferred and include the following: lactic acid, glycolic acid, glutamic acid and acetic acid. Carboxylic acids can be used either mono or poly-functional, which can be aliphatic or aromatic, since these form water-soluble salts with chitosan.

D. Additives As used herein, the term "additives" refers to materials that can optionally be used to increase the effectiveness of the invention, but by themselves have no bio-activity. These include materials such as surfactants, wetting agents, defoaming agents, expanders, penetrating substances, activators, dispersing agents, diluents, odorants, polishing agents and the like. It is particularly preferred to use a small amount of wetting agent in the compositions in order to obtain even the distribution and wetting of the hydrophobic surface of the leaves of the plants Such agents are usually used in concentrations of 0.01-0.1% by weight .

E. Coadjuvants As used herein, the term "adjuvant" refers to materials that have a bio-activity that may be the same or different than the bio-activity of the chitosan salts. Such materials include fertilizers, fungicides, insect repellents, micronutrients, pesticides, herbicides and mixtures thereof. Both liquid and solid adjuvants can be used in conjunction with water-soluble chitosan salts and oligomers, since the resulting aqueous compositions can be sprayed.

F. Method for Making the Chitosan Oligomer / Chitosan Salt Solution A preferred method for making the treatment solution is to form an aqueous dispersion of guitosana at a temperature of 45-85 ° C (preferably 55-75 ° C) and then add the acid. Under these reaction conditions, the particle size of chitosan is not critical. It is preferred that the reaction temperature is at least 45C in order to have a rapid reaction rate without the need to use a large excess of acid. Otherwise, it is preferred that the reaction temperature does not exceed 85C in order to avoid discoloration and ensure the stability of the water soluble salt. Chitosan oligomers, additives and adjuvants can be added to the reaction solution at any stage. However, in order to minimize any of the side reactions, it is preferred that these be added after the reaction is complete and the solution has cooled.

G. Method for making the Chitosan Oligomers The chitosan oligomers were prepared by adding chitosanase enzyme (from actinomycete Ki tasatosporia N174) to a solution of chitosan acetate at 37-55C. After 31 hours, the mixture was heated to 85C to denature the enzyme. The product was concentrated under vacuum at 35-40 C and then lyophilized to dryness. Size exclusion chromatography on a Supelco-TSK G-Oligo-P Column with a mobile phase containing 0.03 M acetic acid and 0.2 M sodium sulfate revealed that 41% of the oligomers resolved were DP (polymerization degree) < 1 and 59% of DP 6-28.

H. Method of Application A clear advantage of the invention is that the chitosan / chitosan salt oligomer solution can be applied to the plants by spraying liquid, which is the most economical and efficient method of application for agricultural areas. large and small. The aqueous compositions can be applied by other liquid application methods such as brush application. However, these are less efficient. As mentioned above, the compositions of the invention are applied to the first true leaves of the growing plant and preferably at least twice again before harvesting the plant, preferably at flowering and at the beginning of ripening. It is not necessary to evaporate the applied solution. In fact, it is preferred not to do so for the reason that the adsorption of the chitosan salt and the chitosan oligomers in the plant takes place from the liquid state. However, the evaporation of the solution to dryness will ordinarily take place due to atmospheric, normal conditions of temperature and humidity.

I. Safety A further advantage of the invention is that the chitosan compositions are non-toxic. For example, chitosan glutamate has an oral, acute LD50 of more than 5 g / kg in rats (5 male albino rats, 5 female rats). In addition, the compositions have a dermal LD50, acute greater than 2 g / kg in rabbits (5 male albino rabbits, 5 females). Because of such low toxicity, the compositions of the invention are not toxic to birds, mammals, or humans. In addition, the low toxicity level and the easy biodegradability of the compositions act to prevent the detrimental effects on the beneficial constituents of the layers of fertile soil. Therefore, the EPA has established an exception to the requirement of a tolerance for poly-D-glucosamine residues, when these are used in the production of unprocessed agricultural products.

J. Test Procedures The following procedures were employed in the examples described below. "A '*' solution of chitosan acetate was prepared by vigorously stirring an appropriate amount of water at a temperature of 60C and adding small chitosan flakes containing 80% D-glucosamine residues at such a rate that the Chitosan becomes moistened and dispersed throughout the liquid phase. Glacial acetic acid was then added in the ratio of 163.4 g (0.36 pounds) of acetic acid per pound of chitosan. This represents a ratio of 1.03 equivalents of acetic acid per mole of amino function in chitosan. The mixture was stirred at 60C until substantially all of the chitosan had dissolved. The resulting solution was then filtered through thick gauze fabric to remove any foreign particles. The amounts of water and guitosana were selected so that the concentration of chitosan (exclusive of the acetate anion) was 0.5%. The chitosan oligomers, solids were added equivalent to 10% by weight of the chitosan (exclusive of the anion) and the mixture was stirred briefly to ensure the dissolution of the oligomers. This solution was then further diluted with water at a chitosan salt concentration of 2.5% by weight and packaged in units containing 304 g for transport to the test site. Dilution at the package site provided the correct amount of chitosan / chitosan salt oligomer solution to fill a 9,092 liter (2 gallon) garden sprayer with a solution containing 0.1% chitosan salt and 0.01% oligomers of chitosan. For crops that were planted as seed or tubers (pumpkin, corn, beans, potato), treatment was started as soon as the plant had produced its first set of true leaves. The true leaves are those that follow the emerging leaves (cotyledons) and resemble the leaves of the mature plant in shape. For the crops that were obtained as established greenhouse seedlings (tomatoes), the treatment was started at the time of the outdoor transplant. In any case, the treatment was repeated at intervals of two to three weeks throughout the growing season. The treatment protocol was to spray the foliage of the plant until the top of the leaf surfaces were completely moistened and the solution commented to drip from the tips of the leaves. To the extent possible, this treatment was performed just after the irrigation so that there was no substantial difference in the moisture available for the treated plants compared to the controls. When the plants increased in size, it was obviously necessary to use more solution of chitosan oligomer / chitosan salt to wet the leaves.The treatment ratio was estimated to be 22.73-45.46 liters (5-10 gallons) / acre for the treatment Initial and 90.92-181.84 liters (20-40 gallons) / acre at the end of the treatment.For crops that are optimally harvested before the ripening stage such as pumpkin, the number of fruits preferably that the total weight was used as a measure of increased production For crops that are harvested at maturity such as beans and corn, the total weight of the crop was used as a measure of increased production.

K. Treatable Plants A wide variety of cotyledonous plants can be advantageously treated by the method of the invention, since the treatment is carried out in the manner described above. Such plants include members of the genera Alli um, Appi um, Asparagus, Beta, Brassi ca, Capsi cum, Ci trullis, Cucurbi ta, Da ucus, Fxageria, Lactuca, Lycopersi cum, Phaseolus, Solanum, Spinachia and Zea. Among the members of these plant genera are asparagus, beans, beets, broccoli, carrots, celery, corn, eggplant, lettuce, melons, "onions, peas, peppers, potatoes, spinach, squash, strawberries and tomatoes.CJ.

EXAMPLES Example 1 Sideburns (Burpee Yellow Summer) were planted side by side each containing 3 plants at the end of May 1996 on land that had been prepared simply by turning and rotting clods. Cultivation and irrigation were applied to all stalks in identical form as required during growth. One stalk was treated with chitosan / chitosan salt oligomer solution by the procedure described above and the other served as control. Fruits were harvested when they reached the preferred size between July 9 and August 8. The study was completed on August 8 due to an infestation of barrenillos or weevils. The treated plants gave 40 fruits compared to 28 fruits for control. This represents an increase in yield of 43%.

Example 2 The parallel rows of beans or green beans were planted in an identical manner at the end of May 1996 on land that had been prepared by turning, plowing the clods, and flattening with rake, both rows were cultivated and irrigated as required. during growth One row was treated with chitosan / chitosan salt oligomer solution as described above while the other served as control The crop was harvested at weekly intervals until August 26 when the plants were judged to be The treated row produced 6,072 kg (13 pounds 6 ounces) of beans compared to 5,164 kg (11 pounds 6 ounces) for control, which represents an 18% yield increase.

Example 3 Tomatoes in seedlings (Brandywine) were transplanted outdoors on June 2, 1996, on land that had been prepared by cultivation and flattened with rake. One-third of the plants were treated with chitosan oligomer solution / chitosan salt as described above while the other half served as control. Both groups were grown, irrigated and supported in an equivalent manner as required throughout the growing season, and fruits were harvested when ripe. A total of 86 fruits were harvested from the treated plant group compared to 74 fruits from the control group. This represents a 16% performance increase.

Example 4 Two rows of ninety feet of sweet corn (Seneca Star) were planted on land that had been carved and flattened. One row was treated with chitosan oligomer solution / chitosan salt as described above while the other served as control.

The rows were grown under identical conditions and harvested during the period of July 20-July 29, 1996. The row processed produced 25,991 kg (57.25 pounds) (111 ears) of the product and the control produced 19,749 kg (43.50 pounds) (110 ears of corn) of the product. This represents a 32% performance increase.

EXAMPLE 5 One hundred cores of RED potatoes were divided into a test group and control group of 50 stings each and were cultured under identical conditions, except that the test group was treated with chitosan / chitosan salt oligomer solution as described above. The tubers were periodically examined and harvested as soon as they reached the target size. This was judged to have occurred on August 5, 1996, for the test group and the test plants were harvested accordingly resulting in 44,265 kg (97.50 pounds) of potatoes (average weight = 68.1 g (0.15 pounds)). The control group was harvested on August 14, 1996, which produced 37,296 kg (82.15 pounds) of potatoes (average weight = 57.6 g (0.127 pounds)). This represents an increase in yield of 19%, achieved in just 9 days of growth.

It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Having described the invention as above, the content of the following claims is claimed as property.

Claims (14)

1. A method for improving the yield of growing cotyledon plants having their first true leaves, characterized in that it comprises: (1) applying to the exposed surface of the leaves of the plant a liquid, aqueous solution having dissolved therein (a) 0.01-1.5% by weight of an anionic chitosan salt prepared by the reaction of chitosan having a molecular weight greater than 50,000 with an acid at a temperature of 45-85C, in which the solution of the molar ratio of acid to the amine groups in chitosan is 1.01-1.20 and (b) 0.05-50% ", based on the weight of the chitosan salt, excluding the anion, of chitosan oligomers having a molecular weight of 320-10,000 and (2) repeating step (1) at least one time before harvesting the plant.

2. A composition for treating cotyledonous plants which have their first true leaves, characterized in that it comprises an aqueous solution containing (a) 0.01-1.5% by weight of an anionic salt of chitosan prepared by the reaction of chitosan having a molecular weight greater than 50,000 at a temperature of 45-85 C with an acid, solution in which the molar ratio of equivalents of acid to amino groups derived from chitosan is 1.01-1.20 and (b) 0.05-50% by weight, based on the weight of the chitosan salt, exclusive of the anion, of chitosan oligomers having a molecular weight of 320-10,000.

3. A method for preparing the aqueous treatment solution according to claim 2, characterized in that it comprises: (a) forming an aqueous dispersion of chitosan by dispersing finely divided particles of chitosan in water having a molecular weight greater than 50,000 and adjusting the dispersion temperature at 45-85C; (b) adding an acid to the heated dispersion of step (a) in such an amount that the molar ratio of portions of acid to portions of amine in the dispersion is 1.01-1.20; (c) with stirring, maintain the temperature of the acidified solution from step (b) at 45-85C, for a sufficient time to effect the complete reaction of the chitosan with the acid, in this way a dissolved anionic chitosan salt is formed in the reaction solution; (d) with stirring, add the chitosan oligomers having a molecular weight of 320-10,000 to the chitosan salt solution of step (c) in an amount such that the chitosan oligomers are equivalent to 0.05-50% by weight of the dissolved chitosan salt; and (e) when necessary, adjust the water content of the chitosan salt / chitosan oligomer solution of step (d) to a level such that the concentration of chitosan salt therein is 0.01-1.5% by weight .

4. The method "according to claim 1, characterized in that the acid equivalents are derived from a carboxylic acid.

5. The method according to claim 4, characterized in that the carboxylic acid is selected from the group consisting of acetic, glutamic, lactic and glycolic acids and mixtures thereof.

6. The method according to claim 1, characterized in that at least a portion of the plant is edible to humans.

7. The method according to claim 6, characterized in that the plant is an edible vegetable.

8. The method according to claim 7, characterized in that the plant genus is selected from the group consisting of Allium, Apium, Asparagus, Beta, Brassi ca, Capsi cum, Ci trulli s, Cucurbi ta, Daucus, Frageria, Lactuca, Lycopersi cum, Phaseolus, Solanum, Spinachia and Zea.

9. The method according to claim 8, characterized in that the plant is selected from the group consisting of asparagus, beans, beets, broccoli, carrots, celery, corn, eggplant, lettuce, melons, onions, peas, peppers, potatoes, spinach, pumpkin, strawberries and tomatoes.

10. The method according to claim 9, characterized in that the plant is bean.

11. The method according to claim 9, characterized in that the plant is corn.

12. The method according to claim 9, characterized in that the plant is pumpkin.

13. The method according to claim 9, characterized in that the plant is potato.

14. The method according to claim 9, characterized in that the plant is tomato.