The world has long begun a boom around organic products that must meet certain criteria, including being environmentally friendly. And how to achieve the desired purity, if almost all crops are susceptible to diseases caused by microbes? It is not easy to solve such a problem without “chemistry”. Therefore, scientists are thinking about how to make chemicals as harmless to plants and human health as possible. Alla PERFILYEVA, Senior Researcher of the Laboratory of Plant-Microbial Interactions of the Siberian Institute of Plant Physiology and Biochemistry of the Siberian Branch of the Russian Academy of Sciences, Candidate of Biological Sciences, took up the solution of this problem together with her scientific team. The research topic “Improvement of agricultural plants from bacterial and fungal phytopathogens using selenium nanocomposites obtained by chemical and microbiological synthesis” was supported by a grant from the President of the Russian Federation.
- Phytopathogenic microbes are the causative agents of diseases of cultivated plants, says Alla. They can be in the form of viruses, bacteria or fungi. Due to global climate change, the range of many pathogenic microbes is expanding, including spreading to new territories. Pathogens lead to the defeat of planting material – rotting of bulbs, tubers of plants. As a result, the growth of the plant slows down during the growing season: its size as a whole or its organs decrease – the leaves become smaller, the root system develops poorly. Pigmentation changes: yellowing occurs, the organs become pale green. Leaves and stems wither, cases of complete death of plants are not uncommon. All this, of course, negatively affects the crop.
– How to deal with it?
– To suppress phytopathogenic microorganisms, toxic pesticides are used. However, they act against fungi and are ineffective against bacteria. But such funds are undoubtedly needed.
- It turns out that phytopathogenic bacteria destroy everything and nothing can be done about it?
- It is unprofitable for phytopathogens to destroy everything, because they need a food base. If they completely exterminate host plants, then they simply will have nowhere to live and nothing to eat. Therefore, phytopathogens inhibit plants gradually.
The development of diseases is influenced by weather conditions, sometimes they turn out to be in favor of a person, not pathogens. For example, various rots, including late blight disease, develop more actively in cold and rainy summers, and dry and hot weather is unfavorable for them. Sometimes crop losses are significant and amount to 40-70%. One must take into account the fact that phytopathogens never work alone. As a rule, there is a complex effect of fungi and bacteria on plants. As a result, one infection (often fungi) weakens the plant organism, and the rest of the phytopathogens attack later.
- It turns out that some crops should not be grown at all – will bacteria eat them anyway?
- As a result of long-term selection, a person selected the most resistant varieties of cultivated plants. However, the evolution of phytopathogens goes in parallel with the evolution of host plants – they also become more tenacious.
– What drugs are currently being developed to solve the problem?
- Phytopathogenic microorganisms are very resistant to environmental factors, as they are able to spend part of their lives outside the host plant organism, being in the soil. Therefore, not all substances can affect their viability. This I know from my own experience testing various chemicals.
– Why did you decide to try selenium nanocomposites?
Selenium is an essential micronutrient for all living organisms. It is part of the enzymes necessary for the cell, has a high biological activity and an antioxidant effect. However, its content in the soil around the world is insufficient.
In the composition of nanocomposites, selenium is in the form of nanoparticles. They have no charge, their size is up to 100 nanometers. Compared to conventional compounds of chemical elements, nanoparticles need to be consumed in smaller volumes. In large quantities, they have a toxic effect.
When creating nanocomposites, nanoparticles are densely packed inside a large molecule (matrix). This is a natural polymer, for example, starch obtained from potatoes, or carrageenan, used as a thickener for the food industry, or arabinogalactan, a polysaccharide isolated from Siberian larch, as well as humic substances. Nanoparticles are not located on the surface of the nanocomposite, but inside, therefore they are unable to enter into chemical reactions.
How is bacteria destroyed?
– Natural polymers are attractive to pathogenic bacteria as food. They secrete special substances outside – exoenzymes, which are capable of breaking down large molecules outside the bacterial cell into smaller ones – oligomers and monomers. Bacteria feed on them. When the nanocomposite matrix is cleaved by exoenzymes, selenium nanoparticles are released.
They attach to the surface of the bacterial cell and act on the membrane potential, that is, the charge on the cell surface. As a result, fluid from the environment begins to actively enter the bacterial cell, which leads to the rupture of the bacterium.
At the same time, both selenium nanoparticles and matrices do not have a negative effect on plants. Moreover, we studied a number of substances – selenium nanocomposites in various natural polymer matrices – and found that they even stimulate the growth and development of plants, increase their resistance to phytopathogens in vitro, that is, “in test tube”, and productivity in field conditions. experiment.
At the same time, selenium does not accumulate in plant tissues after their treatment and does not have a detrimental effect on soil microorganisms, which indicates the safety of using nanocomposites. Moreover, they enrich the mineral nutrition of plants, increase their resistance to diseases. Thus, it turns out that selenium nanocomposites destroy phytopathogenic microorganisms and, in addition, have a growth-stimulating effect for plants without harming the environment.
- How long have you been working on this topic? What other results did you get?
– I started researching the biological activity of nanocomposites right after defending my Ph.D. thesis in 2013. Selenium nanocomposites are synthesized by the scientific group of Boris Sukhov at the Institute of Kinetics and Combustion of the Siberian Branch of the Russian Academy of Sciences. VV Voevodsky in Novosibirsk. At our Institute, I and my colleagues are engaged in nanocomposites: Irina Graskova, Chief Researcher of the Laboratory of Plant-Microbial Interactions, Doctor of Biology, Olga Nozhkina and Anastasia Gazizova, Leading Engineer, as well as students of the Biology and Soil Faculty of Irkutsk State University, who carry out research under my supervision for their term papers and dissertations.
We have studied the effect of a number of selenium-containing nanocomposites in matrices on the germination of radishes, soybeans, and potatoes. Found that in some cases they stimulate growth. For three years, from 2020 to 2022, in the course of field experiments, we studied the effect of selenium nanocomposites on potato productivity and found that they increased the number of tubers obtained from each plant.
In addition, we discovered the detrimental effect that selenium nanocomposites have on potato ring rot bacteria, Clavibactersepedonicus, and the late blight pathogen Phytophthora cactorum, which infects a wide range of crops, from apple trees to flowers.
Late blight is a disease of plants in which yellowing and wilting of leaves, rotting of fruits on the vine and even complete death of the plant are observed. Often found in representatives of the nightshade family – these are tomatoes and potatoes. Now we are studying how the preplant treatment of potato tubers with selenium nanocomposites affects the microbial composition (microbiome) of tubers from the potato crop.
For 10 years, we have studied a number of nanocomposites based on nanoparticles of metals – silver, copper, manganese, iron, as well as their various combinations. New interesting data have been obtained, according to which some nanocomposites have a very high biological activity: they stimulate the growth and development of plants, and have a high antibacterial effect. We have already applied for a patent on the registration of the biological activity of manganese nanocomposites.
– How much will the results of your research be in demand?
– Today, the use of nanotechnologies in various spheres of the national economy is being actively discussed. In medicine and veterinary medicine, nanoparticles are already widely used for cancer treatment and as antioxidants. The use of nanotechnologies in agrochemistry is promising due to the low volume of use of substances containing nanoparticles. At the same time, the costs are comparable to conventional disinfectants, and the effect of the use of nanoparticles is much higher. Due to the fact that the soil is poor in selenium, plants need appropriate mineral supplements. However, most of them do not completely dissolve in soil moisture and are absorbed by plants. Therefore, the need for treatment of planting material with selenium nanocomposites is obvious.
In addition, there is still not enough fundamental knowledge about the effect of nanoparticles on plant organisms, phytopathogenic microorganisms, and plant-microbial relationships. Our research fills these gaps. We have already conducted a large number of laboratory tests and field experiments, which gave us a fairly deep understanding of the problem. To use this knowledge in practice, approbation in an agricultural firm is needed. We will also do this, but later. Such work requires much larger volumes of nanocomposites than for laboratory studies. This is the task of synthetic chemists.
