Scientists of the D.K. Zabolotny Institute of Microbiology and Virology of the NAS of Ukraine have isolated new strains of bacteria that inhabit the internal tissues of soybeans (these microorganisms are called endophytes) and have proven their positive effect on plants overcoming temperature and oxidative stresses. The use of endophytes improved plant growth and increased yield even under drought and high temperature conditions. Based on the isolated strains, the Institute developed a new preparation, Infitol. Field trials confirmed the effectiveness and prospects of using the preparation for agricultural crop growing. Scientists have clarified the main mechanisms of the positive effect of the developed preparation on plants and assert that its production has great potential.
Climate-resilient development of humanity is becoming increasingly relevant, given the increasing frequency of catastrophic weather events in various parts of the planet, including Ukraine. Agricultural crops suffer especially from extremely high temperatures and droughts. This reduces their yield, threatening food security. Therefore, many researchers from various fields have focused on increasing plant resistance to stress factors and developing climate-oriented biotechnologies for agriculture.
Scientists from the Department of General and Soil Microbiology of the D.K. Zabolotny Institute of Microbiology and Virology of the NAS of Ukraine also work on solving this problem. They focused on soil microorganisms that closely interact with plants, improve their nutrition and development, increase resistance to stress factors, and productivity. The Institute created a representative collection of agronomically useful microorganisms, which includes more than 300 strains – symbiotic, free-living, associative, and endophytic bacteria. These microorganisms have important ecological features: they exhibit their positive properties under extreme local climatic conditions (high temperatures, insufficient moisture), physicochemical properties of soils of various types, and are also capable of forming productive symbiotic systems with various plant varieties of Ukrainian and foreign breeding. Among such effective strains are soybean root nodule bacteria, on whose basis specialists of the D.K. Zabolotny Institute of Microbiology and Virology of the NAS of Ukraine developed the RizobinK complex inoculant (an inoculant is a biopreparation containing live strains of microorganisms used to treat seeds before sowing or roots of seedlings and saplings before planting). It contains an association of strains of root nodule bacteria Bradyrhizobium japonicum UKM B-6018, UKM B-6023, and UKM B-6035, and their biologically active metabolites – phytohormones, organic acids, amino acids, and others as well.
Manufacturers of microbial biopreparations show little interest in endophytic microorganisms, which, however, according to scientists, deserve special attention due to their properties. Endophytes inhabit the xylem tissues of conducting vessels and the intercellular space of plants and form mutually beneficial protocooperative relationships with them: they strengthen plants from within, protect them from phytopathogens and pests, activate mechanisms of stress resistance and antioxidant protection, and supply nutrients and growth-stimulating compounds.
Scientists of the Institute isolated six new strains of endophytic bacteria from surface-sterilized soybean nodules, studied their properties in laboratory and field experiments, and tested the effectiveness of the new strains in field trials. In experiments with soybean cultivation, seeds before sowing were treated comprehensively with root nodule bacteria from the RizobinK preparation and one of the isolated strains of endophytic bacteria of the Paenibacillus, Bacillus, and Pseudomonas genera. As a result, the scientists discovered a number of useful properties of the isolated strains for plants.
Why did the researchers decide to work specifically with soybeans? Because it is sensitive to high temperatures: each 1°C increase in average global temperature can reduce soybean yield by 3.1%. Drought is also one of the strongest abiotic stresses, negatively affecting root physiology, leaf structure, nutrient uptake, photosynthetic activity, and productivity. However, thanks to the complex endophytic-rhizobial inoculant developed at the D.K. Zabolotny Institute of Microbiology and Virology of the NAS of Ukraine, during droughts in the Kyiv region, the water regime of soybeans improved: water deficit decreased, water retention capacity increased, transpiration intensity decreased, meaning the plants were better hydrated. As a result, the adaptive potential of the plants increased, the symbiotic system formed better, and the yield of the Sculptor soybean variety increased by 36.2%. At the same time, the inoculant based on the new endophytic strain improved plant adaptability to adverse conditions and reduced oxidative stress. This is confirmed by lower accumulation of reactive oxygen species and increased catalase activity.
Moreover, the results of in vitro and in vivo experiments showed that the endophytic strains selected by the Institute’s specialists are also effective against the worsening phytopathological situation in agricultural crop fields, which is one of the accompanying problems of climate change. Regarding bacterial and fungal pathogens of soybean diseases, these strains exhibited a broad range of antagonistic and biocontrol activity. When soybean seeds were treated in field conditions on a natural infection background with the RizobinK composition together with endophytic strains, the effectiveness of plant protection against alternariosis ranged from 47.5% to 92%, and the productivity of various soybean varieties significantly increased (see the graph below). The average yield increase was 47%.
Effectiveness of protective action of endophytic-rhizobial inoculation against soybean alternariosis (%) and yield increase of various phytobacteria symbioses (%) under field conditions: 1 – Madison variety: RizobinK + Pseudomonas sp.6; 2 – Muza variety, RizobinK + Bacillus velezensis IMV B-8134; 3 – Sculptor variety, RizobinK + B. velezensis IMV B-8134.
Thus, to increase the yield and resistance of soybeans to pathogens under unfavorable phytosanitary environmental conditions, it is advisable to use endophytic bacteria in the cultivation technologies of the crop.
Based on these research results, scientists of the D.K. Zabolotny Institute of Microbiology and Virology of the NAS of Ukraine developed a new preparation containing endophytic bacteria – Infitol. The development has already passed the necessary toxicological tests; the strains Bacillus velezensis IMV B-8134 and B. velezensis IMV B-8135 are classified as hazard class IV, considered harmless to warm-blooded animals. The complete genome sequencing of these strains proved that their genetic material does not contain pathogenicity genes. Thus, biotechnological enterprises can already use these strains in the production of a unique innovative microbial preparation for crop production, which can also be useful in organic farming.
Infitol has already been tested in field conditions on soybean crops in the southern regions of Ukraine (Kherson and Odesa regions), once again confirming the effectiveness of the complex use of endophytic bacteria and rhizobial inoculation on both irrigated and rainfed lands.
For example, in Odesa region (a rainfed farming zone of the Southern Steppe of Ukraine), agroclimatic conditions during the soybean growing season were unfavorable because of large moisture deficit and a low soil moisture coefficient due to low precipitation and high soil moisture evaporation under high air temperatures. But if soybean seeds were treated before sowing with root nodule and endophytic bacteria, the plants showed resistance to stressful weather conditions. As a result, thanks to the complex endophytic-rhizobial inoculation, the yield of various maturity Diona and Sviatohor soybean varieties exceeded on average by 1.5 and 1.9 times, respectively, the yield of untreated plants.
Regarding the fields in Kherson region (these were irrigated farming plots), during the years of research, the seed yield of both studied soybean varieties in the co-inoculation variant with RizobinK + B. velezensis IMV B-8134 averaged 2.69 t/ha (for the ultra-early Diona variety) and 2.95 t/ha (for the mid-early Sviatohor variety), which exceeded the control indicators by 38–40%.
The calculation of economic efficiency shows that the complex endophytic-rhizobial inoculation of seeds of both soybean varieties using the preparative composition RizobinK + B. velezensis IMV B-8134 provides maximum indicators of net profit (about 13–17.5 thousand UAH/ha) at the lowest cost price (about 7.2–8.3 thousand UAH/t) and the highest profitability level (56.0–79.9%). In other words, pre-sowing inoculation of legume seeds with innovative endophytic-rhizobial preparations allows obtaining environmentally friendly products with low cost price and can therefore be an effective element of energy-saving farming.
As assured by the D.K. Zabolotny Institute of Microbiology and Virology of the NAS of Ukraine, under irrigation conditions, the proposed seed treatment scheme (complex endophytic-rhizobial inoculation) with the bacterial composite preparation RizobinK + B. velezensis IMV B-8134 will increase soybean yields on the Southern Steppe lands of Ukraine up to 3.05 t/ha for the ultra-early Diona variety and up to 3.21 t/ha for the mid-early Sviatohor variety, and will also contribute to increasing the content of available nitrogen forms in the soil and reducing chemical load on the environment, as all this can be achieved without mineral nitrogen fertilizers.
The work of scientists of the D.K. Zabolotny Institute of Microbiology and Virology of the NAS of Ukraine has demonstrated the high effectiveness of the selected strains of endophytic bacteria under current climate changes. The authors of the research consider the new endophytic strains with probiotic activity for plants a promising basis for multifunctional microbial phytobiotic preparations to create adaptive biotechnologies capable of supporting plant health and preventing yield losses under biotic and abiotic stresses.
Next, the specialists of the institution plan to focus on studying the spectrum of functional gene clusters related to the synthesis of substances that provide protection against pathogens, formation of systemic plant resistance to diseases, pests, and adverse climatic conditions. So, the work continues.
Information is provided by the D.K. Zabolotny Institute of Microbiology and Virology of the NAS of Ukraine.