One great challenge of modern agriculture is to find disease control mechanisms that are efficient alternatives to those of chemical options. The goal is to find coherent solutions that account for the need to increase productivity while respecting the environment.
In the framework of a public-private partnership Rizobacter, in conjunction with the area of bio-inputs from the National Institute of Agricultural Technology of Castelar (INTA Castelar according to its Acronym in Spanish), developed a highly-efficient pathogen biocontrol agent for wheat and soybean seeds with excellent results in field trials.
Thanks to many years of research and development, this bio-fungicide is already positioned to become an instrument for the control of pathogens that affect the seed germination process and seedling development on wheat and soybean. It is part of the next generation seed-care products that are 100% biological, apt for organic agriculture, and easier to handle, while also eliminating the environmental risk.
Natural and highly efficient solution for pathogen control
Formulation based on Trichoderma harzanium, a fungus recognized as one of the most important bio-control agents of diseases caused by pathogens associated to seeds and soil (such as: Fusarium spp., Bipolaris sorokiniana, Drechslera tritici repentis, Tilletia laevis, Ustilago tritici, Cercospora kikuchii, Phomopsis spp.). This bio-fungicide has equal or superior effectiveness when compared to chemical based seed-treatment products.
The TH2 strain of Trichoderma harzianum was used as the active ingredient for this product, isolated by the Institute of Microbiology and Agricultural Zoology of INTA Castelar in Argentina, and selected among 125 different strains. This strain has been identified as the most effective when it comes to controlling the development of important diseases on winter cereals.
This microorganism has three different ways for fighting the phytopathogenic fungi, while avoiding the generation of resistance. The three mechanisms are:
1. Competition: It has an important advantage competing for space and nutrients compared to pathogen fungi. It also improves the root structure, enhances the absorption of nutrients, and provides a better tolerance to stressful conditions.
2. Mycoparasitism: It develops around the pathogen and on its surface. It can penetrate to its interior through the action of the lytic enzymes (chitinase and ß-1,3-glucanase) that enables it to degrade the pathogen’s cellular wall.
3. Antibiosis: Lastly, the fungus secretes a great amount of antibiotic and metabolites that inhibit the pathogens, parasitic activity, preventing development and reproduction.
Innovation for improved performance
Today, there are two options to choose from when it comes to the formulation of biological fungicides: solid or liquid. Although the production of solids is easier, the advantages of the liquid formulations are clear. Here are a few:
• Sterility: Carrying out the multiplication in closed stainless-steel fermenters, it is easier to keep the product free from other microorganisms when using a liquid formulation. This not only extends the shelf life of the product when kept in its original container, but also ensures that only the required organism is used on the seed.
• Application quality: It is difficult to distribute powders evenly on seeds on its different areas. Liquid formulations allow an even distribution and a uniform adherence of the inoculum to the seed.
• Mixing possibilities: Without a doubt, liquid formulations are the easiest solution when applying different products simultaneously on the seed.
• Coloring: Some countries’ regulations establish that the treated seed should be quickly differentiated from the one that is not. The possibility of adding colorants to the liquid formulation allows to comply with these requirements.
• Environmental safety: Contrary to the powdered formulations that may drift during application, liquid formulations
Although the advantages for the final user may be clear, a high-quality liquid formulation is difficult to obtain and requires long hours of research and development. Only then a high purity product that guarantees sterilization can
Stages of development
These are some of the different stages carried out in the process of formulating the liquid and sterilized Trichoderma harzianum strain TH2.
1. Growth media selection: Selection of a media where the fungus can have an optimum conidia production. Modified S-Base Agar (MSBA), Modified Richard’s Agar (MRA), GK Agar, Medium Mix, Agar MMA were tested. Culture media evaluation was performed by rating each medium’s attribute such as carbon source (CS) / nitrogen source (NS) relationship, type of CS, type of NS, pH, cation and anion pool and complex nutrient sources.
2. Development of various formulations: Among those, different phosphate buffers, trehalose, glycerol, polyethylene glycol (PEG) and polyvinylpyrrolidone (PVP), gelatin, soybean meal, wheat flour and milk were tested.
3. Container selection: Various tests were carried out to determine which were the containers best suited for conserving the conidia produced by Trichoderma harzianum strain TH2. Various bladders from different materials and densities were used, as well as bottles and containers with cone-shaped bottoms.
In the trials in which formulations as well as the selection of containers were done, the determination of the number of viable cells over a certain period of time was analyzed. Presently, the product has a viability of six months in a bladder.
Parallel to the above-mentioned development stages, in vitro control of plant pathogens and field trails were carried out.
As a way of obtaining a value of the inhibition produced by the selected strain as a bio-controller, Trichoderma harzianum strain TH2 was tested against the fungal main pathogens of different crops in Petri dishes.
In all the cases, the observed inhibition value was higher than 60 percent, showing that this strain can effectively control pathogens on different crops.
Lastly, and in order to confirm the efficacy of the TH2 strain on real field conditions, a long set of field trials was carried out under various agroecological areas.