**4. Ways to Improve the Productivity of the Soybean-Rhizobial Symbiosis**

One of the objects with prospects in biotechnology are cyanobacteria because of their ability in photosynthesis, nitrogen fixation, the synthesis of biologically active substances and growth activating substances. These substances positively influence on soil fertility and the activity of soil biota. Cyanobacteria are closely linked to the bacteria such as *Rhizobium, Agrobacterium, Pseudomonas*, and are capable of forming a new stable association that opens the perspective for the creation of efficient microbial consortia and preparations based on them. Positive results were obtained when using in agricultural biotechnology artificial al‐ gae-rhizobial associations to inoculate the seeds of lotus, peas and clover. To date, it has been proved that under the influence of artificial consortia on the basis of *Nostoc* and various *Rhizobium* the effect of nitrogenation is enhanced on leguminous plants [6, 68-70].

The co-treatment of lucerne seeds by nitrogen-fixing bacteria and cyanobacteria *Nostoc punc‐ tiforme*, as well as by their binary compositions stimulates plant growth and development. It was found that the most effective method was co-inoculation by cyanobacteria with certain Tn5-mutants of *Rhizobium* when compared to inoculation by monocultures [71]. We have al‐ so studied the reaction of soybean *Glycine max* (L.) Merr. to inoculation by algal-rhizobial com‐ positions based on the nodule bacteria *Bradyrhizobium japonicum*, and cyanobacteria *Nostoc punctiforme* [72]. It is shown that the inoculation of soybean seeds by algal-rhizobial compo‐ sitions enhances germination and positively influences seedling formation. The inclusion of cyanobacteria into the inoculation suspension of rhizobia and Tn5-mutants in certain combi‐

nations can stimulate the growth and development of soybean, the accumulation of photosyn‐ thetic pigments in the leaves and the protein content in seeds. However, it does not have a significant effect on the activity of nitrogen-fixing nodules, and plant productivity. This da‐ ta indicates the need to find effective algal-rhizobial complex compositions to inoculate soy‐ bean plants by the optimal selection of the strains of bacteria and the ratio of inoculating agents. In our opinion further study is also required of the algal-rhizobial compositions cre‐ ated on the basis of microorganisms with genetically modified properties.

Creation and selection of compatible algal-rhizobial associations, including the axenic cul‐ tures of cyanobacteria and nodule bacteria as well as their Tn5-mutants may be one of the methods of biologically stimulating legume-rhizobial symbiosis, which enhances the signifi‐ cance of the interaction of rhizobia with plants and the efficiency of bacterial preparations based on them.

In the formation of legume-rhizobial symbiosis the essential components of the interaction of the symbiotic partners are polysaccharides which are synthesized by nitrogen-fixing bac‐ teria. Perhaps it was under the influence of these substances, acting as elicitors in the early stages of the morphogenesis of nodules, that gene activation occurrs for a number of plant genes that "sit in silence" in the uninoculated plant roots.

It has been suggested that the polysaccharides of non-rhizobial origin, as well as glycopoly‐ mers of rhizobia, are able to mimic the action of phytohormones and stimulate the processes of nodulation and morphogenesis in the legume-rhizobial symbiosis [73]. It is shown that the cells of nodule bacteria during the action of exogenous polysaccharides (Baktozol) in‐ creased in growth, produced more biomass and changed the activity of some enzymes of the nitrogen exchange [74, 75]. The stimulating effect of the synthetic polysaccharide (PS MOD-19) on the growth of rhizobia, biomass accumulation and changes in their metabolism during the growth of bacteria on solid and liquid media in the presence of the biopolymer was later revealed. During the processing of the seeds of peas (*Pisum sativum* L.) prior to sowing whith PS MOD-19 there was found an increased rhizogenesis in plants, an increased peroxidase activity in plant cells, as well as the increase of the effectiveness of symbiosis as a whole due to secondary formation of nodules on side roots and the prolonging of the period of their active nitrogen fixation [76]. In this regard, synthetic polysaccharides may be of in‐ terest as biologically active compounds for practical application, in particular, for the expan‐ sion of the range of substances that can stimulate the growth activity of rhizobia and, to a greater extent, enhance and prolong the activity of nitrogen-fixing nodules formed on roots of leguminous plants. The latter circumstance is of particular importance for legumes with a short vegetation period, of which the most vivid representative is the pea [73]. In our opin‐ ion, further study of the stimulating effect of polysaccharides of different origin is a promis‐ ing direction of improving the efficiency of legume-rhizobial symbiosis.

Our studies also show the effectiveness of biological products of nodule bacteria modified by homologous lectin, and the economic feasibility of their use [47, 49-51, 77-79]. In accord‐ ance with the existing concepts about the mechanisms of interaction of plants with rhizobia, polysaccharides of the latter are a factor which provides a "recognition" by the bacteria of the corresponding host plant through complementary binding to the plant lectin. Lectins are proteins that have the ability to reversibly and selectively bind to carbohydrates and carbo‐ hydrate parts of biopolymers without changing the covalent structure of the latter [77, 79]. Along with other biologically active substances legume lectins during the germination of seeds secrete themselves into the environment [21]. These proteins stimulate the prolifera‐ tion and active movement of soil microorganisms to the roots, and influence the growth of microsymbionts and the synthesis by them of exoglycans [48]. Plant lectins are regarded as one of the factors of effective symbiosis, which is also proposed for consideration when de‐ veloping and implementing new approaches to the management of production processes in legume plants [77]. It is known that treatment of rhizobia by plant lectin specific to them has a positive effect on their virulence and competitiveness [34], and also increases the nitrogenfixing activity of root nodules. Lectin acts on the biosynthesis of nitrogenase [58, 59] in the bacterial cell. As a consequence, pre-incubation of rhizobia with homologous lectin enhan‐ ces the growth processes of plants and increases the productivity of the symbiosis [47].

nations can stimulate the growth and development of soybean, the accumulation of photosyn‐ thetic pigments in the leaves and the protein content in seeds. However, it does not have a significant effect on the activity of nitrogen-fixing nodules, and plant productivity. This da‐ ta indicates the need to find effective algal-rhizobial complex compositions to inoculate soy‐ bean plants by the optimal selection of the strains of bacteria and the ratio of inoculating agents. In our opinion further study is also required of the algal-rhizobial compositions cre‐

A Comprehensive Survey of International Soybean Research - Genetics, Physiology, Agronomy and Nitrogen

Creation and selection of compatible algal-rhizobial associations, including the axenic cul‐ tures of cyanobacteria and nodule bacteria as well as their Tn5-mutants may be one of the methods of biologically stimulating legume-rhizobial symbiosis, which enhances the signifi‐ cance of the interaction of rhizobia with plants and the efficiency of bacterial preparations

In the formation of legume-rhizobial symbiosis the essential components of the interaction of the symbiotic partners are polysaccharides which are synthesized by nitrogen-fixing bac‐ teria. Perhaps it was under the influence of these substances, acting as elicitors in the early stages of the morphogenesis of nodules, that gene activation occurrs for a number of plant

It has been suggested that the polysaccharides of non-rhizobial origin, as well as glycopoly‐ mers of rhizobia, are able to mimic the action of phytohormones and stimulate the processes of nodulation and morphogenesis in the legume-rhizobial symbiosis [73]. It is shown that the cells of nodule bacteria during the action of exogenous polysaccharides (Baktozol) in‐ creased in growth, produced more biomass and changed the activity of some enzymes of the nitrogen exchange [74, 75]. The stimulating effect of the synthetic polysaccharide (PS MOD-19) on the growth of rhizobia, biomass accumulation and changes in their metabolism during the growth of bacteria on solid and liquid media in the presence of the biopolymer was later revealed. During the processing of the seeds of peas (*Pisum sativum* L.) prior to sowing whith PS MOD-19 there was found an increased rhizogenesis in plants, an increased peroxidase activity in plant cells, as well as the increase of the effectiveness of symbiosis as a whole due to secondary formation of nodules on side roots and the prolonging of the period of their active nitrogen fixation [76]. In this regard, synthetic polysaccharides may be of in‐ terest as biologically active compounds for practical application, in particular, for the expan‐ sion of the range of substances that can stimulate the growth activity of rhizobia and, to a greater extent, enhance and prolong the activity of nitrogen-fixing nodules formed on roots of leguminous plants. The latter circumstance is of particular importance for legumes with a short vegetation period, of which the most vivid representative is the pea [73]. In our opin‐ ion, further study of the stimulating effect of polysaccharides of different origin is a promis‐

ated on the basis of microorganisms with genetically modified properties.

genes that "sit in silence" in the uninoculated plant roots.

ing direction of improving the efficiency of legume-rhizobial symbiosis.

Our studies also show the effectiveness of biological products of nodule bacteria modified by homologous lectin, and the economic feasibility of their use [47, 49-51, 77-79]. In accord‐ ance with the existing concepts about the mechanisms of interaction of plants with rhizobia, polysaccharides of the latter are a factor which provides a "recognition" by the bacteria of the corresponding host plant through complementary binding to the plant lectin. Lectins are

based on them.

Relationships

72

The results of our studies indicate to the prospects of using bacterial agents modified by ho‐ mologous lectin, both liquid and manufactured on a solid carrier (Table 1).

The use of this protein makes it possible to improve the efficiency of the symbiotic sys‐ tem of soybean *Glycine max* (L.) Merr. and increase its productivity. The tests showed that the concentration of homologous lectin of 100 mcg / ml of bacterial suspension *Bradyrhizobi‐ um japonicum* is the optimal dose in both physiological and economical aspects in the man‐ ufacture of rhizobia preparations using perlite as a solid carrier (Table 2). In addition, the effectiveness has been established of using bacterial preparations modified by homolo‐ gous lectin, on the basis of active production-strains of rhizobia and some Tn5-mutants (T66 and T3-11) [78].


**Table 1.** Soybean seeds harvest with the application of various preparations forms of nodule bacteria with different homologous lectin concentrations (average of the 2 experiments) [80].


**Table 2.** Productivity of soybean inoculated with biological rhizobial preparation on the solid carrier (perlit) and modified with homologous lectin [80].

Note. I, II - 2005., III - 2006.

The economic efficiency of using bacterial preparations to inoculate the seeds of legume plants before sowing depends on the increase of yield, its cost and additional expenses. The calculation of economic efficiency of soybean production via a typical technological map was shown on a farm in the Kiev region (Table 3). By using bacterial preparations of soy‐ bean nodule bacteria (application of inoculation) the yield of the crop increased throughout Ukraine by an average of at least 12%, which makes it possible to increase the profitability of production to 27.8% (see Table 3). The use of bacterial preparations modified by homolo‐ gous lectin in the conditions of our field trials led to an increase in soybean yield of no less than 9.8% in comparison with conventional inoculation (see Table. 1 and 2). A comparative analysis of various indicators of economic efficiency of soybean cultivation points to the fea‐ sibility of using bacterial preparations to inoculate seeds (see Table 3). The profitability of production at the same time increased by 11.7%. The maximum profitability (39.2%) was ob‐ served when using bacterial preparations modified by homologous lectin, indicating the benefits of their use. Table 4 also shows that the use of bacterial preparations reduced pro‐ duction costs and increased net income. Thus, the cultivation of soybeans in the conditions and fields of Ukraine can produce about 0.4 hryvnia net profit to every 1 hryvnia spent. Therefore different preparatory forms of nitrogen-fixing microorganisms effectively increase the productivity of plants and can be recommended for agricultural production. The use of bacterial agents leads to a slight increase in the cost of production while the economic effect of using nitrogen-fixing bacteria is achieved due to the additional crop yield, the savings made on fertilizers and the reduction of other production energy costs.


**Table 3.** Economic effect of bacterial preparations application while producing soybean seeds (the condition of 2006), the preparations being modified with homologous lectin [80].

Note. UAH - Ukrainian hryvna.
