Use of phlorotannins as stimulants of mycorrhizal and rhizobian symbioses

Abstract

The invention relates to the use of phlorotannins, in particular extracts from brown algae of the Fucaceae family, especially from the genera Fucus or Ascophyllum, to stimulate symbiosis between a plant and a mycorrhizal fungus or rhizobium. The invention also relates to a fertilizer product containing phlorotannins and its use in a plant treatment method.

Description

Use of phlorotannins as stimulants of mycorrhizal and rhizobian symbioses The present invention, applicable in the agricultural field, essentially relates to the use of phlorotannins, in particular extracted from brown algae, especially from the Fucaceae family, and more specifically from the genera Fucus or Ascophyllum, to stimulate symbiosis between a plant and a mycorrhizal fungus. Phlorotannins are a type of tannin found in the cell walls of brown algae. These compounds are oligomers of phloroglucinol. The present invention also relates to a method for stimulating symbiosis between a plant and a mycorrhizal fungus by applying to said plant or to the soils an effective amount of phlorotannins, in particular extracts of brown algae of the Fucaceae family. For the purposes of this description, the expression "fertilizer composition" is intended to designate any product whose use is intended to guarantee or improve the physical, chemical or biological properties of soils, as well as the nutrition of plants. This composition could be, for example, a fertilizer applied through the roots. Fertilizers are known to be defined as fertilizing substances whose main function is to provide plants with the elements directly useful for their nutrition (main fertilizing elements, secondary fertilizing elements and trace elements). For this purpose, root fertilizers generally use sources of nitrogen, phosphorus and potassium, as well as trace elements and amino acids. Plants are known to develop symbiotic relationships with microorganisms, allowing them to efficiently acquire nutrients. Among the most economical and ecologically sound symbiotic relationships are those between plants and mycorrhizal fungi, or between legumes and nitrogen-fixing bacteria known as rhizobia. The document by Dhiriti Battachar and Ya et al. ("Seaweed extracts as biostimulants in horticulture", Scientia Horticulturae, September 2015) describes the use of seaweed extracts, for example, from brown algae (such as A. nodosum, Tables 1, 2, and 3), as biostimulants in horticulture. No reference is made to phlorotannins or to the symbiosis between a plant and a mycorrhizal fungus. The document Dong-Kyung Yu et al. ("Phlorofucofuroeckol B suppresses inflammatory responses by down-regulating nuclear factor [kappa]B activation via Akt, ERK, and JNK in LPS-stimulated microglial cells", International Immunology, October 2020) describes the anti-inflammatory properties of florofucofuroeckol B (PFF-B) isolated from a brown alga (Ecklonia stolonifera). No reference is made to phlorotannins or to the symbiosis between a plant and a mycorrhizal fungus. The document by Katarzyna Chojnacka et al. ("Biologically Active Compounds in Seaweed Extracts - the Prospects for Application", The Open Conference Proceedings Journal, August 2012) describes compounds present in seaweed extracts, such as phlorotannins. At no point is any reference made to the symbiosis between a plant and a mycorrhizal fungus. The document Yliopistin Turun et al. ("Brown algal phlorotannins improving and applying chemical methods", 2008) describes the various biological properties of phlorotannins for brown algae. At no point is reference made to the symbiosis between a plant and a mycorrhizal fungus. The document Yong-Xin Li et al. ("Phlorotannins as bioactive agents from brown algae", Process Biochemistry, Elsevier, September 2011) describes the medicinal properties of phlorotannins present in brown algae, in particular the bactericidal activity of phlorotannins. The document Wajahatullah Khan et al. ("Commercial Extract of Ascophyllum nodosum Improves Root Colonization of Alfalfa by its Bacterial Symbiont Sinorhizobium meliloti", Communications in Soil Science and Plant Analysis, October 2012) describes the effect of an extract of brown seaweed (A. nodosum) on the colonization of alfalfa roots by the bacterium S. meliloti. No reference is made to phlorotannins or to the symbiosis between a plant and a mycorrhizal fungus. The document Wajahatullah Khan et al. ("Seaweed Extracts as Biostimulants of Plant Growth and Development", Journal of Plant Growth Regulation, May 2009) describes the biostimulant properties of seaweed extracts on plant growth, including the effect of alginates on fungal growth. The paper by James S. Craigie ("Seaweed extract stimuli in plant science and agriculture," Journal of Applied Phycology, Kluwer Academic Publishers, DO, July 2010) analyzes the properties of seaweed extracts (e.g., A. nodosum) in agriculture. The paper specifically describes the use of seaweed extracts as a fertilizer. No reference is made to the symbiosis between a plant and a mycorrhizal fungus. The document R. Sathya et al. ("Antioxidant properties of phlorotannins from brown seaweed Cystoseira trinodis (Forsskal) C. Agardh", Arabian Journal of Chemistry, October 2013) describes the antioxidant properties of phlorotannins obtained from brown seaweed (Cystoseira trinodis). Plant-mycorrhizal fungi symbiosis Mycorrhizal fungi are capable of forming a close symbiosis with plant roots. They are associated with more than 90% of plant species, such as cereals, grasses, potatoes, corn, sunflowers, cotton, coffee, fruit trees, sugarcane, legumes, and ornamental plants. This symbiosis does not occur in some species, such as rapeseed, cabbage, and sugar beets. The result of the symbiotic association between a mycorrhizal fungus and a plant root is called a mycorrhiza. Mycorrhizal fungi colonize the plant's root system. They are considered extensions of the plant's roots. This network of filaments connected to the plant's roots acts like telescopic arms, extracting nutrients from the soil. This network allows the plant to increase its root exploration capacity, thus giving it access to nutrients inaccessible through the root system. The symbiosis between plants and mycorrhizal fungi leads to improved fertilizer efficiency and reduced losses due to leaching or erosion. In return, the plant provides the mycorrhizal fungi with the sugars necessary for their growth and for the synthesis of glomalin by the mycorrhizal filament network. Glomalin is a glycoprotein excreted by the filament network that contributes to soil structuring and improves its organic matter content. In fact, through the production of glomalin, mycorrhizal fungi facilitate phytostabilization by creating a natural barrier that induces resistance to erosion and leaching. They can also be used to minimize soil contamination by metals. The agronomic effects associated with stimulating symbiosis between a plant and a mycorrhizal fungus are numerous. In particular, stimulating this symbiosis allows for: - optimize fertilizer efficiency - Improve accessibility to relatively immobile fertilizer elements, such as phosphorus - to stimulate plant growth, flowering and / or fruiting - improve crop yield and quality - improve soil salinity tolerance - Improve resilience to climate stress, particularly drought and heat stress - reduce the sensitivity of crops to pathogens and nematodes - reduce losses due to leaching and erosion - improve soil structure. The degree of mycorrhization in a crop appears to be a factor that influences the yield and quality of agricultural products, with repercussions for environmental protection. The degree of mycorrhization is determined by observing the color of the roots and counting the points where hyphae are present, or by counting the number of spores or clusters. Currently, particularly low levels of mycorrhization are observed in soils due to various agricultural practices, such as the massive use of fertilizers and pesticides, monoculture, lack of crop rotation, the development of non-mycorrhizal crops (rapeseed, sugar beet, cabbage, etc.) or intensive tillage techniques. Legume-rhizobium symbiosis Rhizobia (genus Rhizobium) are aerobic soil bacteria belonging to the family Rhizobiaceae. The symbiosis between a leguminous plant and a rhizobium is an essential process for the plant to obtain nitrogen in a reduced form, and also for the rhizobia to obtain the nutrients necessary for their development. The leguminous plant provides nutrients to the rhizobium, which captures nitrogen from the air and transfers it to the host. This symbiosis leads to the formation of new organs called root nodules. Root nodules are small protuberances that form on the roots under the action of the rhizobia. These root nodules harbor endosymbiotic rhizobia from the cells of the leguminous plant, which reduce atmospheric nitrogen to ammonium. This reduced nitrogen is transferred to the plant and used for its growth.Symbiotic nitrogen fixation significantly improves nitrogen availability to the plant. The importance of these rhizobia is therefore considerable, as they can fix up to 350 kg / ha / year of nitrogen. Similar to the symbiosis between a plant and a mycorrhizal fungus, cultivation practices can also affect the formation of the symbiosis between a legume and a rhizobium. This can lead to a decrease in root nodule formation. Therefore, there is a great need for new fertilizer products that can remedy plant deficiencies, particularly by stimulating symbiosis between a plant and a mycorrhizal fungus, as well as symbiosis between a leguminous plant and a rhizobium. Seaweed is an abundant plant resource and has long been used as a soil fertilizer in coastal regions. Treating various plants with seaweed extracts has been shown to promote seed germination, increase yields, improve disease resistance, and extend fruit shelf life. These findings regarding plant growth and health have been attributed primarily to the richness of the seaweed used in betaines, phytohormones, polysaccharides, and trace elements. In this context, the applicant has demonstrated, and this forms the basis of the present invention, that phlorotannins, particularly those extracted from brown algae of the Fucaceae family, surprisingly and unexpectedly stimulate mycorrhizal and rhizobian symbioses. This intense activity is further supported by the stimulation of sporulation and nodulation. Therefore, these phlorotannins can be used as a supplement in fertilizer compositions, such as fertilizers, as activators of spore and nodule formation. These compositions allow for increased absorption of nutrients from the soil and improved plant health, meeting the crop's growth needs, which will result, in particular, in higher yields and better harvest quality. These compositions also allow for improved fertilization efficiency and reduced losses due to leaching and erosion problems. Thus, according to a first aspect, the present application is intended to cover the use of phlorotannins, in particular extracted from brown algae of the Fucaceae family, to stimulate symbiosis between a plant and a mycorrhizal fungus. The useful phlorotannins according to the invention are polyphenols present specifically in the cell walls and cells of brown algae of the Fucaceae family. Phlorotannins represent between 5 and 200 mg / g of the dry weight of the algae. In one particular embodiment, the plant is a legume. Legumes belong to the Fabaceae family. Legumes play an important role in the food sector due to their high protein and essential amino acid content. Non-exhaustive examples of legumes include soybeans, peanuts, beans, peas, lentils, chickpeas, broad beans, kidney beans, vetch, forage peas, alfalfa, clover, lupins, mung beans (germinated soybean sprouts), licorice, rosewood, horned clover, sainfoin, rooibos, and fenugreek. In one particular embodiment, phlorotannins also enable the stimulation of symbiosis between a leguminous plant and a rhizobium. Preferably, this stimulation of symbiosis between a leguminous plant and a rhizobium is combined with the stimulation of symbiosis with a mycorrhizal fungus. This application also aims to cover the use of phlorotannins, in particular extracted from brown algae of the Fucaceae family, to stimulate symbiosis between a leguminous plant and a rhizobium. Advantageously, the phlorotannins used according to the present invention are extracts of algae selected from the group consisting of species of the genera Fucus and Ascophyllum, in particular from the group consisting of the species Fucus vesiculosus, Fucus serratus and Ascophyllum nodosum. Phlorotannin-rich seaweed extracts suitable for use in the context of the present invention can be obtained from the aforementioned seaweed species by a process that generally comprises the following steps: washing, crushing, extraction (solid-liquid separation) and, optionally, fractionation and concentration. The resulting extract can be more or less concentrated depending on its intended use. Complete dehydration of this extract, which allows for presentation as a water-soluble powder, can be achieved, for example, using a drum dryer or spray drying. The extraction conditions and the type of algae will be selected so that the resulting extract has the desired concentration for the intended application. These selections can be easily made by experts in the field, particularly taking into account the general guidelines set out below. Generally, the amount of phlorotannins supplied to plants ranges from 10 to 1000 g / ha, and is preferably around 100 g / ha, for applications in solid form in powder or granulated fertilizers. In one particular embodiment, phlorotannins further enable the plant to stimulate the uptake of one or more elements selected from nitrogen, phosphorus, potassium, and calcium. For the purposes of the present invention, "stimulating uptake" means a significant increase in uptake and / or an improvement in the uptake mechanisms. Thus, in one particular embodiment, phlorotannins also enable the plant to stimulate the uptake mechanisms of one or more elements selected from nitrogen, phosphorus, potassium, and calcium. In the context of the present invention, an effective amount of phlorotannin is supplied to the plant to stimulate the uptake of one or more elements selected from nitrogen, phosphorus, potassium, and calcium.Thus, in a particular embodiment, the phlorotannins are supplied to the plant in an amount effective to increase the plant's uptake of one or more of the aforementioned elements by at least 5%, for example, at least 10%, at least 15%, at least 20%, at least 25%, at least 30%, at least 40%, for example, at least 50%. In other words, the phlorotannins supplied to the plant allow the plant's content of one or more of the aforementioned elements to be increased by at least 5%, for example, at least 10%, at least 15%, at least 20%, at least 25%, at least 30%, at least 40%, for example, at least 50%. The increase in uptake is measured by determining the nitrogen, phosphorus, potassium, and / or calcium content in the plant. The term "increase" refers to the plant before phlorotannin application, for example, compared to a plant that has not received any phlorotannin application. The nitrogen, phosphorus, potassium, and / or calcium content is expressed as weight / dry matter weight, which corresponds to the mass of nitrogen, phosphorus, potassium, and / or calcium contained in a dry plant sample. The measurement of nitrogen, phosphorus, potassium, and / or calcium content is performed using a suitable analytical procedure. The present invention also aims to protect the use of phlorotannins, particularly those extracted from brown algae of the Fucaceae family, to stimulate the uptake by a plant of one or more elements selected from nitrogen, phosphorus, potassium, and calcium. In one particular embodiment, the phlorotannins are supplied to the plant in an amount effective in increasing the plant's uptake of one or more of the aforementioned elements by at least 5%, for example, at least 10%, at least 15%, at least 20%, at least 25%, at least 30%, at least 40%, or, for example, at least 50%. In other words, the phlorotannins supplied to the plant allow the content in the plant of one or more of the elements mentioned to be increased by at least 5%, for example, by at least 10%, at least 15%, at least 20%, at least 25%, at least 30%, at least 40%, for example, at least 50%. According to a second aspect, the present application aims to protect a procedure for stimulating symbiosis between a plant and a mycorrhizal fungus, characterized in that it comprises the application to said plant or to the soil of an effective amount of phlorotannins, in particular extracted from brown algae of the Fucaceae family. In one particular embodiment, the plant is a legume. Thus, the process according to the present invention also allows for the stimulation of symbiosis between a legume and a rhizobium. Preferably, the stimulation of symbiosis between a legume and a rhizobium is combined with the stimulation of symbiosis with a mycorrhizal fungus. The present application also aims to cover a process for stimulating symbiosis between a legume and a rhizobium, characterized in that it comprises the application to said plant or to the soil of an effective quantity of phlorotannins, in particular extracted from brown algae of the Fucaceae family. Advantageously, the application to plants is done via the root system. The effective amount of phlorotannins supplied to plants is 0.1 to 100 g per liter, and preferably around 5 g per liter, for liquid applications in root nutrient solutions (hydroponics, drip irrigation, etc.), or 10 to 1000 g / ha, and preferably around 100 g / ha, for solid applications in powder or granulated fertilizers. In one particular embodiment, phlorotannins also allow the stimulation of the plant's absorption of one or more selected elements from among nitrogen, phosphorus, potassium, and calcium. The present invention also aims to protect a process for stimulating the absorption by a plant of one or more elements selected from nitrogen, phosphorus, potassium and calcium, characterized in that it comprises the application to said plant or to the soil of an effective amount of phlorotannins, in particular extracted from brown algae of the Fucaceae family. In one particular embodiment, phlorotannins are applied to the plant or soil in an amount effective to increase the plant's uptake of one or more of the aforementioned elements by at least 5%, for example, at least 10%, at least 15%, at least 20%, at least 25%, at least 30%, at least 40%, for example, at least 50%. In other words, the phlorotannins applied to the plant or soil allow the content of one or more of the aforementioned elements in the plant to increase by at least 5%, for example, at least 10%, at least 15%, at least 20%, at least 25%, at least 30%, at least 40%, for example, at least 50%. This description also describes, although it is not included within the scope of protection, a fertilizer product characterized by containing an effective amount of phlorotannins, in particular L extracted from brown algae of the Fucaceae family, optionally in combination with one or more fertilizer substances. Advantageously, the fertilizer product is characterized by being: - either in liquid form and containing an amount of phlorotannins of 0.1 to 100 g per liter, and preferably on the order of 5 g per liter; - either in solid form, particularly in powder or granule form, and because it contains an amount of phlorotannins that allows an input of 10 to 1000 g, preferably on the order of 100 g per hectare. The fertilizer product, which is not included in the scope of protection, may be presented in different forms, such as: - an amendment, in particular a calcareous amendment or an organic amendment; - a fertilizer, in particular a root fertilizer; - a nutrient solution, in particular a root nutrient solution. The fertilizer product may contain an effective amount of phlorotannins, particularly those extracted from brown algae of the Fucaceae family, in combination with one or more fertilizer substances. The fertilizer substance may be a source of calcium, in particular calcium carbonate, calcium sulfate, gypsum, and / or phosphogypsum. The combination of phlorotannins and the calcium source, particularly calcium carbonate, allows for optimal stimulation of the symbiosis between the plant and the mycorrhizal fungus. Examples of fertilizer products not included in the scope of protection include calcareous amendments, organic amendments and growing substrates, root fertilizers of the NP, PK, NPK type, etc., or even root nutrient solutions. Fertilizing substances that can be used in combination with phlorotannins can be of various types and can be selected, for example, from urea, ammonium sulfate, ammonium nitrate, natural phosphate, potassium chloride, magnesium nitrate, manganese nitrate, zinc nitrate, copper nitrate, phosphoric acid, and boric acid. The present invention finds application in the treatment of a wide variety of plants. Among them, the following should be mentioned in particular: - extensive crops, such as cereals (wheat, corn, sugar cane, etc.), - protein-rich vegetables (peas), - oilseeds (soybeans, sunflowers), - the vine, - meadow plants useful for animal feed, - specialized crops such as, in particular, horticulture (lettuce, spinach, tomato, melon), vines, arboriculture (orange trees, pear trees, apple trees, nectarines) or horticulture (rose bushes). In this application, the term "plant" refers to the plant considered as a whole, including its root system, vegetative system, seeds and fruit. The present invention will be illustrated below by the following non-limiting examples. In these examples, and unless otherwise stated, percentages are expressed by weight and temperature is room temperature. EXAMPLE 1 - Procedure for preparing phlorotannins usable within the scope of the invention A - General description a) Preparation of a phlorotannin extract from Ascophyllum nodosum The phlorotannin fraction was obtained by aqueous extraction from fresh algae (200 g of Ascophyllum nodosum per liter of water). The extraction consisted of an acid hydrolysis (pH 3) carried out under stirring for 48 h, with 1 h of heating at 90-100 °C. The extract was then filtered through a membrane (porosity of 80 µm). b) Preparation of a phlorotannin extract from Fucus vesiculosus The phlorotannin fraction was obtained by aqueous extraction from fresh algae (200 g of Fucus vesiculosus per liter of water). The extraction consisted of acid hydrolysis (pH 3) carried out under stirring for 48 h at room temperature. The extract was then filtered through a membrane (80 µm porosity). The solvent (water) was evaporated to obtain a water-soluble powder. B - Detailed example of the preparation of a phlorotannin extract: A phlorotannin extract was obtained following the following experimental protocol: a) Washing Fresh algae of the Ascophyllum nodosum or Fucus vesiculosus type were subjected to two successive washes in a water tank to remove sand and gravel. b) Crushing The washed algae were drained and then crushed into pieces of 1 to 10 mm. c) Extraction 200 kg of algae were dispersed in a heated reactor containing 1000 kg of an aqueous solution maintained at room temperature (Fucus vesiculosus) or heated to 90 °C (Ascophyllum nodosum). The mixture was kept under agitation for approximately 48 hours and 2 hours, respectively. Prior to extraction, the already crushed algae cells underwent microfracturing using an ULTRA-TURAX® homogenizer to facilitate extraction. The separation operation is carried out at the end of the extraction stages. d) Separation The soluble fraction rich in phlorotannins was separated from the algae remains by centrifugation (solid-liquid separation). The centrifuged extract was then filtered using a diatomaceous earth filter or a plate filter, and subsequently filtered again through a membrane down to 1 µm. The filtrate thus obtained contains between 0.1 and 10% by weight of dry extract. The extract thus prepared can be used in a more or less concentrated form, the final concentration being determined according to the desired content of active derivatives in the intended application. Thus, the filtrate mentioned above can be concentrated, for example, by means of a downflow evaporator, so that the dry extract represents between 10 and 60% by weight of the same. Total dehydration can also be achieved, for example, by using a drum dryer or by spray drying when a presentation in the form of a water-soluble powder is desired. Following the procedure described above, various phlorotannin extracts were prepared from two species of brown algae from the genera Ascophyllum and Fucus. The composition of these dried phlorotannin extracts is shown in Table 1 below. TABLE 1: Composition of phlorotannin extracts from ardas EXAMPLE 2 - Effects of a phlorotannin extract on the sporulation of Rhizophaqus intraradices and on biomass production in maize Pre-germinated maize seeds were sown in 0.9 m³ pots at a ratio of one seed per pot. The pots had been previously filled with a culture medium inoculated with the mycorrhizal fungus Rhizophagus intraradices. The plants were grown for 8 weeks under controlled conditions. The control group was watered 3 times a week with reverse osmosis water, while the treated group was watered with reverse osmosis water for the first week and, thereafter, with the phlorotannin extract prepared according to Example 1 diluted in water (at a ratio of 100 g / ha of phlorotannins). Both the control and treated groups were watered with reverse osmosis water during the first week. From the second week onward, the reverse osmosis water was replaced with the phlorotannin extract.Fertilizer application began in the third week using a 15 / 3 / 25 fertilizer, corresponding to the nitrogen / phosphorus / potassium content, respectively, applied weekly in the irrigation water. Two phlorotannin extracts were tested: one derived from Ascophyllum nodosum (AN extract) and the other from Fucus vesiculosus (FV extract). Rhizophagus intraradices sporulation controls were carried out after 6 and 8 weeks of cultivation. For each control, 5 plants per group were analyzed. Fungal material was extracted from each plant. Spore clusters were counted using a binocular microscope. In the case of the FV extract, measurements of the aboveground and root biomass of the corn plants were taken after 8 weeks of cultivation. Five plants per group were analyzed. The two phlorotannin extracts have a significant effect on the number of spore clusters and the number of spores per cluster of Rhizophagus intraradices. Application of the FV extract also increases the fresh matter content of the aerial and root parts of corn plants. TABLE 2: Ef 2 xr fl r nin rlnmrr im r Rhiz h inr ri The results presented in Table 2 show a marked increase in the average number of spore clusters in plants treated with phlorotannins, compared to control plants. TABLE 3: Effect of a phlorotannin extract derived from Fucus vesiculosus on the number of spores per cluster Rhiz h inr ri The results presented in Table 3 show an increase in the number of clusters with more than 10 spores in plants treated with phlorotannins derived from Fucus vesiculosus, compared to control plants. TABLE 4: Effect of a phlorotannin extract derived from Ascophyllum nodosum on the number of spores per r im Rhiz h inr ri The results presented in Table 4 show an increase in the number of clusters with more than 10 spores in plants treated with phlorotannins derived from Ascophyllum nodosum, compared to control plants. TABLE 5: Effect of a phlorotannin extract derived from Fucus vesiculosus on the growth of maize plants The results presented in Table 5 show that plants treated with phlorotannins derived from Fucus vesiculosus developed more rapidly, both in the aerial and root parts, compared to the control plants. The results presented in this example clearly show that phlorotannins allowed for intense stimulation of the symbiosis between corn plants and Rhizophagus intraradices, thus stimulating plant growth. EXAMPLE 3 - Effect of a phlorotannin extract derived from Fucus vesiculosus on the mineral content of the aerial parts of maize plants Pre-germinated maize seeds were sown in 0.9 m³ pots at a ratio of one seed per pot. The pots had been previously filled with a culture medium inoculated with the mycorrhizal fungus Rhizophagus intraradices. The plants were grown for 8 weeks under controlled conditions. The control group was watered 3 times a week with reverse osmosis water, while the treated group was watered with reverse osmosis water for the first week and, thereafter, with a phlorotannin extract derived from Fucus vesiculosus (prepared according to Example 1) diluted in water (at a ratio of 100 g / ha of phlorotannins). Both the control and treated groups were watered with reverse osmosis water during the first week. From the second week onward, reverse osmosis water was replaced with the phlorotannin extract in the treated group.The fertilizer application was carried out from the third week onwards with a 15 / 3 / 25 fertilizer, corresponding to the nitrogen / phosphorus / potassium content, respectively, at a rate of one weekly application in the irrigation water. The nitrogen, phosphorus, potassium, and calcium contents of the aerial parts of maize plants were measured after 8 weeks of cultivation. Five plants were used per group. Before analysis, the aerial parts were oven-dried and then ground. Total nitrogen content was measured according to the Dumas method, which involves combustion at 1200 °C in the presence of oxygen, purification of the combustion gases, conversion of the nitrogen oxides produced into elemental nitrogen, and quantitative determination of elemental N by catarometry. Total phosphorus, total potassium, and total calcium contents were measured by dry mineralization (according to the method of Maurice Pinta, Atomic Absorption Spectrometry: Application to Chemical Analysis, 1979). The dried and ground plant sample was calcined in a muffle furnace, after which the ash was collected with concentrated hydrochloric acid.The extract is evaporated to dryness and then collected with dilute hydrochloric acid. Quantitative determination is carried out on the diluted and volume-adjusted extract using inductively coupled plasma electrophoresis (ICP-AES). The application of the FV extract allows an increase in the nitrogen, phosphorus, potassium and calcium content in the aerial parts of corn plants. TABLE 6: Effect of a phlorotannin extract derived from Fucus vesiculosus on the mineral element content in the aerial parts of corn plants The results presented are expressed as a percentage of the mineral element's mass relative to the dry mass (% w / w dry mass), for example, in grams of mineral element / 100 g dry mass. In this case, it corresponds to the percentage of nitrogen, phosphorus, potassium, and calcium in a dry sample of the aerial parts of corn plants. The results presented in Table 6 show an increase in the mineral element content (nitrogen, phosphorus, potassium, and calcium) of the aerial parts of plants treated with phlorotannins from Fucus vesiculosus compared to the control plants. EXAMPLE 4 - Effects of a phlorotannin extract on rhizobial nodule formation The experiment was conducted using forage peas of the Solara variety. The forage peas were sown at a density of 15 seeds per pot, equivalent to a sowing density of 590 seeds / m². The pots contained a mixture of enriched peat, soil, and sand (1 / 3, 1 / 3, 1 / 3). Each group consisted of 8 pots. An inert substrate containing phlorotannin extract prepared according to Example 1 from Fucus vesiculosus was mixed with the soil at a rate of 100 kg / ha (equivalent to 100 g / ha of phlorotannins). In the control group, the extract was replaced with water. The cultures were grown for 5 weeks. After 5 weeks, the number of nodules and the dry matter content of the aerial parts were determined. A 37% increase in the number of nodules was observed compared to the control group. Similarly, the dry matter production of the aerial parts increased by 9% compared to the control group. Table 7: Effects of a phlorotannin extract on nodule formation The results presented in this example clearly show that phlorotannins strongly stimulated the symbiosis between corn plants and a rhizobium, thereby stimulating plant growth. EXAMPLE 5 - Effects of a phlorotannin extract on wheat yield The trial was conducted with Altria variety wheat, sown at a density of 160 kg / ha. The experimental design includes treatments with 4 repetitions. Each elementary plot measures 7 m x 2 m, which represents an area of ​​14 m2. Nitrogen fertilization (165 U, slightly limiting dose X-10%) was split into 3 applications of ammonium nitrate 33.5. The applications were made in the tillering (55 U), 1 cm spike (85 U) and last visible leaf (25 U) stages. The phlorotannin extract prepared according to Example 1 from Ascophyllum nodosum was applied at the mid-heading stage at a rate of 150 g / ha. The soil was of a silty-clay-sandy type with a pH of 8.1. Tabl: Ef n xr fl r nin riv A h ll mnmrlrn imi nl rigo The yield is expressed in relation to a dry matter content of 14.5%. q / ha: quintals per hectare The phlorotannin extract allows for a yield improvement of 6.2 q / ha, representing a 10.3% increase. EXAMPLE 6 - Effects of a phlorotannin extract on soybean fruiting The trial was conducted in a soybean crop. The soybeans were sown at a density of 70 seeds / m2. The phlorotannin extract prepared according to Example 1 from Fucus vesiculosus was applied at a ratio of 100 g / ha in two stages (2-3 leaves and beginning of flowering). The results are presented in Table 9. Table 9: Effects of a phlorotannin extract on the number of pods Phlorotannin extract promotes the vegetative development of the plant, as well as the formation of pods. EXAMPLE 7 - Effects of a phlorotannin extract on pear production and quality. The trial was carried out in a Williams pear orchard planted at a density of 3000 trees per hectare. The orchard was managed using a hedgerow system. The groups consisted of 4 elementary plots, each corresponding to a row of 5 trees. The phlorotannin extract produced according to Example 1 from Fucus vesiculosus was applied at a rate of 300 g / ha at the beginning of the flowering phase, with the percentage of open flowers estimated at more than 3%. Pear harvesting was carried out on 4 trees per plot, for a total of 16 trees per group. The border tree located between two groups was not included. To determine the average fruit weight, 100 fruits were weighed per replicate. Firmness was determined on 20 fruits per replicate using a penetrometer, which measures the force required to penetrate the fruit with a metal cylinder. In this test, the metal cylinder was a movable point with a diameter of 0.5 cm². The results were expressed in kg / 0.5 cm² and are presented in Table 10. Table 10: Effects of a phlorotannin extract on the production of eras A 6.2% increase in yield was observed, with a slight superiority in qualitative terms (average weight and firmness of the fruit) in the pear trees treated with the phlorotannin extract. EXAMPLE 8 - Effects of a phlorotannin extract on melon production The experiment was carried out in a climate-controlled and irrigated tunnel, with plastic mulch on the floor. Melon plants in root balls (Preco variety grafted onto Tézier rootstock), grown in a nursery, were transplanted at the 2-true-leaf stage. Plant management was carried out on 2 primary shoots. These were pruned at approximately the 8-leaf stage. Subsequently, the secondary shoots formed were pruned to the 2-leaf stage. Each elementary plot comprised 15 plants in a single row. The groups consisted of 4 replicates. The phlorotannin extract produced according to Example 1 from Ascophyllum nodosum was applied at a rate of 100 g / ha. The results are presented in Table 11. Table 11: Effects of a phlorotannin extract on melon production The results show that melons treated with the phlorotannin extract exhibited earlier production. Furthermore, the harvests were more abundant from the first days, and this difference persisted until the last day of harvest, with a 15.3% increase in cumulative weight and a 17.4% increase in the number of melons. EXAMPLE 9 - Examples of formulations incorporating phlorotannin extracts that can be used within the scope of the invention The following are presented as examples various fertilizer products usable according to the invention, with indications regarding the conditions of their application. A - AMENDMENTS a) CALCAREOUS AMENDMENT Lithotamnium 1000 kg Amendment 1 Phlorotannin extract q.s. 200 g / ha Application rate 1 t / ha Amendment 2 Calcium carbonate 1000 kg Phlorotannin extract q.s. 1000 g / ha Application rate 1 t / ha Amendment 3 1000 kg of plaster Phlorotannin extract q.s. 1000 g / ha Application rate 1 t / ha T / ha: tons per hectare b) ORGANIC AMENDMENT AND CROP SUPPORTS Substrate 500 kg Peat 500 kg Phlorotannin extract q.s. 500 g / ha Application rate 1 t / ha B - ROOT FERTILIZERS a) NP FERTILIZERS Lithotamnium 310 kg Potassium chloride 167 kg Urea 161 kg Ammonium sulfate 362 kg Phlorotannin extract q.s. 200 g / ha b) NPK + MgO FERTILIZERS Lithothamnium 158 kg Ammonium phosphate 116 kg Ammonium sulfate 186 kg Urea 156 kg Magnesium oxide 50 kg Potassium chloride 334 kg Phlorotannin extract q.s. 1000 g / ha C - ROOT NUTRIENT SOLUTIONS (HYDROPONICS, DRIP) a) NPK Mg SOLUTION Potassium nitrate 50 g / l Potassium phosphate 27 g / l Magnesium sulfate 49 g / l Phlorotannin extract 200 g / l (i.e., 1 g / l of the final solution applied to the plant) Dilution: 1 l per 200 l of water b) N Ca Mg SOLUTION Calcium nitrate 118 g / l Iron chelate 5 g / l Phlorotannin extract 100 g / l (i.e., 0.5 g / l of the final solution applied to the plant) Dilution: 1 l per 200 l of water

Claims

1. Use of phlorotannins, in particular extracted from brown algae of the Fucaceae family, to stimulate symbiosis between a plant and a mycorrhizal fungus.

2. Use according to claim 1, characterized in that the plant is a legume.

3. Use according to claim 2, characterized in that the phlorotannins also stimulate symbiosis with a rhizobium.

4. Use according to any one of claims 1 to 3, characterized in that the aforementioned phlorotannins are extracts from algae selected from the group consisting of species of the genera Fucus or Ascophyllum.

5. Use according to any one of claims 1 to 4, characterized in that the aforementioned extracts are obtained by a process generally comprising the following steps: washing, grinding, extraction (solid-liquid separation), and optionally, fractionation and concentration. 6.Use according to any one of claims 1 to 5, characterized in that the phlorotannins are supplied to the plant: - either in liquid form, in root nutrient solutions, in an amount of 0.1 to 100 g per liter, preferably on the order of 5 g per liter, - or in solid form, for example, in powdered or granulated fertilizers, in an amount of 10 to 1000 g, preferably on the order of 100 g per hectare.

7. Use according to any one of claims 1 to 6, characterized in that the phlorotannins also enable the plant to stimulate the uptake of one or more elements selected from nitrogen, phosphorus, potassium, and calcium.

8. A method for stimulating symbiosis between a plant and a mycorrhizal fungus, characterized in that it comprises applying to said plant or to the soil an effective amount of phlorotannins, in particular extracted from brown algae of the Fucaceae family. 9.A process according to claim 8, characterized in that the plant is a legume.

10. A process according to claim 8 or 9, characterized in that it also allows for the stimulation of symbiosis with a rhizobium.

11. A process according to any one of claims 8 to 10, characterized in that the application to the plant is carried out via the root system.

12. A process according to any one of claims 8 to 11, characterized in that the phlorotannins are used in an amount: - from 0.1 to 100 g per liter, and preferably on the order of 5 g per liter for applications in liquid form in root nutrient solutions, - from 10 to 1000 g, and preferably on the order of 100 g per hectare for applications in solid form in powder or granulated fertilizers. 13.A process according to any one of claims 8 to 12, characterized in that the phlorotannins also allow the plant to stimulate the absorption of one or more elements selected from nitrogen, phosphorus, potassium and calcium.