Amazon fungus improves soybean growth and development

Discovery could give rise to biofertilizer

23.06.2020 | 20:59 (UTC -3)
Cristina Tordin​

A fungus that occurs in the soil of the Amazon Rainforest has revealed itself to be an important stimulant for plant development. Researchers from Embrapa Environment (SP) evaluated more than a thousand strains of the fungus Trichoderma applied in conjunction with two sources of phosphorus, and found that many of them promote the growth of soybean plants. The results were published in the journal Scientific Reports of the group Nature.

The microorganism solubilizes the phosphorus present in the soil, allowing this mineral to be easily absorbed by the plant. As a result, soybeans grow faster and the producer can save on the application of this nutrient. In addition to saving money for the producer, its use reduces the risk of phosphorus being transported to bodies of water, providing sustainability to production. The discovery could give rise to a biofertilizer, in inoculant format, for important agricultural crops. The bioinoculants of Trichoderma They are formulated based on fungal structures, usually spores. Its application is through seed treatment or directly applied to the soil. They are used in several crops of economic importance, benefiting the germination and initial growth of plants. 

The increasing use of mineral fertilizers has contributed to reduce soil health, causing contamination. Thus, biofertilizers based on beneficial microorganisms can eliminate these problems and also reduce production costs.

The fungus-based product Trichoderma It can be applied to different agricultural crops, from vegetables to large crops such as soybeans, corn and beans. Furthermore, it has the extraordinary potential to colonize the root system and the rhizosphere, a basic requirement for the microorganism to establish itself and promote plant growth, increasing the supply of phosphorus.

"For future products, the choice of fungus application technology will depend on the development of formulations. In this case, we do not yet have a standardized formulation", explains the Embrapa researcher Itamar Melo

“We do have an efficient method of producing spores. Strains of this fungus, studied here, sporulate very quickly, between three and six days in natural cultivation media, an additional advantage to the products now available on the market. Some innovative actions regarding the development of an efficient biofertilizer would be to enhance the association of strains of the same fungal species with specific functions to promote plant growth, improve soil structure and health and control soil-inhabiting pathogens."

Research

Soybean plants inoculated with selected strains of Trichoderma were grown in soil with rock phosphate and triple superphosphate. The researchers observed an increase of more than 40% in the biomass of plants inoculated with the microorganism. And the efficiency of phosphorus absorption by the plants was increased by up to 141% compared to the group that did not have the Trichoderma sp

Biologist Laura Bononi, who used the research in her doctorate at the Luiz de Queiroz School of Agriculture at the University of São Paulo (Esalq / USP), reveals that the fungus was capable of producing different organic acids during the process. “These acids are important for releasing the phosphorus retained in iron and aluminum oxides, that is, for converting the phosphate present in the environment into di- or monobasic phosphates, which are readily available for absorption”, says the biologist, who was guided by Melo.

Phosphorus performs vital functions at all stages of plant development and its deficiency can reduce the growth and productivity of many agricultural crops. Acidic soils, quite common in Brazil, quickly retain this mineral applied as fertilizer and do not make it available to plants. “The use of phosphate-solubilizing microorganisms is a sustainable and promising strategy to manage this deficiency in agricultural soils,” says Melo, highlighting that this technology makes it possible to take advantage of the use of different types of rock phosphates from Brazilian mines. Currently, these phosphates are rarely used as fertilizers, which makes the country import this input. 

The importance of phosphorus

The scientist explains that nitrogen and phosphorus are the nutrients that most limit agricultural production and are essential in the initial development of plants. However, Brazilian soils naturally have a low amount of this element, which requires applications of phosphate in large quantities. Phosphorus is associated with three fundamental biochemical processes: energy production, respiration and photosynthesis. It also participates in enzymatic processes and makes up plant cell structures, such as nucleic acids and cell membranes. 

Although there is a large amount of phosphorus in the soil, its low availability for plants is one of the main obstacles to agricultural productivity. Crops can only absorb between 10% and 40% of the total mineral applied to the soil. This phenomenon is due to a high degree of reactivity that occurs between phosphorus and soil constituents, causing the fixation of the mineral or its precipitation with soil particles, making it unavailable for plant absorption. Corn, soy and sugar cane are the crops that receive most of the phosphate fertilizers used in Brazil. 

Amazon, storehouse of species

In addition to the vast plant and animal biodiversity, the Amazon Rainforest is also home to a vast microbiological diversity. Fungi, in particular, participate in the constant process of degradation of biomass generated in the biome, which makes the Amazon a valuable source of bioprospecting for these microorganisms and products generated by them. 

The application of microorganisms as biofertilizers is a promising approach to assist in agricultural production. These applications contributed to the growth of various crop species, increased plant biomass and total phosphorus content, and participated in phosphorus cycling without affecting the environment. Last year, Brazil launched its first inoculant aimed at solubilizing phosphorus. The result of a partnership between Embrapa and the company Bioma, the BiomaPhos results from the action of two bacteria and is used for corn cultivation.

Agricultural and pasture soils are composed of larger communities of these microorganisms involved in phosphorus availability. They are essential for providing the nutrient that is retained in the soil for plants through the mineralization and solubilization processes. Fungi have an advantage over bacteria as they are able to maintain an aggregate in the soil provided by the growth of their hyphae (filaments). In this way, it helps the plant to acquire nutrients, water and protects it from attack by phytopathogens.

Trichoderma to control white mold in soybeans

Among the various species present in nature, the Trichoderma harzianum It is the most commonly used in the biological control of plant diseases, prevailing in plant remains in various geographic regions. "O Trichoderma has an important mechanism of action on pathogens that attack important agricultural crops such as Fusarium spp. (red root rot), Sclerotinia sclerotiorum (white mold) and Rhizoctonia solani (root rot)”, explains the researcher Mauricio Meyer, from Embrapa Soja.

Embrapa estimates that approximately ten million hectares of soybean cultivation are infested by the fungus Sclerotinia sclerotiorum, which causes white mold. This disease manifests itself more severely in rainy years, mild temperatures and constant soil humidity. The main form of infection of plants by the fungus occurs preferentially in soybean petals, which serve as a substrate for the fungus at the beginning of the infection, before reaching stems and petioles. The disease hinders plant development and reduces productivity.

Trichoderma has been successfully used as a biological control agent for sclerotinia in soybeans. To achieve this, soil conditioning is necessary to promote maximum colonization by Trichoderma and thus reduce the potential for the disease in the area.

Meyer emphasizes that biological control is important, as the adoption of chemical control alone is not sufficient for good management of white mold in soybean farming; integration of practices is necessary. “We have to consider that even with the greatest efficiency of chemical control, inoculum production still occurs. Therefore, other management measures must be adopted together, to make it impossible to maintain the fungus during the off-season,” he explains.

The researcher reinforces the importance of soil conditioning through the direct sowing system on grass straw. “The straw works as a filter, preventing the spores of S. sclerotiorum reach soybean plants and initiate infection. Other benefits of straw on the soil are the increase in organic matter, which serves as a substrate for the Trichoderma, and the maintenance of humidity and reduction of soil surface temperature, fundamental conditions for the establishment of the biological control agent”, he highlights.

the fungus

The strains of Trichoderma have been one of the most studied fungi to improve the production and development of various crop species, mainly due to their capacity for symbiotic associations and control of root diseases. 

Trichoderma It is commonly studied for the control of phytopathogens and as a biofertilizer, since it is involved in the colonization of the rhizosphere, in the production of antifungal substances and phytohormones, attributes that make it one of the most successful biocontrol agents for plant diseases. 

It plays a crucial role in the hydrolysis of organic matter in the soil, mainly cellulose, improving its structure. Furthermore, it is easy to isolate, grows quickly and is capable of developing on different substrates, and producing a large amount of metabolites, such as antibiotics and auxins. 


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