Method for cultivating sweet potato and plant stimulant for cultivating sweet potato

Abstract

The present invention provides a method for increasing the yield of harvested products of sweet potato. The solution is a cultivation method for sweet potato, comprising: applying at least once to seedlings a plant stimulant containing an exogenous elicitor and an endogenous elicitor.

Description

Technical Field

[0001] This invention relates to a method for cultivating sweet potatoes using exogenous and endogenous elicitors, and to plant stimulants for sweet potato cultivation. Background Technology

[0002] Plant yields are reduced due to abiotic stresses such as sunlight duration, temperature, and rainfall, as well as biotic stresses such as diseases and pests. For example, sweet potatoes, although a robust crop that is relatively tolerant of high temperatures and drought and can grow well in poor soil, show poor growth and development if the temperature drops significantly below the optimal cultivation temperature of 25-30°C. Furthermore, excessively wet conditions can lead to increased susceptibility to diseases. To date, various fertilizers and pesticides have been used, particularly to increase crop yields. While fertilizers provide essential nutrients for plant growth, they do not mitigate stress. Pesticides, while directly eliminating pests and diseases that parasitize plants and relieving biotic stress, raise concerns about the potential impacts on humans and the environment from excessive use, despite well-established safety profiles. This is especially true for chemically synthesized pesticides, which may persist in the soil for extended periods after release. Therefore, it is desirable to develop alternative methods to enhance tolerance to biotic stresses. Therefore, in recent years, in addition to these substances, the use of biostimulants, which are safe for both humans and the environment, has attracted attention.

[0003] "Biostimulants," also known as "bioenergetic agents" or "plant vitality agents," contain any group of substances / microorganisms that, when applied to plants or their roots, stimulate a series of processes that occur naturally within the crop. These stimulations can improve nutrient absorption, increase fertilization efficiency, and impart stress tolerance, thus enhancing quality. Generally, very small amounts are used to stimulate plant vitality and promote growth and development. It is believed that by applying biostimulants to plants, nutrient absorption and utilization rates are improved, growth and development are promoted, and crop yield and quality are enhanced. Agricultural biostimulants include a wide variety of formulations, such as compounds, substances, and other products, applied to plants or soil to control / enhance crop physiological processes. To improve crop vitality, yield, quality, and post-harvest preservation, biostimulants act on plant physiology through pathways different from nutrients.

[0004] In this way, by using biostimulants, the problems caused by pesticides and fertilizers in the past can be avoided, and the plant's inherent ability can be stimulated to promote its growth.

[0005] As substances related to such biostimulants, plant activators composed of various oligosaccharides have been reported to date (Patent Document 1), and plant activators utilizing combinations of amino acids and oligosaccharides (Patent Document 2). Additionally, methods for effectively cultivating cassava using plant activators have been reported (Patent Document 3).

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Application Publication No. 2024-081721

[0009] Patent Document 2: Japanese Patent Application Publication No. 2024-088736

[0010] Patent Document 3: Japanese Patent Application Publication No. 2022-024682

[0011] Patent Document 4: International Publication No. 2017 / 104687 Summary of the Invention

[0012] The problem that the invention aims to solve

[0013] However, in plant cultivation, the effectiveness of plant stimulants varies depending on the plant species. To date, the appropriate application method for plant stimulants for sweet potatoes remains unknown.

[0014] Methods for solving problems

[0015] This invention was proposed in view of the above-mentioned circumstances, based on repeated and in-depth research on the application methods of plant stimulants in sweet potato cultivation. The results showed that by applying plant stimulants containing exogenous and endogenous elicitors to sweet potato seedlings, the yield of the harvest was significantly increased, thus completing this invention.

[0016] That is, the present invention includes the following [1] to

[23] .

[0017] [1] A method of cultivating sweet potato, including applying a plant stimulant containing exogenous and endogenous elicitors to seedlings at least once.

[0018] [2] The sweet potato cultivation method according to [1] includes: soaking the plant stimulant in the cut of the cuttings collected from the seed potato for 5 to 48 hours.

[0019] [3] The sweet potato cultivation method according to [1] or [2] includes: applying the plant stimulant at least once to seedlings within 30 days after the sprouted seed potatoes are transplanted into the field, or to seedlings within 30 days after the cuttings collected from the seed potatoes are transplanted into the field.

[0020] [4] The sweet potato cultivation method according to [1] or [2] includes: further applying the plant stimulant to the plant body at least once after the seedling stage.

[0021] [5] According to the sweet potato cultivation method described in [1] or [2], the exogenous elicitor is a chitin oligosaccharide, and the endogenous elicitor is selected from at least one oligosaccharide among cellulosic oligosaccharides and xylooligosaccharides.

[0022] [6] According to the sweet potato cultivation method described in [1] or [2], the mass ratio of the exogenous elicitor to the endogenous elicitor in the plant stimulant is 0.1 to 5.

[0023] [7] According to the sweet potato cultivation method described in [1] or [2], the endogenous elicitor contains xylooligosaccharides.

[0024] [8] According to the sweet potato cultivation method described in [7], the endogenous elicitor includes both cellulosic sugar and xylooligosic sugar.

[0025] [9] According to the sweet potato cultivation method described in [8], the mass ratio of the fiber oligosaccharide to the xylooligosaccharide in the plant stimulant is 0.2 to 5.

[0026]

[10] According to the sweet potato cultivation method described in [1] or [2], the plant stimulant is applied to the plant at a concentration of 0.1 to 500 ppm by mass, where the total content of the exogenous elicitor and the endogenous elicitor is 0.1 to 500 ppm by mass.

[0027]

[11] The plant stimulant is applied to the plant by foliar dispersal according to the sweet potato cultivation method described in [1] or [3].

[0028]

[12] The cultivation method of sweet potato is a cultivation method in which a plant stimulant containing exogenous elicitors and endogenous elicitors is used in the cultivation of sweet potato seed tubers, wherein the method includes: applying the plant stimulant to the seedlings at least once, wherein the exogenous elicitor of the plant stimulant is a chitinous oligosaccharide, and the endogenous elicitor is at least one oligosaccharide selected from cellulose oligosaccharides and xylooligosaccharides.

[0029]

[13] Plant stimulants are plant stimulants used in the cultivation of sweet potatoes that contain exogenous and endogenous elicitors and are applied to seedlings at least once.

[0030]

[14] Apply the plant stimulant as described in

[13] to the cuttings before transplanting.

[0031]

[15] The plant stimulant according to

[13] or

[14] shall be applied at least once to seedlings within 30 days after the sprouted seed potatoes are transplanted into the field, or to seedlings within 30 days after the cuttings collected from the seed potatoes are transplanted into the field.

[0032]

[16] The plant stimulant described in

[13] or

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

[0033]

[17] According to the plant stimulant of

[13] or

[14] , the exogenous elicitor is a chitinous oligosaccharide, and the endogenous elicitor is at least one oligosaccharide selected from cellulose oligosaccharides and xylooligosaccharides.

[0034]

[18] According to the plant stimulant of

[13] or

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

[0035]

[19] The plant stimulant according to

[13] or

[14] contains xylooligosaccharides as the endogenous elicitor.

[0036]

[20] The plant stimulant according to

[19] comprises both cellulosic sugar and xylooligosic sugar as the endogenous elicitor.

[0037]

[21] According to the plant stimulant of

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

[0038]

[22] The plant stimulant according to

[13] or

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

[0039]

[23] The plant stimulant described in

[13] or

[14] is applied to the plant by foliar dispersal.

[0040] The effects of the invention

[0041] The sweet potato cultivation method of the present invention can increase the yield of the harvest by applying a plant stimulant containing exogenous and endogenous elicitors to the sweet potato seedlings. Detailed Implementation

[0042] Hereinafter, embodiments of the present invention will be described. Furthermore, the embodiments described below show representative examples of the present invention and are not limited to them.

[0043] The sweet potato cultivation method of this embodiment includes applying a plant stimulant containing exogenous and endogenous elicitors to sweet potato seedlings. The "plant stimulant" includes not only substances that have a mitigating effect on abiotic stresses such as temperature, light, water, and salt related to plant growth and development, but also substances that have a mitigating effect on biotic stresses such as diseases and pests.

[0044] Elicitors are a general term for substances in higher plant tissues or cultured cells that induce defensive responses in organisms, contributing to disease resistance within the plant's immune mechanism. Plants use receptors on leaf surfaces and other surfaces to sense elicitors and initiate pathogen resistance responses. This results in the secretion of various compounds as a form of biological defense (immunity) against different pathogens. It can be considered that if elicitors act on plants, they induce defensive responses such as the synthesis / accumulation of plant antitoxins and infection-specific proteins, the generation of reactive oxygen species (ROS) and reactive nitrogen species (RNN), hypersensitive cell death, and changes in gene expression. Through these responses, plants protect themselves from pathogens and enhance their disease resistance.

[0045] Phytotoxicants are antimicrobial compounds synthesized and accumulated within plants through the action of elicitors; the specific antimicrobial compounds produced vary from plant to plant. Representative phytotoxicants include flavonoids, terpenes, and fatty acid derivatives. Reactive oxygen species (ROS) have the effect of killing pathogenic microorganisms. Furthermore, ROS and reactive nitrogen species, alone or in synergy, act as signals to initiate various defense responses. The disease resistance resulting from such elicitor effects is enhanced against a wide range of diseases, and therefore, their application in agriculture is anticipated.

[0046] [Exogenous elicitors]

[0047] In this specification, the term "exogenous elicitor" refers to substances derived from organisms other than plants, such as elicitors derived from fungi, insects, and crustaceans. There are no particular restrictions as long as they have an elicitor effect, but typical examples include chitin, deacetylated chitin and their oligosaccharides, and a variety of biomolecules derived from insects.

[0048] The plant stimulant used in the sweet potato cultivation method of this embodiment preferably contains chitin oligosaccharides as exogenous elicitors.

[0049] Chitin oligosaccharides may contain a partial glucosamine structure, but do not include deacetylated chitin oligosaccharides. These chitin oligosaccharides are oligosaccharides formed by the linkage of several N-acetylglucosamine molecules. Generally, they are obtained by hydrolyzing chitin derived from crustaceans or similar sources, and are also known as oligo-N-acetylglucosamine.

[0050] That is, chitin oligosaccharides are obtained by chemically or enzymatically partially hydrolyzing chitin, which is prepared from the shells of crustaceans such as crabs and shrimp, using conventional methods. As chitin oligosaccharides, one or more mixtures selected from N-acetylchitobiose, N-acetylchitotriose, N-acetylchitotetraose, N-acetylchitopentose, N-acetylchitohexaose, N-acetylchitoheptaose, and N-acetylchitooctaose are preferred. Among these, N-acetylchitopentose, N-acetylchitohexaose, and N-acetylchitoheptaose have particularly high exciton effects.

[0051] The chitin oligosaccharide used in this embodiment is particularly preferably a substance having the following chemical structure.

[0052]

[0053] This also includes substances in which the acetyl group (-COCH3) in the formula is partially removed, and -NHCOCH3 is changed to -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.

[0054] [Endogenous elicitors]

[0055] In this specification, the term "endogenous elicitor" refers to an elicitor derived from plant substances. There are no particular restrictions as long as it has an elicitor effect, but typically it includes cellulose, xylan and their oligosaccharides produced from plants.

[0056] The plant stimulant used in the sweet potato cultivation method of this embodiment preferably contains at least one oligosaccharide selected from fiber oligosaccharides and xylooligosaccharides as an endogenous elicitor.

[0057] Cellulose oligosaccharides are oligosaccharides formed by the polymerization of multiple glucose molecules through β-glycosidic bonds. In recent years, they have been found to possess functionalities such as moisturizing properties, inhibition of stickiness, imparting a refreshing taste, reducing starch retrogradation, and inhibiting protein denaturation, and are expected to be used in the pharmaceutical, cosmetic, food, and animal feed industries. In particular, cellulose oligosaccharides with a degree of polymerization of glucose of 3 or higher are expected to have greater potential for enhancing these functionalities and imparting new functionalities. Currently, industrially used cellulose oligosaccharides are manufactured through enzymatic reactions, but their main components are glucose and cellobiose as dimers, containing almost no oligomers of cellotriose or higher as trimers. However, in recent years, the applicant has reported a method for manufacturing cellulose oligosaccharides containing oligomers of glucose with a degree of polymerization of 3 to 6 by controlling the heating rate, cooling rate, reaction temperature, and reaction time during the hydrolysis reaction of plant biomass using a carbon catalyst to carry out the hydrothermal reaction (Patent Document 7).

[0058] The cellulose oligosaccharides used in this embodiment are particularly preferred to be substances having the following chemical structure.

[0059]

[0060] Xylooligosaccharides are oligosaccharides formed by the polymerization of several xyloses through β-glycosidic bonds. Generally, they are obtained by hydrolyzing xylan, the main component of hemicellulose, and are mainly sold for food purposes.

[0061] The xylooligosaccharides used in this embodiment are particularly preferred to be substances having the following chemical structure.

[0062]

[0063] [Plant stimulants]

[0064] The plant stimulant used in the sweet potato cultivation method of this embodiment comprises, as an active ingredient, at least the exogenous elicitor and the endogenous elicitor. 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.

[0065] Plant stimulants are more suitable as endogenous elicitors comprising xylooligosaccharides, and most preferably comprised of both cellulosaccharides and xylooligosaccharides. The mass ratio of the cellulosaccharides to the xylooligosaccharides in the plant stimulant (i.e., cellulosaccharide content / xylooligosaccharide content) is preferably 0.2–5, more preferably 0.3–3, and even more preferably 0.4–1.2.

[0066] When the plant stimulant contains chitin oligosaccharides as exogenous elicitors and both cellulosic oligosaccharides and xylooligosaccharides as endogenous elicitors, the preferred ratio of each oligosaccharide to the total content of chitin oligosaccharides, cellulosic oligosaccharides, and xylooligosaccharides is 10-50% by mass for chitin oligosaccharides, 10-50% by mass for cellulosic oligosaccharides, and 10-60% by mass for xylooligosaccharides. More preferably, the ratio of each oligosaccharide is 20-40% by mass for chitin oligosaccharides, 20-40% by mass for cellulosic oligosaccharides, and 20-55% by mass for xylooligosaccharides.

[0067] Plant stimulants can further include components other than exogenous and endogenous elicitors as active ingredients, such as preservatives, spreading agents, suspending agents, thickeners, excipients, and solvents. Examples of preservatives include potassium sorbate, parabens, benzoin, sodium dehydroacetate, juniper alcohol, phenoxyethanol, polyaminopropyl biguanide, and polylysine. Spreading agents are viscous liquids with surfactants as the main component; there are no particular restrictions as long as they can be used as spreading agents for plant stimulants. Examples include polyoxyethylene nonylphenyl ether, sorbitol fatty acid esters, and polyoxyethylene hexityl anhydride fatty acid esters. Examples of suspending agents include polyphosphates or their salts, or polycarboxylic acid type polymeric surfactants. Examples of thickeners include carboxymethyl cellulose (CMC), polyacrylamide, water-soluble polymers such as starch, or waste molasses, concentrated ethanol fermentation liquid, and concentrated amino acid fermentation liquid. Examples of excipients include lactose and starch. Solvents are used to dilute the active ingredient to an appropriate concentration into a liquid form, facilitating its dispersal onto plants. Water is preferred as a solvent.

[0068] The plant stimulant used in the sweet potato cultivation method of this embodiment can be any of the following: powder, granules, or liquid, but is generally preferred to be a liquid that is easy to disperse or soak. When using a liquid plant stimulant, the concentration of the active ingredient in the plant stimulant during dispersal or soaking of the plant 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. Furthermore, the concentration of the active ingredient in the plant stimulant refers to the total content of exogenous and endogenous elicitors in the plant stimulant. If the concentration during dispersal or soaking is 0.1 ppm by mass or higher, the plant stimulant effectively exhibits its effects. If the concentration during dispersal or soaking is 500 ppm by mass or lower, disease resistance can be achieved without inhibiting plant growth.

[0069] Plant stimulants can be commercially available products prepared in advance at the concentrations mentioned above, but typically, they are used by diluting a high-concentration plant stimulant stock solution containing both exogenous and endogenous elicitors with water. When using a plant stimulant stock solution diluted (e.g., to 1000 times), the total content of exogenous and endogenous elicitors in the plant stimulant stock solution is preferably 0.05–10% by mass, more preferably 0.1–8% by mass, and even more preferably 0.5–6% by mass.

[0070] [sweet potato]

[0071] The sweet potatoes cultivated using the cultivation method of this embodiment can include a variety of varieties with different skin colors, flesh colors, and flavors, and are not particularly limited. Furthermore, in addition to the above, sweet potatoes for processing and sweet potatoes for starch production can also be used in the same way.

[0072] [Cultivation Methods]

[0073] There are no particular restrictions on the cultivation methods of sweet potatoes, such as seed potato cultivation and cutting cultivation, but cutting cultivation is preferred.

[0074] As an example, the following methods can be listed in the case of propagation by cuttings.

[0075] Sweet potatoes are a robust crop that is relatively tolerant of high temperatures and dryness, and can grow well even in poor soil. However, it is best to transplant cuttings into temperate to subtropical fields with an average temperature of 20–35℃ and moderate humidity, around May to June. Cuttings can be obtained using existing methods. The preferred cultivation environment is a sunny, well-aerated, relatively dry field with sufficient nutrients (especially nitrogen). The field should ideally be deeply plowed and ridged beforehand. Drainage is crucial in sweet potato cultivation, so the ridge height should ideally be 20–30 cm. The ridge width should ideally be 50–100 cm, and the ridge spacing should ideally be around 50–100 cm. Cuttings of about 20–40 cm are planted with a spacing of about 20–50 cm, a depth of about 5–20 cm, and the leaves exposed above the ground, and then gently pressed down. Planting methods include vertical planting, inclined planting, and horizontal planting, among others, without particular restrictions. After planting, roots will develop in about one week. From planting to harvest, management such as fertilization, hilling, and watering should preferably be carried out according to conventional farming methods. The plants should be pulled up 120 to 150 days after planting, and the tubers at the base should be harvested.

[0076] The sweet potato cultivation method of this embodiment includes applying the plant stimulant to the seedlings. In this specification, "seedling" of sweet potato, in the case of seed potato cultivation, refers to seedlings within 30 days after the sprouted seed potatoes are transplanted into the field; in the case of cutting cultivation, it refers to cuttings collected from seed potatoes and seedlings within 30 days after the cuttings are transplanted into the field.

[0077] In one embodiment, in the cultivation of cuttings, it is preferable to apply the plant stimulant at least once to seedlings 2 to 30 days after transplanting. More preferably, the plant stimulant is applied at least once to seedlings 2 to 20 days after transplanting; even more preferably, it is applied at least once to seedlings 2 to 10 days after transplanting; and even more preferably, it is applied once each to seedlings 2 to 10 days and 15 to 30 days after transplanting. To obtain more robust seedlings, it is particularly preferable to soak the cut surfaces of the cuttings before transplanting in the plant stimulant for 5 to 48 hours. Furthermore, it is even more preferable to apply the plant stimulant at least once to seedlings 2 to 30 days after transplanting, and then apply it to the remaining plants at least once every 10 to 20 days.

[0078] As another embodiment of the sweet potato cultivation method of this invention, it is preferable to further apply the plant stimulant to the plants after the seedling stage. In this specification, "plants after the seedling stage" refers to plants that have passed through the aforementioned "seedling" period, that is, plants 30 days or more after transplanting.

[0079] In one embodiment, it is preferable to apply the plant stimulant at least once to the plants after the seedling stage. More preferably, it is applied approximately 90 days after transplanting, at a rate of once every 10 to 20 days.

[0080] (Application of plant stimulants)

[0081] The application of plant stimulants to sweet potatoes can be carried out using methods customary in the industry. There are no particular limitations on the dispersal method; for example, it can be done by direct dispersal to the leaves and stems of the plant, dispersal in the culture medium or soil, or dispersal in the culture medium or soil after mixing with fertilizers. As a dispersal method, foliar dispersal is preferred, especially for effectively expressing the activity of the elicitors. Foliar dispersal can be carried out using methods customary in the industry, such as powered sprayers, shoulder-mounted sprayers, spreaders, sprayers, manned or unmanned helicopters, foggers, and manual sprayers.

[0082] The preferred distribution of plant stimulants is that the active ingredient is distributed per 1 cm³. 2 The amount of active ingredient distributed on the leaf surface is 0.1 ng to 100 ng, more preferably 0.1 ng to 100 ng per 1 cm². 2 The amount dispersed on the leaf surface is 1 ng to 20 ng. In actual field conditions, since it is difficult to selectively disperse the substance on the leaf surface and ensure that all dispersed substances adhere to the leaf surface, it is preferable to dilute it to a concentration of 1 ppm to 100 ppm by mass, distributing it per 100 m². 2The active ingredient, ranging from 0.01 g to 20 g per cultivated area, is evenly distributed from above the plant. More preferably, it is diluted to a concentration of 10 ppm to 500 ppm by mass, as in the plant stimulant, and distributed per 100 m². 2 The active ingredients, ranging from 0.1g to 10g per cultivated area, are evenly distributed from the top of the plant.

[0083] In the sweet potato cultivation method of this embodiment, soil management is preferably carried out through conventional tillage methods.

[0084] (Effects of plant-based stimulants)

[0085] The sweet potato cultivation method of this embodiment includes applying a plant stimulant containing exogenous and endogenous elicitors to sweet potato seedlings. Furthermore, it is preferable to continue applying the plant stimulant containing exogenous and endogenous elicitors to the plant after the seedling stage. The rationale for the effectiveness of applying such a plant stimulant at this stage is not fully explained. It can be considered that by applying exogenous elicitors (e.g., derived from chitin oligosaccharides), the plant can be endowed with resistance to diseases derived from herbivores, but excessive application can lead to growth inhibition. On the other hand, by applying endogenous elicitors (e.g., derived from cellulose oligosaccharides or xylooligosaccharides), the plant can recognize its own cell damage and fragmentation components (DAMPs: damage-associated molecular patterns), and it is expected to promote its own growth for the acquisition of immunity and cell repair. It can be considered that in the sweet potato cultivation method of this embodiment, in particular, by applying a plant stimulant containing exogenous and endogenous elicitors during the early seedling stage, strong seedlings capable of suppressing growth inhibition and conferring disease resistance can be cultivated. It can be considered that by continuing to apply the plant stimulant to such strong plants, the growth-promoting effect of the endogenous elicitors will not be strongly inhibited by the exogenous elicitors, thus achieving a high developmental effect through the complementary effects of the two. Therefore, it can be presumed that when cultivating sweet potatoes, by applying the plant stimulant to the seedlings after transplanting at least once, and preferably to the seedlings before transplanting, the rooting of adventitious roots (roots that swell to become tubers) is strongly promoted. Furthermore, by applying the plant stimulant to the plants after the seedling stage at least once, the plants grow vigorously, promoting the enlargement of adventitious roots and increasing the yield.

[0086] The present invention is further illustrated by the following embodiments, but the present invention is not limited thereto.

[0087] Example

[0088] [1. Preparation of oligosaccharides]

[0089] (1) Chitin oligosaccharides

[0090] 10g of chitin powder (Wako Pure Chemical Industries, purified chitin) was dispersed in 30mL of water containing 1.2g of 85% phosphoric acid (Wako Pure Chemical Industries, premium grade reagent), and dried under reduced pressure. The resulting powder was then added together with 100g of alumina balls with a diameter of 5mm into a 250mL alumina container and placed in a planetary ball mill. The reaction product was obtained by continuously treating with PULVERISETTE 6 at 500 rpm for 6 hours. Regarding temperature, the reaction started at room temperature, and the temperature rise due to shear heating proceeded naturally.

[0091] The reaction product was then suspended in water and neutralized with calcium hydroxide. The resulting slurry was filtered through a suction filter using 5B filter paper. The recovered filtrate was freeze-dried to obtain chitin oligosaccharide powder.

[0092] (2) Fiber oligosaccharides

[0093] Use a food mixer (model: HBF500S). Cottonseed pulp (Chinese origin, 97% cellulose content) 271g (moisture content 1.8%, dry weight 266g) was mixed with 85% phosphoric acid ( 38g of a special grade reagent manufactured by the company was mixed to obtain 309g of reaction raw materials (moisture content 3.4%, phosphoric acid content 10.4%).

[0094] Next, 309g of the reaction raw materials were mixed with... 13 kg of 3 / 4-inch carbon steel balls were fed into a vibratory mill (model MB-1, manufactured by Chuo Kagaki Co., Ltd., tank size 5L). After 24 hours of dry pulverization hydrolysis under the conditions of total amplitude 8 mm, frequency 16.2 Hz, and jacket water temperature 75°C, the reaction powder was recovered.

[0095] 10g of the reaction powder and 90g of ion-exchanged water were added to a 200L beaker and stirred at 25°C for 1 hour using an electromagnetic stirrer to obtain an extract of cellulose hydrolysate.

[0096] Next, 1.3 g of 40% calcium hydroxide aqueous solution was added to the extract, and the mixture was stirred at 25°C for 1 hour using an electromagnetic stirrer. After the supernatant was recovered from the prepared neutralized liquid by centrifugation, it was freeze-dried to obtain cellulose oligosaccharide powder.

[0097] (3) Xylo-oligosaccharides

[0098] The TN strain of *Acremonium cellulolyticus* (FERM P-18508) was cultured in a liquid medium containing: Avicel (microcrystalline cellulose) 50 g / L, KH₂O₄ 24 g / L, ammonium sulfate 5 g / L, potassium tartrate 1 / 2H₂O 4.7 g / L, urea 4 g / L, Tween 80 1 g / L, and MgSO₄. 7H2O 1.2g / L, ZnSO4 7H2O 10mg / L, MnSO4 5H₂O 10mg / L, CuSO₄ The xylooligosaccharide raw material powder was cultured in a 500 mL flask containing 100 mL of 5H₂O (10 mg / L) at 30 °C with shaking for 6 days. 5 g of corn cob powder was suspended in 50 mL of the supernatant obtained from centrifugation of the culture medium, and the mixture was stirred at 50 °C for 72 hours. The supernatant from centrifugation of the resulting reaction solution was freeze-dried to obtain xylooligosaccharide raw material powder.

[0099] [2. Sweet potato cultivation]

[0100] (1) Preparation of plant stimulants

[0101] The oligosaccharides prepared in [1. Preparation of Oligosaccharides] were dissolved in water by stirring with a stirrer at each composition ratio, with the concentration (mass ppm) of the active ingredient in the plant stimulants shown in Examples 1-11 and Comparative Examples 1-5 in Table 1 being 1000 times higher. The solution was then sterilized using a 0.45 μm filter, and the resulting liquid was used as the plant stimulant stock solution. This stock solution was diluted 1000 times with water and used in the following cultivation experiments. Hereinafter, the plant stimulant obtained by diluting the stock solution 1000 times is sometimes referred to as "plant stimulant diluted solution". Furthermore, the composition ratios of each oligosaccharide in the table represent mass%.

[0102] (2) Cultivation Experiment 1 (Examples 1-25, Comparative Examples 1-11)

[0103] Sweet potato cultivation was carried out in fields within plastic greenhouses. Two weeks before the planned planting time, the fields were tilled to create ridges 80cm wide, 80cm apart, and 25cm high. Sweet potato cuttings (approximately 30cm long) were planted at 30cm intervals and a depth of 10-12cm using a slanted planting method. The cuttings were gently pressed down, thoroughly watered, and established after 5-7 days. The cuttings were then divided into 27 sections of 5 plants each and cultivated using conventional methods.

[0104] For seedlings (cuttings) before transplanting, seedlings after transplanting, and plants after the seedling stage, the plant stimulant diluted solution was soaked under the conditions recorded in Tables 1-3, or dispersed to the extent that the leaves and soil were moistened.

[0105] The pre-planting immersion treatment of cuttings was performed by immersing the cut ends of the cuttings in a diluted plant stimulant solution placed in a container for 24 hours. For the dispersal treatment of seedlings after transplanting and plants after the seedling stage, the diluted plant stimulant solution was prepared at 1 kg / zone / time, and dispersal was performed by foliar application using a spray bottle and irrigation of the soil near the roots, as described in Table 1. Harvesting was carried out 140 days after transplanting, and the average yield per zone (5 plants) was measured and compared under various conditions.

[0106] In addition, the yield was determined by cutting the tubers (edible portion) from the root of the plant and measuring the average weight of the standard portion (2S-3L) of tubers per plant. The experimental results are shown in Tables 1-3.

[0107]

[0108] The results in Tables 1-3 confirm that in sweet potato cultivation, the yield is significantly increased when plant stimulants containing both exogenous and endogenous elicitors are used on seedlings. Although not shown in the data, a tendency to increase tubers of M-2L size was observed, particularly when applied to seedlings after transplanting. The reason for this is unclear, but it is presumed that 1-3 applications within 30 days after transplanting promote adventitious rooting and growth. Furthermore, while using only one endogenous elicitor in addition to the exogenous elicitor can achieve sufficient effects, the combined use of two endogenous elicitors yielded even greater results.

Claims

1. Sweet potato cultivation methods, including: Apply a plant stimulant containing exogenous and endogenous elicitors to the seedlings at least once.

2. The sweet potato cultivation method according to claim 1, comprising: The plant stimulant is soaked in the cut of the cuttings collected from seed potatoes for 5 to 48 hours.

3. The method for cultivating sweet potatoes according to claim 1 or 2, comprising: Apply the plant stimulant at least once to seedlings within 30 days of transplanting sprouted seed potatoes into the field, or to seedlings within 30 days of transplanting cuttings collected from seed potatoes into the field.

4. The method for cultivating sweet potatoes according to claim 1 or 2, comprising: Further, apply the plant stimulant at least once to the plant after the seedling stage.

5. The sweet potato cultivation method according to claim 1 or 2, wherein the exogenous elicitor is a chitinous oligosaccharide, and the endogenous elicitor is selected from at least one oligosaccharide among cellulosic oligosaccharides and xylooligosaccharides.

6. The sweet potato cultivation method 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.

7. The method for cultivating sweet potatoes according to claim 1 or 2, wherein the endogenous elicitor comprises xylooligosaccharides.

8. The sweet potato cultivation method according to claim 7, wherein the endogenous elicitor comprises both cellulosic sugar and xylooligosic sugar.

9. The sweet potato cultivation method according to claim 8, wherein the mass ratio of the fiber oligosaccharide to the xylooligosaccharide in the plant stimulant is 0.2 to 5.

10. The sweet potato cultivation method according to claim 1 or 2, wherein the plant stimulant is applied to the plant at a concentration of 0.1 to 500 ppm by mass of the total content of the exogenous elicitor and the endogenous elicitor.

11. The method for cultivating sweet potatoes according to claim 1 or 3, wherein the plant stimulant is applied to the plant through foliar dissemination.

12. The cultivation method of sweet potato involves using plant stimulants containing exogenous and endogenous elicitors in the cultivation of seed sweet potatoes. include: The seedlings are treated with the plant stimulant at least once, wherein the exogenous elicitor of the plant stimulant is a chitinous oligosaccharide and the endogenous elicitor is at least one oligosaccharide selected from cellulose oligosaccharides and xylooligosaccharides.

13. A plant stimulant is a plant stimulant containing exogenous and endogenous elicitors used in the cultivation of sweet potatoes, applied to seedlings at least once.

14. The plant stimulant according to claim 13, applied to cuttings prior to transplanting.

15. The plant stimulant according to claim 13 or 14, applied at least once to seedlings within 30 days after the sprouted seed potatoes are transplanted into the field, or to seedlings within 30 days after the cuttings collected from seed potatoes are transplanted into the field.

16. The plant stimulant according to claim 13 or 14, further applied to the plant body at least once after the seedling stage.

17. The plant stimulant according to claim 13 or 14, wherein the exogenous elicitor is a chitinous oligosaccharide, and the endogenous elicitor is at least one oligosaccharide selected from cellulose oligosaccharides and xylooligosaccharides.

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.

19. The plant stimulant according to claim 13 or 14, wherein the endogenous elicitor comprises xylooligosaccharide.

20. The plant stimulant according to claim 19, wherein the endogenous elicitor comprises both cellulosic acid oligosaccharide and xylooligosaccharide.

21. The plant stimulant according to claim 20, wherein the mass ratio of the cellulose oligosaccharide to the xylooligosaccharide in the plant stimulant is 0.2 to 5.

22. The plant stimulant according to claim 13 or 14, applied to plants at a concentration of 0.1 to 500 ppm by mass of the total content of the exogenous elicitor and the endogenous elicitor.

23. The plant stimulant according to claim 13 or 14, applied to plants by foliar dispersal.

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