Methods for cultivating sweet potatoes and plant stimulants for sweet potato cultivation

Abstract

This invention provides a method for improving the yield of sweet potato harvests. [Solution] A method for cultivating sweet potatoes, comprising administering a plant stimulant containing exogenous elicitors and endogenous elicitors to seedlings at least once.

Description

【Technical Field】 【0001】 The present invention relates to a method for cultivating sweet potatoes using exogenous elicitors and endogenous elicitors, and a plant stimulant for cultivating sweet potatoes. 【Background Art】 【0002】 The yield of plants decreases due to abiotic stresses such as sunlight hours, temperature, and rainfall, as well as biotic stresses such as pests and diseases. For example, in the case of sweet potatoes, they are relatively resistant to high temperatures and drought and can grow well even in poor soil, but their growth is poor when the temperature drops significantly below the cultivation optimum temperature of 25 to 30°C. Also, under overly humid conditions, problems such as an increased likelihood of disease occurrence arise. In particular, in order to increase the yield of agricultural crops, various fertilizers and pesticides have been used until now. Fertilizers are nutrient sources required for plant growth but do not have the function of alleviating stress. Pesticides directly control pests parasitizing plants and eliminate biotic stress. However, when using pesticides, although their safety has been sufficiently confirmed, there are concerns about their effects on the human body and the environment due to excessive intake. In particular, chemicals such as pesticides manufactured by chemical synthesis methods may remain in the soil, etc. for a long time once sprayed, and it has been desired to confer resistance to biotic stress by other methods if possible. Therefore, in recent years, in addition to these, the use of biostimulants as substances safe for both the human body and the environment has attracted attention. 【0003】 Biostimulants, also known as biological stimulants or plant stimulants, contain various substances and microorganisms. When applied to plants or their root systems, they stimulate a series of processes that occur naturally within the crop, improving nutrient absorption, increasing fertilization efficiency, and conferring stress tolerance, thereby improving quality. Generally, even very small amounts stimulate plant vitality and promote growth. Applying biostimulants to plants is believed to increase nutrient absorption and utilization, promote growth, and improve crop yield and quality. Agricultural biostimulants include a diverse range of formulations, such as compounds, substances, and other products, that are applied to plants or soil to control and enhance the physiological processes of crops. Biostimulants act on plant physiology through pathways different from those of nutrients to improve crop vitality, yield, quality, and post-harvest shelf life. In this way, biostimulants can stimulate the inherent abilities of plants and promote their growth without causing the problems associated with conventional pesticides and fertilizers. 【0004】 In relation to such biostimulants, plant stimulants combining various oligosaccharides (Patent Document 1) and plant stimulants combining amino acids and oligosaccharides (Patent Document 2) have been reported. A method for efficiently cultivating cassava using plant stimulants (Patent Document 3) has also been reported. [Prior art documents] [Patent Documents] 【0005】 [Patent Document 1] Japanese Patent Publication No. 2024-081721 [Patent Document 2] Japanese Patent Publication No. 2024-088736 [Patent Document 3] Japanese Patent Publication No. 2022-024682 [Patent Document 4] International Publication No. 2017 / 104687 [Overview of the Initiative] [Problems that the invention aims to solve] 【0006】 However, in plant cultivation, the effects of plant stimulants vary depending on the plant species. Until now, the appropriate method for applying plant stimulants to sweet potatoes was unknown. [Means for solving the problem] 【0007】 This invention was made in view of the above circumstances, and in diligent research was conducted on how to administer plant stimulants in sweet potato cultivation. As a result, it was discovered that administering a plant stimulant containing exogenous and endogenetic elicitors to sweet potato seedlings significantly improves the yield of harvested produce, leading to the completion of this invention. 【0008】 In other words, the present invention encompasses the following [1] to

[23] . [1] A method for cultivating sweet potatoes, comprising administering a plant stimulant containing exogenous and endogenous elicitors to seedlings at least once. [2] The method for cultivating sweet potatoes according to [1], comprising immersing the cut ends of cuttings taken from seed potatoes in the plant stimulant for 5 to 48 hours. [3] A method for cultivating sweet potatoes according to [1] or [2], comprising giving the plant stimulant at least once to seedlings up to 30 days after planting sprouted seed potatoes in the field, or to seedlings up to 30 days after planting cuttings taken from seed potatoes in the field. [4] A method for cultivating sweet potatoes according to [1] or [2], further comprising administering the plant stimulant to the plant at least once after the seedling stage. [5] The method for cultivating sweet potatoes according to [1] or [2], wherein the exogenous elicitor is a chitin oligosaccharide and the endogenous elicitor is at least one oligosaccharide selected from cellooligosaccharides and xylooligosaccharides. [6] The method for cultivating sweet potatoes according to [1] or [2], wherein the mass ratio of the exogenous elicitor to the endogenous elicitor in the plant stimulant is 0.1 to 5. [7] A method for cultivating sweet potatoes according to [1] or [2], comprising xylooligosaccharide as the endogenous elicitor. [8] The method for cultivating sweet potatoes according to [7], comprising both cellooligosaccharides and xylooligosaccharides as the endogenous elicitors. [9] The method for cultivating sweet potatoes according to [8], wherein the mass ratio of cellooligosaccharide to xylooligosaccharide in the plant stimulant is 0.2 to 5.

[10] The method for cultivating sweet potatoes according to [1] or [2], wherein the plant stimulant is applied to the plant at a concentration such that the total content of the exogenous elicitor and the endogenous elicitor is 0.1 to 500 ppm by mass.

[11] The method for cultivating sweet potatoes according to [1] or [3], wherein the plant stimulant is applied to the plants by foliar spraying.

[12] A method for cultivating sweet potatoes using a plant stimulant comprising an exogenous elicitor and an endogenous elicitor, wherein the exogenous elicitor is a chitin oligosaccharide and the endogenous elicitor is at least one oligosaccharide selected from cellooligosaccharides and xylooligosaccharides, the plant stimulant being administered to seedlings at least once.

[13] A plant stimulant comprising an exogenous elicitor and an endogenous elicitor for use in the cultivation of sweet potatoes, which is applied to seedlings at least once.

[14] The plant stimulant described in

[13] , including being applied to cuttings before transplanting.

[15] The plant stimulant described in

[13] or

[14] , which is applied at least once to seedlings up to 30 days after transplanting sprouted seed potatoes into the field, or to seedlings up to 30 days after transplanting cuttings taken from seed potatoes into the field.

[16] The plant stimulant described in

[13] or

[14] , which is further applied to the plant at least once after the seedling stage.

[17] The plant stimulant according to

[13] or

[14] , wherein the exogenous elicitor is a chitin oligosaccharide and the endogenous elicitor is at least one oligosaccharide selected from cellooligosaccharides and xylooligosaccharides.

[18] The plant stimulant according to

[13] or

[14] , wherein the mass ratio of the exogenous elicitor to the endogenous elicitor in the plant stimulant is 0.1 to 5.

[19] The plant stimulant according to

[13] or

[14] , comprising xylooligosaccharide as the endogenous elicitor.

[20] The plant stimulant according to

[19] , comprising both cellooligosaccharide and xylooligosaccharide as the endogenous elicitor.

[21] The plant stimulant according to

[20] , wherein the mass ratio of cellooligosaccharide to xylooligosaccharide in the plant stimulant is 0.2 to 5.

[22] The plant stimulant according to

[13] or

[14] , which is applied to plants at a concentration such that the total content of the exogenous elicitor and the endogenous elicitor is 0.1 to 500 ppm by mass.

[23] The plant stimulant described in

[13] or

[14] , which is applied to plants by foliar spraying. [Effects of the Invention] 【0009】 The present invention provides a method for cultivating sweet potatoes in which a plant stimulant containing exogenous and endogenous elicitors is applied to young sweet potato seedlings, thereby improving the yield of harvested produce. [Modes for carrying out the invention] 【0010】 The embodiments of the present invention will be described below. The embodiments described below are representative examples of the present invention and are not limited to them. 【0011】 The sweet potato cultivation method of this embodiment includes applying a plant stimulant containing exogenous elicitors and endogenous elicitors to sweet potato seedlings. The "plant stimulant" includes not only those that mitigate abiotic stresses such as temperature, light, water, and salt that affect plant growth, but also those that mitigate biological stresses such as diseases and pests. 【0012】 An elicitor is a general term for substances that induce a biological defense response in tissues or cultured cells of higher plants, and induces disease resistance in the immune system of plants. Plants sense elicitors with receptors present on the leaf surface and initiate a pathogen resistance response. As a result, a biological defense action (immunity) in which various compounds are secreted occurs against various pathogens. When an elicitor acts on a plant, defense responses such as the synthesis and accumulation of phytoalexins and infection-specific proteins, the generation of reactive oxygen species, the generation of reactive nitrogen species, hypersensitive cell death, and changes in gene expression are induced, and it is thought that these reactions protect the plant from pathogens and enhance disease tolerance. Phytoalexins are antibacterial compounds synthesized and accumulated in plants by the action of elicitors, and the antibacterial compounds produced vary depending on the plant species. Representative phytoalexins include flavonoids, terpenoids, fatty acid derivatives, etc. Reactive oxygen species have the effect of killing pathogenic microorganisms, and furthermore, reactive oxygen species and reactive nitrogen species function as signals that initiate various defense reactions alone or in cooperation. Such disease resistance due to the elicitor effect is expected to be used in agriculture because it enhances resistance to a wide range of diseases. 【0013】 [Exogenous elicitor] In this specification, "exogenous elicitor" means an elicitor of substances derived from organisms other than plants, such as components derived from fungi, insects, and crustaceans, and is not particularly limited as long as it has an elicitor effect. Typically, they are chitin, chitosan, and their oligosaccharides, various biomolecules derived from insects, etc. The plant stimulant used in the cultivation method of sweet potato in this embodiment preferably contains chitosan oligosaccharide as an exogenous elicitor. 【0014】 Chitosan oligosaccharide may have a partial glucosamine structure but does not contain chitosan oligosaccharide. The chitosan oligosaccharide is an oligosaccharide in which several N-acetylglucosamines are linked, and generally, it is obtained by hydrolyzing chitin derived from crustaceans, etc., and is also referred to as oligo-N-acetylglucosamine. In other words, chitin oligosaccharides are obtained by chemically or enzymatically partially hydrolyzing chitin, which is prepared by conventional methods from the shells of crustaceans such as crabs and shrimp. Preferably, one or more of the following chitin oligosaccharides are used: N-acetylchitobiose, N-acetylchitotriose, N-acetylchitotetraose, N-acetylchitopentaose, N-acetylchitohexaose, N-acetylchitoheptaose, N-acetylchitooctaose, etc. Among these, N-acetylchitopentaose, N-acetylchitohexaose, and N-acetylchitoheptaose have particularly high elicitor effects. 【0015】 In this embodiment, the chitin oligosaccharide used is particularly preferably one having the following chemical structure. [ka] Furthermore, this includes cases where some of the acetyl groups (-COCH3) in the formula have been removed, with -NHCOCH3 becoming -NH2. The proportion of such deacetylation is preferably 30% or less of the total chitin oligosaccharide, more preferably 20% or less, and even more preferably 15% or less. 【0016】 [Endogenous Elicitor] In this specification, "endogenous elicitor" means an elicitor of plant origin, and is not particularly limited as long as it has an elicitor effect, but typically includes cellulose, xylan and their oligosaccharides produced from plants. The plant stimulant used in the sweet potato cultivation method of this embodiment preferably contains at least one oligosaccharide selected from cellooligosaccharides and xylooligosaccharides as an endogenous elicitor. 【0017】 Cello-oligosaccharides are short sugars in which multiple glucose molecules are polymerized by β-glycosidic bonds. In recent years, functionalities such as moisturizing properties, anti-stickiness, flavor enhancement, starch retrogradation reduction, and protein denaturation inhibition have been discovered, and their use in the pharmaceutical, cosmetic, food, and animal feed fields is expected. In particular, cello-oligosaccharides with a degree of polymerization of glucose of 3 or higher are attracting even greater attention in terms of increased functionality and the conferral of new functionalities. Cello-oligosaccharides currently used industrially are produced by enzymatic reactions, but their main components are glucose and the dimer cellobiose, and they contain almost no oligomers of the trimer cellotriose or higher. However, in recent years, the applicants have reported a method for producing cello-oligosaccharides containing oligomers with a degree of polymerization of glucose of 3 to 6 by controlling the heating rate, cooling rate, reaction temperature, and reaction time to induce a hydrothermal reaction in a hydrolysis reaction of plant biomass using a carbon catalyst (Patent Document 4). 【0018】 In this embodiment, the cellooligosaccharide used is particularly preferably one having the following chemical structure. [ka] 【0019】 Xylooligosaccharides are short sugars in which several xylose molecules are polymerized by β-glycosidic bonds. They are generally obtained by hydrolysis of xylan, the main component of hemicellulose, and are mainly sold for food applications. 【0020】 In this embodiment, xylooligosaccharides having the following chemical structure are particularly preferred. [ka] 【0021】 [Plant stimulant] The plant stimulant used in the sweet potato cultivation method of this embodiment contains at least the exogenous elicitor and the endogenous elicitor as active ingredients. The mass ratio of the exogenous elicitor to the endogenous elicitor in the plant stimulant (i.e., exogenous elicitor content / endogenous elicitor content) is preferably 0.1 to 5, more preferably 0.2 to 2, and even more preferably 0.3 to 0.6. 【0022】 The plant stimulant more preferably contains xylooligosaccharides as endogenous elicitors, and optimally contains both cellooligosaccharides and xylooligosaccharides. The mass ratio of cellooligosaccharides to xylooligosaccharides in the plant stimulant (i.e., cellooligosaccharide content / xylooligosaccharide content) is preferably 0.2 to 5, more preferably 0.3 to 3, and even more preferably 0.4 to 1.2. 【0023】 When a plant stimulant contains chitin oligosaccharides as an exogenous elicitor and both cellooligosaccharides and xylooligosaccharides as endogenous elicitors, the proportion of each oligosaccharide to the total content of chitin oligosaccharides, cellooligosaccharides, and xylooligosaccharides is preferably 10-50% by mass for chitin oligosaccharides, 10-50% by mass for cellooligosaccharides, and 10-60% by mass for xylooligosaccharides. More preferably, the proportion of each oligosaccharide is 20-40% by mass for chitin oligosaccharides, 20-40% by mass for cellooligosaccharides, and 20-55% by mass for xylooligosaccharides. 【0024】 The plant stimulant may further contain other components besides the exogenous and endogenous elicitors, which are the active ingredients, such as preservatives, spreading agents, anti-precipitation agents, thickeners, excipients, and solvents. Examples of preservatives include potassium sorbate, parahydroxybenzoic acid esters, benzoic acid, sodium dehydroacetate, hinokitiol, phenoxyethanol, polyaminopropyl biguanide, and polylysine. The spreading agent is a viscous liquid mainly composed of a surfactant and is not particularly limited as long as it can be used as a spreading agent for the plant stimulant, but examples include polyoxyethylene nonylphenyl ether, sorbitan fatty acid ester, and polyoxyethylene hexitane fatty acid ester. Examples of anti-precipitation agents include polyphosphate or salts of polyphosphate, or polycarboxylic acid-type polymer surfactants. Examples of thickeners include water-soluble polymers such as carboxymethylcellulose (CMC), polyacrylamide, and starch, or molasses, alcohol fermentation concentrate wastewater, and amino acid fermentation concentrate wastewater. Excipients include lactose and starch. Solvents are used to dilute the active ingredient to an appropriate concentration and to facilitate application to plants. Water is preferred as the solvent. 【0025】 The plant stimulant used in the sweet potato cultivation method of this embodiment may be in powder, granular, or liquid form, but generally, a liquid form that is easy to spray or immerse the plants in is preferred. When using a liquid plant stimulant, the concentration of the active ingredient in the plant stimulant at the time of spraying or immersion of the plants is preferably 0.1 to 500 ppm by mass, more preferably 0.5 to 200 ppm by mass, and even more preferably 1 to 100 ppm by mass. The concentration of the active ingredient in the plant stimulant refers to the total content of exogenous and endogenous elicitors in the plant stimulant. When the concentration at the time of spraying or immersion is 0.1 ppm by mass or higher, the effect of the plant stimulant is efficiently expressed. When the concentration at the time of spraying or immersion is 500 ppm by mass or lower, disease resistance can be expressed without inhibiting plant growth. 【0026】 While commercially available plant stimulants with pre-adjusted active ingredient concentrations may be used, typically, a plant stimulant stock solution containing high concentrations of exogenous and endogenous elicitors is diluted with water before use. When the plant stimulant stock solution is diluted (for example, 1000 times), the total content of exogenous and endogenous elicitors in the plant stimulant stock solution is preferably 0.05 to 10% by mass, more preferably 0.1 to 8% by mass, and even more preferably 0.5 to 6% by mass. 【0027】 [Sweet potato] The sweet potatoes cultivated using the cultivation method of this embodiment can be of various varieties, differing in skin color, flesh color, taste, etc., but are not particularly limited. In addition, sweet potatoes for processing and sweet potatoes for starch production can also be used in the same manner. 【0028】 [Cultivation method] There are no particular restrictions on the cultivation method of sweet potatoes, and methods such as sowing potatoes and growing from cuttings are possible, but growing from cuttings is preferred. 【0029】 For example, in the case of propagation by cuttings, the following methods can be used. Sweet potatoes are a hardy crop that is relatively resistant to high temperatures and drought and grows well even in poor soil. However, it is preferable to select a field in a temperate to subtropical region with an average temperature of 20-35°C and that is not excessively wet, and to transplant cuttings around May to June. Cuttings obtained by conventional methods can be used. The cultivation environment should be a field with plenty of sunlight, good ventilation, relatively dry conditions, and not excessive nutrients (especially nitrogen). It is preferable to deep plow the field beforehand and create ridges. Since drainage is important for sweet potato cultivation, it is preferable to make the ridges higher, at 20-30 cm. The ridge width should be 50-100 cm, and the spacing between ridges should be about 50-100 cm. Cut the seedlings for propagation to a length of 20-40 cm, plant them 20-50 cm apart and 5-20 cm deep, with the leaves above ground, and lightly press them down. There are no particular restrictions on planting methods, including vertical, diagonal, and horizontal planting. Roots will develop in about a week after planting, but it is preferable to follow conventional farming methods for management such as fertilizing, hilling, and watering until harvest. Remove the plants 120-150 days after planting and harvest the tubers at the base. 【0030】 The method for cultivating sweet potatoes according to this embodiment includes applying the plant stimulant to young seedlings. In this specification, "young seedlings" of sweet potatoes refer to seedlings up to 30 days after planting the sprouted seed potatoes in the field in the case of seed potato cultivation, and to cuttings taken from seed potatoes, and seedlings up to 30 days after planting the cuttings in the field in the case of cutting cultivation. 【0031】 In one embodiment, it is preferable to use the plant stimulant at least once on young seedlings 2 to 30 days after transplanting in cutting cultivation. It is more preferable to use the plant stimulant at least once on young seedlings 2 to 20 days after transplanting, even more preferable to use the plant stimulant at least once on young seedlings 2 to 10 days after transplanting, and even more preferable to use it once each on young seedlings 2 to 10 days and 15 to 30 days after transplanting. To obtain more robust seedlings, it is particularly preferable to further apply the plant stimulant by immersing the cut end of the cuttings in it for 5 to 48 hours before transplanting. Furthermore, it is preferable to apply the plant stimulant at least once on young seedlings 2 to 30 days after transplanting, and then apply it to the plant at least once every 10 to 20 days thereafter. 【0032】 In another embodiment of the sweet potato cultivation method of this embodiment, it is preferable to further apply the plant stimulant to the plant after the seedling stage. In this specification, "plant after the seedling stage" of sweet potatoes refers to the plant after the seedling stage, that is, the plant 30 days or more after transplanting. 【0033】 In one embodiment, it is preferable to use the plant stimulant at least once on the plant after the seedling stage. It is more preferable to use it once every 10 to 20 days until about 90 days after transplanting. 【0034】 (Application of plant stimulants) The application of plant stimulants to sweet potatoes can be carried out by methods customary in this industry, and the method of application is not particularly limited. For example, it may be applied directly to the leaves and stems of the plants, applied to the culture medium or soil in which the plants are grown, or mixed with fertilizers and applied to the culture medium or soil. As for the application method, foliar application is particularly preferable for effectively expressing elicitor activity. Foliar application can be carried out by methods customary in this industry, such as power sprayers, shoulder sprayers, broadcasters, sprayers, manned or unmanned helicopters, fogging devices, hand sprayers, etc. 【0035】 The amount of plant stimulant to be sprayed is approximately 1 cm above the leaf surface. 2 Preferably, the amount of active ingredient sprayed per unit area is 0.1 ng to 100 ng, and the amount per 1 cm of leaf surface. 2 It is more preferable that the amount of active ingredient applied per unit area is 1 ng to 20 ng. In actual fields, it is difficult to selectively apply only to the leaf surface and to ensure that all of the applied substance adheres to the leaf surface, so for a cultivated area of ​​100 m² 2 It is preferable to dilute 0.01g to 20g of the active ingredient per unit area so that the concentration in the plant stimulant is 1 ppm to 100 ppm by mass, and then evenly spray it over the plant. More preferably, for a cultivated area of ​​100m² 2 It is preferable to dilute 0.1g to 10g of the active ingredient per unit so that the concentration in the plant stimulant is 10 ppm to 500 ppm by mass. 【0036】 In the sweet potato cultivation method of this embodiment, soil management is preferably carried out using conventional farming methods. 【0037】 (Effects of plant stimulants) The sweet potato cultivation method of this embodiment includes administering a plant stimulant containing exogenous and endogenous elicitors to sweet potato seedlings. Furthermore, it is preferable to continue administering the plant stimulant containing exogenous and endogenous elicitors to the plant after the seedling stage. The reason why administering a plant stimulant with this configuration at this stage is effective is not yet fully understood. By administering exogenous elicitors (e.g., derived from chitin oligosaccharides), the plant is given resistance to herbivore-derived diseases, etc., but it is thought that excessive action may inhibit growth. On the other hand, by administering endogenous elicitors (e.g., derived from cellooligosaccharides and xylooligosaccharides), the plant is expected to recognize its own cell damage and disruption components (DAMPs: damage-associated molecular patterns), thereby promoting its own growth in order to acquire immunity and repair cells. In the sweet potato cultivation method of this embodiment, it is believed that by applying a plant stimulant containing exogenous and endogenous elicitors, particularly during the early seedling stage, robust seedlings with disease resistance can be cultivated while suppressing growth inhibition. By subsequently applying the plant stimulant to the strong plants thus cultivated, the growth-promoting effect of the endogenous elicitor can be utilized without being strongly affected by the growth-inhibiting effect of the exogenous elicitor, and ultimately, a high growth effect can be achieved through the complementary action of both. Therefore, when cultivating sweet potatoes, it is estimated that applying the plant stimulant at least once to seedlings after transplanting, and preferably to seedlings before transplanting, strongly promotes the rooting of adventitious roots (roots that thicken and become potatoes), and further applying the plant stimulant at least once to plants after the seedling stage promotes strong plant growth, accelerates the thickening of adventitious roots, and improves the yield of harvested products. 【0038】 The present invention will be further illustrated by the following examples, but the present invention is not limited thereto. [Examples] 【0039】 [1. Prepare the oligosaccharides] (1) Chitin oligosaccharide 10 g of chitin powder (Wako Pure Chemical Industries, purified chitin) was dispersed in 30 mL of water containing 1.2 g of 85% phosphoric acid (Wako Pure Chemical Industries, special grade reagent). The powder was then dried under reduced pressure and placed in a 250 mL alumina pot along with 100 g of 5 mm diameter alumina balls. This pot was then set in a planetary ball mill (Fritsch, PULVERISETTE 6) and processed continuously at 500 rpm for 6 hours to obtain the reaction product. The reaction was started at room temperature, and the temperature rise due to shear heating was left to occur naturally. Next, the reaction mixture was suspended in water and neutralized with calcium hydroxide to obtain a slurry. This slurry was then filtered using 5B filter paper in a Nutsche filter, and the recovered filtrate was freeze-dried to obtain chitin oligosaccharide powder. 【0040】 (2) Cellooligosaccharides 271g of cotton linter pulp (from China, cellulose content 97%) (moisture content 1.8%, dry weight 266g) was mixed with 38g of 85% by mass phosphoric acid (special grade reagent manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) using a food blender (model: HBF500S, Hamilton Beach Corporation) to obtain 309g of reaction material (moisture content 3.4%, phosphoric acid content 10.4%). Next, 309g of the reaction material was placed in a vibrating mill (device name: MB-1 type, manufactured by Chuo Kakoki Co., Ltd., pot size 5L) together with 13kg of φ3 / 4 inch carbon steel balls. A hydrolysis reaction was carried out by dry grinding for 24 hours under conditions of a total amplitude of 8mm, a vibration frequency of 16.2Hz, and a jacket flow water temperature of 75℃, after which the reaction powder was recovered. 10 g of this reaction powder and 90 g of deionized water were placed in a 200 L beaker and stirred at 25°C for 1 hour using a magnetic stirrer to obtain an extract of cellulose hydrolysate. Next, 1.3 g of a 40% by mass aqueous calcium hydroxide solution was added to the extract, and the mixture was stirred using a magnetic stirrer at 25°C for 1 hour to prepare a neutralized solution. The supernatant was collected using a centrifuge, and then freeze-dried to obtain cellooligosaccharide powder. 【0041】 (3) Xylooligosaccharides Acremonium Cellulolyticus The cus)TN strain (FERM P-18508) was cultured in a 500mL flask containing 100mL of liquid medium (Avicel 50g / L, KH2O4 24g / L, ammonium sulfate 5g / L, potassium tartrate 1 / 2H2O 4.7g / L, urea 4g / L, Tween80 1g / L, MgSO4·7H2O 1.2g / L, ZnSO4·7H2O 10mg / L, MnSO4·5H2O 10mg / L, CuSO4·5H2O 10mg / L) at 30°C for 6 days with shaking. 5g of corn cob powder was suspended in 50mL of the supernatant from the resulting culture solution and stirred at 50°C for 72 hours. The supernatant from the resulting reaction solution was freeze-dried to obtain xylooligosaccharide powder. 【0042】 [2. Cultivating sweet potatoes] (1) Preparation of plant stimulants The oligosaccharides prepared in [1. Preparation of Oligosaccharides] were dissolved in water by stirring with a stirrer at their respective composition ratios so that the concentration of the active ingredient (mass ppm) in the plant stimulants shown in Examples 1-11 and Comparative Examples 1-5 in Table 1 was 1000 times greater. After dissolving in water, the solution was sterilized using a 0.45 μm filter to obtain the plant stimulant stock solution. This stock solution was diluted 1000 times with water and used in the following cultivation tests. Hereafter, the plant stimulant after being diluted 1000 times may be referred to as the "plant stimulant dilution." Note that the composition ratios of each oligosaccharide in the table are expressed in mass percent. 【0043】 (2) Cultivation Test 1 (Examples 1-25, Comparative Examples 1-11) Sweet potato field cultivation was carried out in a field inside a plastic greenhouse. Two weeks before the planned planting date, the field was tilled, and ridges were created with a width of 80 cm, a spacing of 80 cm between ridges, and a height of 25 cm. Sweet potato cuttings (Beniharuka and Silk Sweet varieties) (approximately 30 cm long) were planted at an angle at a depth of 10-12 cm at 30 cm intervals. After lightly pressing down and watering thoroughly, the plants gradually took root after 5-7 days. These were then divided into 27 plots of 5 plants each, and conventional farming methods were used. Seedlings (cuttings) before transplanting, seedlings after transplanting, and plants after the seedling stage were treated by immersion in a diluted plant stimulant solution or by spraying it onto the leaves and soil until they were moist, under the conditions described in Tables 1 to 3. The immersion treatment of cuttings before transplanting was performed by immersing the cut ends of the cuttings in the diluted plant stimulant solution in a container for 24 hours. For the spray treatment of young seedlings after transplanting and for plants after the seedling stage, the diluted plant stimulant solution was prepared at a rate of 1 kg / plot / application and applied as a foliar spray using a watering can and by irrigating the soil around the base of the plants, as shown in Table 1. Harvesting was performed 140 days after transplanting, and the average yield for each plot (5 plants) was measured and compared under each condition. The yield was measured by harvesting the edible tubers (potatoes) from the base of the plant and measuring the average weight of tubers within the standard size (2S to 3L) per plant. The test results are shown in Tables 1 to 3. 【0044】 [Table 1] 【0045】 [Table 2] 【0046】 [Table 3] 【0047】 The results in Tables 1-3 show that in sweet potato cultivation, using a plant stimulant containing both exogenous and endogenous elicitors on young seedlings significantly improved yield. Although not shown in the data, there was a tendency for an increase in medium to 2L sized potatoes, especially when used on seedlings after transplanting. The reason for this is unclear, but it is presumed that using it 1-3 times within 30 days of transplanting promotes the rooting and growth of adventitious roots. In addition, while using only one type of endogenous elicitor in addition to an exogenous elicitor was sufficiently effective, using two types of endogenous elicitors in combination yielded even better results.

Claims

[Claim 1] A method for cultivating sweet potatoes, comprising administering a plant stimulant containing exogenous and endogenous elicitors to seedlings at least once. [Claim 2] A method for cultivating sweet potatoes according to claim 1, comprising immersing the cut end of a cutting taken from a seed potato in the aforementioned plant stimulant for 5 to 48 hours. [Claim 3] A method for cultivating sweet potatoes according to claim 1 or 2, comprising applying the plant stimulant at least once to seedlings up to 30 days after planting sprouted seed potatoes in the field, or to seedlings up to 30 days after planting cuttings taken from seed potatoes in the field. [Claim 4] A method for cultivating sweet potatoes according to claim 1 or 2, further comprising administering the plant stimulant to the plant at least once after the seedling stage. [Claim 5] The method for cultivating sweet potatoes according to claim 1 or 2, wherein the exogenous elicitor is a chitin oligosaccharide, and the endogenous elicitor is at least one oligosaccharide selected from cellooligosaccharides and xylooligosaccharides. [Claim 6] The method for cultivating sweet potatoes according to claim 1 or 2, wherein the mass ratio of the exogenous elicitor to the endogenous elicitor in the plant stimulant is 0.1 to 5. [Claim 7] A method for cultivating sweet potatoes according to claim 1 or 2, wherein the endogenous elicitor comprises xylooligosaccharide. [Claim 8] The method for cultivating sweet potatoes according to claim 7, wherein the endogenous elicitor includes both cellooligosaccharides and xylooligosaccharides. [Claim 9] The method for cultivating sweet potatoes according to claim 8, wherein the mass ratio of cellooligosaccharide to xylooligosaccharide in the plant stimulant is 0.2 to 5. [Claim 10] The method for cultivating sweet potatoes according to claim 1 or 2, wherein the plant stimulant is applied to the plant at a concentration such that the total content of the exogenous elicitor and the endogenous elicitor is 0.1 to 500 ppm by mass. [Claim 11] The method for cultivating sweet potatoes according to claim 1 or 3, wherein the plant stimulant is applied to the plants by foliar spraying. [Claim 12] A method for cultivating sweet potatoes using a plant stimulant containing an exogenous elicitor and an endogenous elicitor, wherein the exogenous elicitor is a chitin oligosaccharide and the endogenous elicitor is at least one oligosaccharide selected from cellooligosaccharides and xylooligosaccharides, and the plant stimulant is administered to seedlings at least once. [Claim 13] A plant stimulant containing an exogenous elicitor and an endogenous elicitor, used in the cultivation of sweet potatoes, which is applied to seedlings at least once. [Claim 14] The plant stimulant according to claim 13, which includes being applied to cuttings before transplanting. [Claim 15] The plant stimulant according to claim 13 or 14, which is applied at least once to seedlings up to 30 days after planting sprouted seed potatoes in the field, or to seedlings up to 30 days after planting cuttings taken from seed potatoes in the field. [Claim 16] Furthermore, the plant stimulant according to claim 13 or 14, which is applied at least once to the plant body after the seedling stage. [Claim 17] The plant stimulant according to claim 13 or 14, wherein the exogenous elicitor is a chitin oligosaccharide, and the endogenous elicitor is at least one oligosaccharide selected from cellooligosaccharides and xylooligosaccharides. [Claim 18] The plant stimulant according to claim 13 or 14, wherein the mass ratio of the exogenous elicitor to the endogenous elicitor in the plant stimulant is 0.1 to 5. [Claim 19] The plant stimulant according to claim 13 or 14, comprising xylooligosaccharide as the endogenous elicitor. [Claim 20] The plant stimulant according to claim 19, comprising both cellooligosaccharides and xylooligosaccharides as the endogenous elicitor. [Claim 21] The plant stimulant according to claim 20, wherein the mass ratio of cellooligosaccharide to xylooligosaccharide in the plant stimulant is 0.2 to 5. [Claim 22] The plant stimulant according to claim 13 or 14, which is applied to plants at a concentration such that the total content of the exogenous elicitor and the endogenous elicitor is 0.1 to 500 ppm by mass. [Claim 23] A plant stimulant according to claim 13 or 14, which is applied to plants by foliar spraying.

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