Use of phorotannins as stimulants of mycorrhizal and rhizopous symbiosis

Abstract

The invention relates to the use of phlorotannins, particularly extracts of brown algae from the Fucaceae family, particularly of the Fucus or Ascophyllum genus, for stimulating the symbiosis between a plant and a mycorrhizal fungus or a rhizobium. The invention also relates to a fertilising product containing phlorotannins and to the uses thereof in a plant treatment method.

Description

Use of phlorotannins as a stimulant of mycorrhizal and rhizobial symbioses. The present invention, which has applications in the agricultural field, essentially relates to the use of phlorotannins, in particular extracted from brown algae, in particular from the family of fucaceae, in particular from the genus Fucus or ascophyllum, to stimulate the 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 fertilizing compositions such as, for example, fertilizers containing these phlorotannins, as well as a method for treating plants or soils using them. In the context of this description, the term "fertilizing composition" means any product whose use is intended to ensure or improve the physical, chemical or biological properties of soils as well as plant nutrition. Such a composition could be, for example, a fertilizer applied via the roots. We know that fertilizers are defined as fertilizing materials whose main function is to provide plants with elements directly useful for their nutrition (major 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. It is known that plants are capable of developing symbiotic associations with microorganisms to allow for the efficient acquisition of nutrients. Among the most economical and ecological symbiotic associations are the interactions between plants and mycorrhizal fungi, or between leguminous plants and nitrogen-fixing bacteria known as rhizobia. Plant-mycorrhizal fungi symbiosis Mycorrhizal fungi are capable of forming a close symbiosis with plant roots. They associate with more than 90% of plant species, including cereals, pastures, potatoes, corn, sunflowers, cotton, coffee, fruit trees, sugarcane, legumes, and ornamental plants. This symbiosis is absent 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, drawing nutrients from the soil. This network of filaments allows the plant to increase its root exploratory capacity and thus access nutrients inaccessible to the plant's root system. The plant-mycorrhizal fungi symbiosis results in improved fertilizer efficiency and reduced losses through leaching or erosion. In return, the plant provides sugars to the mycorrhizal fungi, which are necessary for their growth and for the synthesis of glomalin by the mycorrhizal filament network. Glomalin is a glycoprotein secreted by the filament network that contributes to soil structure and improves soil organic matter content. Indeed, 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 metal contamination. The agronomic effects associated with stimulating symbiosis between a plant and a mycorrhizal fungus are numerous. Stimulating symbiosis between a plant and a mycorrhizal fungus notably allows for: - to optimize the efficiency of fertilizers - to improve access to relatively immobile fertilizing elements such as phosphorus - to stimulate plant growth, flowering and / or fruiting - to improve crop yield and quality - to improve soil salinity tolerance - to improve resistance to climatic stresses, particularly drought or heat stress. - to reduce crop susceptibility to pathogens and nematodes, and to reduce losses through leaching and erosion - to improve soil structure. The degree of mycorrhization in a crop appears to be a factor influencing the yield and quality of agricultural products, with an impact on environmental protection. The degree of mycorrhization is determined by observing colored roots and counting the points containing hyphae, or by counting the number of spores or clusters. Today, we observe particularly low levels of mycorrhizal activity in soils due to various farming practices such as the massive use of fertilizers and pesticides, monoculture, lack of rotation, the development of non-mycorrhizal crops (rapeseed, sugar beet, cabbage, ...) or intensive tillage techniques. Legume-Rhizobium plant symbiosis Rhizobia (genus Rhizobium) are aerobic soil bacteria belonging to the Rhizobiaceae family. The symbiosis between a legume and a rhizobium is essential for the plant to acquire nitrogen in reduced form, and also for the rhizobia to obtain the nutrients necessary for their development. The legume provides nutrients to the rhizobia, which in turn capture nitrogen from the air and deliver it to their host. This symbiosis leads to the formation of new organs called root nodules. Root nodules are small swellings that form on the roots under the action of the rhizobia. These root nodules contain endosymbiotic cells of the legume plant that reduce atmospheric nitrogen into ammonium. This reduced nitrogen is then transferred to the plant and used for its growth.Symbiotic nitrogen fixation significantly improves the plant's nitrogen uptake. The importance of these rhizobia is therefore considerable, as they can fix up to 350 kg / ha / year of nitrogen. As with the symbiosis between a plant and a mycorrhizal fungus, cultivation practices can also affect the formation of the symbiosis between a legume plant and a rhizobium. This can result in a decrease in the formation of root nodules. There is therefore a significant need for new fertilizer products that address plant deficiencies, particularly by stimulating the symbiosis between a plant and a mycorrhizal fungus, and the symbiosis between legume plants. Seaweed is an abundant plant resource and has long been used in coastal regions as a soil fertilizer. Seed germination, improved yields, disease resistance, and longer fruit shelf life have been demonstrated following the treatment of various plants with seaweed extracts. These findings regarding plant growth and health were primarily attributed to the high betaine, phytohormone, polysaccharide, and trace element content of the seaweed used. It is in this context that the applicant has demonstrated, and this constitutes the basis of the present invention, that phlorotannins, particularly those extracted from brown algae of the Fucaceae family, surprisingly and unexpectedly stimulate mycorrhizal and rhizobial symbioses. This strong activity is supported by the stimulation of sporulation and nodulation. These phlorotannins can therefore be used as a supplement in fertilizing compositions such as fertilizers as activators of spore and nodule formation. Such compositions allow for increased absorption of nutrients from the soil and improved plant health, meeting the crop's growth needs, which will be expressed in particular in terms of improved yield and harvest quality. These compositions further improve fertilization efficiency and reduce losses through leaching and erosion problems. Thus, according to a first aspect, the present application aims to cover the use of phlorotannins, in particular extracted from brown algae of the fucaceae family, to stimulate the symbiosis between a plant and a mycorrhizal fungus. The useful phorotannins according to the invention are polyphenols present specifically in the cell walls and cells of brown algae of the family Fucaceae. Phlorotannins represent between 5 and 200 mg / g of the seaweed's dry weight. In a 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-limiting examples of legumes include soybeans, peanuts, beans, peas, lentils, chickpeas, broad beans, field beans, vetches, chickling vetch, alfalfa, clover, lupins, mung beans (sprouted soybeans), licorice, rosewood, bird's-foot trefoil, sainfoin, rooibos, and fenugreek. In one particular embodiment, phlorotannins also stimulate symbiosis between a leguminous plant and a rhizobium. Preferably, this stimulation of symbiosis is combined with stimulation of symbiosis with a mycorrhizal fungus. This application also aims to cover the use of phlorotannins, particularly those 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 seaweed extracts selected from the group consisting of species of the genus Fucus and Ascophyllum, in particular selected from the group consisting of the species Fucus vesiculosus, Fucus serratus and Ascophyllum nodosum. Phlorotannin-rich seaweed extracts that can be used in the context of the present invention can be obtained from the aforementioned seaweed species by a process generally comprising the following steps: washing, grinding, extraction (solid-liquid separation) and optionally fractionation and concentration. The resulting extract can be more or less concentrated depending on the intended use. Complete dehydration of this extract, allowing for presentation in a water-soluble powder form, can be achieved, for example, by drum dryer or spray drying. The extraction conditions and the type of algae will be chosen so that the resulting extract has the desired concentration for the intended application. These choices can be easily made by a person skilled in the art, particularly by taking into account the general guidelines that follow. Generally, the amount of phlorotannins applied to plants is 10 to 1000 g / ha, and preferably around 100 g / ha for applications in solid form in powdered or granular fertilizers. In a particular embodiment, phlorotannins also stimulate the plant's absorption of one or more elements selected from nitrogen, phosphorus, potassium, and calcium. For the purposes of this invention, "stimulating absorption" means an increased absorption and / or an improvement in absorption mechanisms. Thus, in a particular embodiment, phlorotannins also stimulate the plant's absorption 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 absorption of one or more elements selected from nitrogen, phosphorus, potassium, and calcium. Thus, in a particular embodiment, phlorotannins are supplied to the plant in an effective amount to increase the plant's absorption 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 make it possible to increase the content in the plant of one or more of the aforementioned elements 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 by at least 50%. Increased absorption is measured by determining the nitrogen, phosphorus, potassium, and / or calcium content in the plant. The term "increase" refers to the plant's content before phlorotannins were applied, for example, compared to a plant that received no phlorotannins. The nitrogen, phosphorus, potassium, and / or calcium content is expressed as w / w of dry mass, which corresponds to the mass of nitrogen, phosphorus, potassium, and / or calcium contained in a dried plant sample. The nitrogen, phosphorus, potassium, and / or calcium content is measured using an appropriate analytical method. The present invention also aims to protect the use of phlorotannins, particularly those extracted from brown algae of the Fucaceae family, to stimulate the absorption in a plant of one or more elements selected from nitrogen, phosphorus, potassium, and calcium. In a particular embodiment, the phlorotannins are supplied to the plant in an amount effective in increasing the plant's absorption 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 make it possible to increase the content in the plant of one or more of the aforementioned elements 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 by at least 50%. According to a second aspect, the present application aims to protect a process for stimulating symbiosis between a plant and a mycorrhizal fungus, characterized in that it includes the application to said plant or to soils of an effective quantity of phlorotannins, in particular extracted from brown algae of the family Fucaceae. In one particular embodiment, the plant is a legume. Thus, the method according to the present invention also makes it possible to stimulate symbiosis between a legume and a rhizobium. Preferably, the stimulation of symbiosis between a legume and a rhizobium is added to the stimulation of symbiosis with a mycorrhizal fungus. This application also aims to cover a process for stimulating symbiosis between a leguminous plant and a rhizobium, characterized in that it includes the application to said plant or to soils of an effective quantity of phlorotannins, in particular extracted from brown algae of the Fucaceae family. Advantageously, the application to plants will be carried out via the roots. The effective quantity of phlorotannins supplied to plants is from 0.1 g to 100 g per litre and preferably around 5 g per litre for liquid applications in root nutrient solutions (hydroponics, drip irrigation, etc.) or from 10 to 1000 g / ha and preferably around 100 g / ha for solid applications in powdered or granular fertilizers. In a particular embodiment, phlorotannins also allow the plant to stimulate the absorption of one or more elements chosen from nitrogen, phosphorus, potassium and calcium. The present invention also aims to protect a method for stimulating the absorption in 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 soils of an effective quantity of phlorotannins, in particular extracted from brown algae of the family Fucaceae. In a particular embodiment, phlorotannins are applied to the plant or soil in an amount effective in increasing the plant's absorption 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 increase the plant's content 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%. According to a third aspect, the present application aims to protect a fertilizer product, characterized in that it comprises an effective quantity of phlorotannins, in particular extracted from brown algae of the family Fucaceae, possibly in association with one or more fertilizer materials.Advantageously, the fertilizer product is characterized in that it presents itself as: - either in liquid form and containing a quantity of phlorotannins of 0.1 to 100 g per litre, and preferably of the order of 5 g per litre; - either in solid form, particularly in the form of powder or granules, and in that it contains a quantity of phlorotannins allowing an input of 10 to 1000 g and preferably of the order of 100 g per hectare. Advantageously, the fertilizer product according to the invention is available in various forms, such as: - an amendment, in particular a limestone amendment or an organic amendment - a fertilizer, in particular a root fertilizer - a nutrient solution, in particular a root nutrient solution. In a particular embodiment, the fertilizer product comprises an effective quantity of phlorotannins, notably extracted from brown algae of the Fucaceae family, in combination with one or more fertilizing materials. Advantageously, the fertilizing material is a source of calcium, notably calcium carbonate, calcium sulfate, gypsum, and / or phosphogypsum. In particular, the combination of phlorotannins and the calcium source, notably calcium carbonate, optimally stimulates the symbiosis between the plant and the mycorrhizal fungus. Examples of fertilizer products according to the invention include lime amendments, organic amendments and growing media, NP, PK, NPK, etc. type root fertilizers, and root nutrient solutions. Fertilizing substances that can be used in association with phlorotannins can be of various kinds and chosen for example from urea, ammonium sulfate, ammonium nitrate, natural phosphate, potassium chloride, ammonium sulfate, magnesium nitrate, manganese nitrate, zinc nitrate, copper nitrate, phosphoric acid, boric acid. The present invention finds application in the treatment of a very wide variety of plants. Among these, we will mention in particular: - major crops such as cereals (wheat, corn, sugar cane, ...), - protein crops (peas), - oilseeds (soybeans, sunflowers), - the vine - meadow plants useful for animal feed, - specialized crops such as in particular market gardening (lettuce, spinach, tomato, melon), vines, arboriculture (orange tree, pear, apple, nectarine), or horticulture (roses). The term "plant" in this application means the plant considered as a whole, including its root system, vegetative system, seeds and fruits. The present invention will now be illustrated by the following non-limiting examples. In these examples, and unless otherwise indicated, percentages are expressed by weight and the temperature is ambient temperature. EXAMPLE 1 - Process for preparing phlorotannins usable within the scope of the invention A - General description a) Preparation of an extract of phlorotannins from Ascophyllum nodosum The phlorotannins fraction was obtained by aqueous extraction of fresh algae (200 g of Ascophyllum nodosum per liter of water). The extraction was an acid hydrolysis (pH 3) carried out under stirring for 48 hours, with 1 hour of heating at 90-100 °C. The extract was then filtered through a membrane (80 µm porosity). b) Preparation of a phlorotannin extract from Fucus vesiculosus The phlorotannins fraction was obtained by aqueous extraction of fresh algae (200 g of Fucus vesiculosus per litre of water). The extraction was an acid hydrolysis (pH 3) carried out under stirring for 48 hours 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 type Ascophyllum nodosum or Fucus vesiculosus were subjected to two successive washes in a water tank in order to remove sand and gravel. The washed algae were drained and then crushed into pieces (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 ground algal cells were micro-bursted using an ULTRA-TU AX® homogenizer to facilitate extraction. The separation operation takes place after the extraction steps. d) Separation The soluble fraction rich in phlorotannins was separated from the algal debris by centrifugation (solid-liquid separation). The centrifuged extract was then filtered either through a diatomaceous earth filter or a plate filter, and then filtered again through a membrane down to 1 pm. The filtrate thus obtained comprises 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 falling-float evaporator, so that the dry extract represents 10 to 60% by weight of it. Total dehydration can also be achieved, for example, by drum dryer or by spray drying when a presentation in water-soluble powder form is desired. Following the procedure described above, various phlorotannin extracts were prepared from two species of brown algae of the genera Ascophyllum and Fucus. The composition of these dry phlorotannin extracts is presented in Table 1 below. TABLE 1: Composition of phlorotannin extracts from brown algae EXAMPLE 2 - Effects of a phlorotannin extract on the sporulation of Rhizophaus intraradices and on biomass production in maize Pre-germinated maize seeds were sown in 0.9 L pots, one seed per pot. The pots were pre-filled with a culture medium inoculated with the mycorrhizal fungus Rhizophagus intraradices. The plants were grown for 8 weeks under controlled conditions. The plants were watered three times a week with reverse osmosis water for the control treatment and with reverse osmosis water for the first week followed by phlorotannin extract prepared according to Example 1 diluted in water (at a rate of 100 g / ha of phlorotannins) for the treated treatment. Both the control and the treatment were watered with reverse osmosis water during the first week. From the second week onward, reverse osmosis water was replaced with phlorotannin extract. Fertilizer was applied from the third week with a 15 / 3 / 25 fertilizer, corresponding to the Nitrogen / Phosphorus / Potassium content respectively, at a rate of one application per week in the watering water.Two extracts of phlorotannins were tested: one from Ascophyllum nodosum (AN Extract) and another from Fucus vesiculosus (FV Extract). Rhizophagus intraradices sporulation controls were performed after 6 and 8 weeks of culture. For each control, 5 plants per treatment were analyzed. Fungal material was extracted from each plant, and spore clusters were counted under a binocular microscope. For the FV extract, measurements of aboveground and root biomass of maize plants were carried out after 8 weeks of culture. 5 plants per treatment were analyzed. Both phlorotannin extracts had 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 increased the fresh matter content of the aboveground and root parts of the maize plants. TABLE 2: Effect of 2 phlorotannin extracts on the number of spore clusters of Rhizophagus intraradices The results presented in Table 2 show a clear increase in the average number of spore clusters for plants treated with phlorotannins, compared to control plants. TABLE 3: Effect of a phlorotannin extract from Fucus vesiculosus on the number of spores per cluster of Rhizophagus intraradices The results presented in Table 3 show an increase in the number of clusters with more than 10 spores for plants treated with phlorotannins from Fucus vesiculosus, compared to control plants. TABLE 4: Effect of a phlorotannin extract from Ascophyllum nodosum on the number of spores per cluster of Rhizophagus intraradices <10 10-19 20-29 30-39 40-49 >50 Witness 37 27 17 11 3 5 6 weeks Treaty 16 42 19 7 7 9 Witness 50 27 11 8 1 3 8 weeks Treated 31 45 13 6 1 4 The results presented in Table 4 show an increase in the number of clusters with more than 10 spores for plants treated with phlorotannins from Ascophyllum nodosum, compared to control plants. TABLE 5: Effect of a phlorotannin extract from Fucus vesiculosus on the growth of maize plants The results presented in Table 5 show that plants treated with phlorotannins from Fucus vesiculosus developed more rapidly, both for aerial and root parts, compared to control plants. The results presented in this example clearly show that phlorotannins strongly stimulated the symbiosis between maize plants and Rhizophagus intraradices, thus stimulating plant growth. EXAMPLE 3 - Effect of a phlorotannin extract from Fucus vesiculosus on the mineral content of the aerial parts of maize plants Pre-germinated maize seeds were sown in 0.9 L pots, one seed per pot. The pots were pre-filled with a culture medium inoculated with the mycorrhizal fungus Rhizophagus intraradices. The plants were grown for 8 weeks under controlled conditions. The plants were watered three times a week with reverse osmosis water for the control treatment and with reverse osmosis water for the first week, followed by a phlorotannin extract from Fucus vesiculosus (prepared according to Example 1) diluted in water (at a rate of 100 g / ha of phlorotannins) for the treated treatment. Both the control and the treated treatment were watered with reverse osmosis water during the first week. From the second week onward, reverse osmosis water was replaced with the phlorotannin extract for the treated treatment.Fertilizer was applied from the third week with a 15 / 3 / 25 fertilizer, corresponding to the Nitrogen / Phosphorus / Potassium content respectively, at a rate of one application per week in the watering water. The nitrogen, phosphorus, potassium, and calcium content of the aboveground parts of maize plants was measured after 8 weeks of cultivation. Five plants per treatment were used. Before analysis, the aboveground parts were oven-dried and then ground. Total nitrogen content was measured according to the Dumas method, which consists of combustion at 1200°C under oxygen, purification of the combustion gases, conversion of the nitrogen oxides produced into elemental nitrogen, and determination of elemental nitrogen by catarrhometry. Total phosphorus, total potassium, and total calcium content 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 material sample was calcined in a muffle furnace, and the ash was then treated with concentrated hydrochloric acid.The extract is evaporated to dryness and then reconstituted with dilute hydrochloric acid. The assay is performed on the diluted and volumetrically determined extract by inductively coupled plasma optical emission spectrometry (ICP-AES). The application of the FV extract allows an increase in the nitrogen, phosphorus, potassium and calcium content of the aerial parts of corn plants. TABLE 6: Effect of a phlorotannins extract from Fucus vesiculosus on the mineral content of the aerial parts of maize 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, grams of mineral element per 100g dry mass. Here, this corresponds to the percentage of nitrogen, phosphorus, potassium, and calcium in a dried sample of maize plant aerial parts. 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 control plants. EXAMPLE 4 - Effects of a phlorotannin extract on the formation of rhizobial nodules The experiment was conducted on Solara variety forage peas. The forage peas were sown at a rate 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 treatment consisted of 8 pots. An inert substrate to which the phlorotannin extract prepared according to Example 1 from Fucus vesiculosus had been added was mixed into the soil at a rate of 100 kg / ha (equivalent to 100 g / ha of phlorotannins). For the control, the extract was replaced with water. The cultures were grown for 5 weeks. After 5 weeks of cultivation, 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. At the same time, dry matter production from the aerial parts increased by 9% compared to the control. Table 7: Effects of a phlorotannin extract on nodule formation MS: Dry matter The results presented in this example clearly show that phlorotannins have made it possible to strongly stimulate the symbiosis between corn plants and a Rhhizobium and thus stimulate plant growth. EXAMPLE 5 - Effects of a phlorotannin extract on wheat yield. The trial was carried out on Altria variety wheat, sown at a density of 160 kg / ha. The experimental design includes 4 replicates. Each elementary plot measures 7m x 2m, for a total 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 at the tillering stage (55 U), 1 cm ear stage (85 U) and last leaf visible stage (25 U). Phlorotannin extract manufactured according to example 1 from Ascophyllum nodosum was applied at the mid-heading stage at a rate of 150g / ha. The soil was a sandy loam type with a pH of 8.1. Table 8: Effects of a phlorotannin extract from Ascophyllum nodosum on wheat yield Yield is expressed relative to a dry matter content of 14.5%. q / ha: quintals per hectare Phlorotannin extract improves yield by 6.2 q / ha, representing a 10.3% increase. EXAMPLE 6 - Effects of a phlorotannin extract on soybean fruiting The experiment was carried out on a soybean crop. The soybeans were sown at a density of 70 grains / m2. The phlorotannin extract produced according to example 1 from Fucus vesiculosus was applied at a rate of 100g / ha at 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 MS = Dry mass. Phlorotannins 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 conducted on a Williams pear orchard planted at a density of 3000 trees per hectare. The orchard was managed as a fruit hedge. The modalities are composed 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 stage, the rate of open flowers was estimated to be greater than 3%. The pears were harvested from 4 trees per plot, for a total of 16 trees per treatment. The border tree located between two treatments was not included. To determine the average fruit weight, 100 fruits per replicate were weighed. Firmness was determined from 20 fruits per replicate. Firmness was assessed using a penetrometer, which measures the force required to penetrate a metal cylinder into the fruit. In this trial, the metal cylinder was a movable tip measuring 0.5 cm². The results were therefore expressed in kg / 0.5 cm² and are presented in Table 10. Table 10: Effects of a phlorotannin extract on pear production A 6.2% increase in yield was observed, with a slight improvement in quality (average fruit weight and firmness), for pear trees treated with phlorotannin extract. EXAMPLE 8 - Effects of a phlorotannin extract on melon production The experiment took place in a heated and irrigated tunnel with plastic mulch covering the soil. The melon seedlings (Preco variety grafted onto Tézier rootstock), grown in a nursery, were transplanted at the 2-true-leaf stage. The plants were trained on two primary branches. These were topped at approximately eight leaf nodes. Then, the secondary branches that formed were pruned to two leaf nodes. Each elementary plot contains 15 plants in a single row. The treatment consists of 4 replicates. The phlorotannin extract produced according to example 1 from Ascophyllum nodosum was applied at a rate of 100g / 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 phlorotannin extract exhibited earlier production. Furthermore, yields were higher 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 Various fertilizer products that can be used according to the invention will be given below as examples, with indications of the conditions of their implementation. A - AMENDMENTS a) LIMESTONE AMENDMENT Amendment 1 Lithothamnium 1000 kg Phlorotannin extract q.s. 200 g / ha Application rate 1 t / ha Amendment 2 Calcium carbonate 1000 kg Phlorotannin extract QSP 1000 g / ha Application dose 1 T / ha Amendment 3 Gypsum 1000 kg Phlorotannin extract q.s. 1000 g / ha Application rate 1 t / ha T / ha: tonnes per hectare b) ORGANIC AMENDMENT AND GROWING MEDIUM 500 kg of potting soil Peat 500 kg Phlorotannin extract QSP 500 g / ha Application rate lT / ha B - ROOT FERTILIZERS a NP FERTILIZERS Lithothamnium 310 kg, Potassium chloride 167 kg, Urea 161 kg Ammonium sulfate 362 kg Phlorotannin extract q.s. 200 g / ha CROPS APPLICATION DOSE (kg / ha) Pastures Cereals 200 - 400 Corn b) PK + MqQ FERTILIZER Lithothamnium 158 kg Ammonium phosphate 116 kg Ammonium sulfate 186 kg Urea 156 kg Magnesium oxide 50 kg Potassium chloride 334 kg Phlorotannin extract QSP 1000 g / ha C - ROOT NUTRIENTS SOLUTIONS HYDROPONICS. DRIP IRRIGATION a) NPK SOLUTION Mq Potassium nitrate 50 g / L Potassium phosphate 27 g / L Magnesium sulfate 49 g / L Phlorotannins extract 200 g / L (i.e., 1 g / L of final solution applied to the plant) Dilution 1 L per 200 L of water b) SOLUTION N Ca Mq Calcium nitrate 118 g / L Iron chelate 5 g / L Phlorotannin extract 100 g / L (i.e. 0.5 g / L of final solution applied to the plant) Dilution: 1 L per 200 L of water

Claims

DEMANDS 1. Use of phlorotannins, particularly those 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 leguminous plant.

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

4. Use according to any one of claims 1 to 3, characterized in that the aforementioned phlorotannins are extracted from algae selected from the group consisting of species of the genus 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 a quantity of 0.1 to 100 g per liter, and preferably in the order of 5 g per liter, - either in solid form, for example in powdered or granular fertilizers in a quantity of 10 to 1000 g and preferably in the order of 100 g per hectare.

7. Use according to any one of claims 1 to 6, characterized in that the phlorotannins further enable the plant to stimulate the absorption 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 the application to said plant or to soils of an effective quantity of phlorotannins, in particular extracted from brown algae of the family Fucaceae.

9. A method according to claim 7, characterized in that the plant is a leguminous plant.

10. Method according to claim 8, characterized in that it further enables the stimulation of symbiosis with a rhizobium.

11. Method of any one of claims 7 to 9, characterized in that the application to the plant is carried out via the root route.

12. A process according to any one of claims 7 to 10, characterized in that phlorotannins are used in a quantity: - from 0.1 to 100 g per liter, and preferably around 5 g per liter for liquid applications in root nutrient solutions, - from 10 to 1000 g and preferably around 100 g per hectare for inputs in solid form, for example, in powdered or granular fertilizers.

13. A method according to any one of claims 8 to 12, characterized in that the phlorotannins further enable the plant to stimulate the absorption of one or more elements selected from nitrogen, phosphorus, potassium and calcium.

14. Fertilizing product, characterized in that it comprises an effective quantity of phlorotannins, in particular extracted from brown algae of the family Fucaceae, possibly in association with one or more fertilizing materials.

15. Fertilizing product according to claim 12, characterized in that it is presented as: - either in liquid form and containing a quantity of phlorotannins of 0.1 to 100 g per litre, and preferably of the order of 5 g per litre; - either in solid form, particularly in the form of powder or granules, and in that it contains a quantity of phlorotannins allowing an input of 10 to 1000 g and preferably of the order of 100 g per hectare.