Symbiotic Productivity Research Articles

ОЦЕНКА ИСХОДНОГО СЕЛЕКЦИОННОГО МАТЕРИАЛА ЛЮЦЕРНЫ

The results of the North Caucasus Research Institute of Mining and Foothill Agriculture, a branch of the Federal State Budgetary Institution of Science of the Federal Center Vladikavkaz Scientific Center of the Russian Academy of Sciences, are presented. The possibilities of selecting breeding samples with high winter hardiness, feed and seed productivity have been studied, and the analysis of the most productive samples by symbiotic productivity has been carried out. The object of research was various varieties of alfalfa of domestic and foreign breeding. A variety of clover, Kevsala, served as a control. During statistical data processing, the best samples were compared with the standard. Alfalfa varieties were also evaluated according to a set of economically valuable characteristics in order to identify hay-pasture-type varieties. The plants were sown in a wide order and individually in a row. The direct dependence of alfalfa seed formation on weather conditions is noted. On plants of the studied alfalfa varieties, the winter hardiness index is higher than the Manic standard variety (88%), the varieties Vega 87, Pasture 88, Rostovskaya 60, Uralochka, Sarga, Flora are characterized. Low level of winter hardiness (up to 80%) in varieties: Sparta, Tianshan, Peruvianskaya, Semirechenskaya, Cheshminskaya 131, Artemis, Virini, Yeruslanka. The highest rates of contamination were observed in the Kotlasky local variety – 64.9%. Also, in solving the problem of feed protein, the biological capabilities of perennial legumes are of great importance, the cultivation of which allows you to reduce the cost of nitrogen fertilizers, while obtaining high yields of good quality. Alfalfa crops annually accumulate about 150 kg/ha of nitrogen in the process of symbiosis. As shown by the analysis of the effectiveness of legume-rhizobial symbiosis, the number of active nodules exceeded the number of inactive ones in both the first and second years of life. On average, the number of active nodules on alfalfa roots in the first year of use was 160-230 pcs. /rast., in the second year of life 210-270 pcs./rast.

BIOLOGICAL NITROGEN FIXATION AS A WAY OF INCREASE YIELD OF SOY

The article highlights the importance of soybeans as one of the main agricultural crops for the life support of society with food. It is well known that soybeans have been the main high-margin crop for many global farmers, including Ukraine, in recent years. The interest in this crop continues to grow as new opportunities for its sale abroad open up, especially in such a giant country as China, the world's largest soybean importer. The right variety accounts for more than 50% of production success. It is important to identify and create optimal conditions for realising the potential nitrogen-fixing activity of soybeans of each variety in specific soil and climatic conditions. Scientists have pointed out that the main reasons that significantly limit symbiotic fixation in our conditions are relatively drier soybean cultivation conditions, especially in the face of abrupt climate change. However, it is also noted that the starting rates of nitrogen fertilisers + symbiotically fixed nitrogen can only offset part of the soybean plants' need for a yield of 4.0 t/ha. The air contains about 76% of nitrogen in the form of N2 gas, which is not available for plant nutrition. However, thanks to the unique ability of legumes to form symbiotic relationships with bacteria of the Bradyrhizobium and Rhizobium genera, N2 gas is converted into an ammonium form of nitrogen suitable for plant use. This interaction takes place in the nodules, which contain the respective bacteria. According to established data, up to 70% of the total nitrogen consumption of soybeans is obtained through biological fixation of nitrogen from the air through symbiosis with nodule bacteria. Based on the analysis of scientific publications on the symbiotic productivity of soybean crops in Ukraine and the world, the indicators of biological fixation by soybean crops in the context of the main soybean producing countries are presented and the importance of soybean cultivation in Ukraine is proved. It is confirmed that soybeans are an important strategic crop in Ukraine, which contributes to the stabilisation of agriculture, increase of soil fertility and nitrogen reserves, eliminates protein deficiency and helps to solve the food problem. The increase in gross soybean harvest is not only due to the expansion of sown areas, but also due to higher yields. To increase the efficiency of soybean production, it is proposed to introduce a set of innovative solutions at different stages of production, as well as to use new, productive varieties. In many publications, the authors emphasise that 30-35% of success in soybean cultivation depends on the right choice of variety and optimally selected technological methods of growing this crop.

Influence of biologisation of the nutrition system on the transformation of biological nitrogen and formation of soybean productivity

Rising prices for mineral fertilisers stimulate the search for alternative ways to optimise the existing and develop new technological methods of growing crops, including soybeans. One of these approaches is the intensive use of biological ways to enhance the ability of legumes to symbiosis and natural fixation of biological nitrogen from the soil air, which will help reduce the cost of plant cultivation technology. That is why the purpose of this study was to determine the effect of biological preparations on atmospheric nitrogen fixation by soybean plants using symbiotic nodule bacteria. In these studies, the method of calculation based on active symbiotic potential and symbiotic specific activity was used to determine the amount of biologically fixed nitrogen. The study analysed the effect of some inoculants and biofertilisers intended for foliar application on the development and formation of symbiotic processes in soybean plants, namely, the specific features of the formation of both general and active symbiotic potential in the vegetation stages. The influence of symbiotic productivity on soybean grain yield was also determined. Treatment of seeds with the selected preparations for the entire period of symbiosis duration provided an increase in the total symbiotic potential and active symbiotic potential. It was found that the treatment of seeds with the inoculant Bioinoculant BTU (2 l/ha) before sowing was more productive. Therewith, the maximum soybean grain yield of 3.31 t/ha was recorded in areas where the preparation Bioinoculant BTU (2 l/t) was treated before sowing and two fertilising applications were made in the 3rd ternate leaf stage and in the budding stage with Helprost soybean fertiliser (2.5 l/ha). The findings of this study indicate a substantial impact of symbiotic productivity and its value on soybean grain yield. Correlation and regression analyses showed that the accumulation of biological nitrogen has a considerable impact on grain yield. Thus, the use of biological preparations is an alternative to mineral fertilisers in soybean cultivation technology and they can be implemented in the production conditions of agricultural enterprises

Symbiotic productivity of soybeans depending on inoculation and fertiliser in conditions of the Right-Bank Forest-Steppe

Given the high value of the biochemical composition of soybean seeds and the versatility of using this crop, the need for it will continue to grow, which makes it necessary to improve existing and develop new technologies for its cultivation, considering local agroclimatic resources. Therefore, this study, aiming to investigate the agroecological foundations of the use of chemical and biological techniques in modern technologies for growing soybeans, is relevant. The purpose of the study was to identify the features of the formation of symbiotic productivity of soybeans under the influence of bacterial and mineral fertiliser in the conditions of the Right-Bank Forest-Steppe of Ukraine. A field method was laid down according to the developed scheme to achieve this goal. The positive effect of mineral fertiliser and inoculation on the formation of the symbiotic apparatus of soy and its productivity was established. The smallest increase in the number of root nodules was noted for the introduction of N45P60K60 – 24.7-27.3%, depending on the variety. Small initial doses of nitrogen were more effective – within the limits of N15–30 – they provided an increase in the number of active bulbs by 51.2-106.9%. Bacterisation of seeds with the complex bacterial preparation Phosphonitragine increased the number of active nodules on soybean roots by 106.8-138.6%, depending on the variety. The interaction of technological methods of mineral fertilisation and inoculation contributed to an increase in both the number of nodules with leghemoglobin – by 128.5-198.6%, and their mass – by 111.1-147.6%. The soy symbiotic apparatus was maximally developed by interacting seed inoculation factors with a bacterial preparation containing Br. japonicum and B. Mucilaginosus strains and applying N30P60K60 +N15 in the budding phase. This technological model of crop cultivation provided the highest productivity of legume-rhizobial symbiosis of soybean plants in terms of the volume of accumulation of symbiotically fixed nitrogen – in the early-ripening soybean variety Vilshanka – 124.2 kg/ha, in the medium-ripening variety Suziriia – 130.3 kg/ha. The practical importance of the obtained results is in the improvement of varietal technologies for growing soybeans based on the complex application of seed inoculation with a bacterial preparation and the introduction of nitrogen fertilisers in retail against the background of phosphorus-potassium fertiliser

Biological nitrogen in increasing the productivity of beans (grains)

The results of a field experiment to study the effect of seed treatment with the biological product Rhizoactive (сompany BioNorma, Ukraine) on the formation and functioning of the symbiotic apparatus of common bean (grain) plants are presented.
 The experiment examined six varieties of common beans (grain), included in the State Register of plant varieties suitable for distribution in Ukraine: Bukovynka, Halaktyka, Slaviia, Ros, Otrada, Nata. The influence of bacterial fertilizer based on nodule bacteria " Rhizoactive " on the indicators of symbiotic and grain productivity of these varieties of common beans was studied.
 It was found, that the maximum number and raw weight of active nodules in the studied varieties of common beans were formed in the flowering phase. A larger number of nodules, compared to the variety Bukovynka (control), was formed on the root system of bean varieties Ros, Otrada and Nata. The maximum raw weight of rhizobia in the plots without the use of Rhizoactive was formed by the common bean variety Otrada – 0.297 g/plant of active nodules. Inoculation of the seeds of the studied common bean varieties with Rhizoactive increased the raw weight of active nodules in the flowering phase by 0.016–0.042 g/plant. A larger mass of nodules, compared to the Bukovynka variety, was formed on the root system of Ros, Otrada and Nata beans. The maximum raw weight of rhizobia in areas without the use of Rhizoactive was formed by the variety of beans Otrada – 0.297 g/plant of active nodules. Inoculation of seeds of the studied varieties of beans with Rhizoactive increased the raw weight of active nodules in the flowering phase by 0.016–0.042 g/plant.
 The highest increase in grain yield from seed inoculation was obtained in 2018, which was more favorable in terms of moisture. Thus, the largest increase in grain yield from the use of Rhizoactive was provided by the varieties Halaktyka (0.14 t/ha or 5.7 %), Ros (0.15 t/ha or 5.5 %) and Otrada (0.22 t/ha or 7.7 %). On average, in 2018–2020, inoculation of bean seeds with Rhizoactive, depending on the variety, provided an increase in grain yield from 2.4 to 6.7 %. And the highest level of bean grain yield on average in 2018–2020 was provided by the varieties Otrada (2.60 t/ha), Nata (2.50 t/ha) and Ros (2.40 t/ha) for inoculation of seeds with Rhizoactive

Вплив технологічних заходів вирощування на розвиток кореневої системи та симбіотичну продуктивність еспарцету

An important factor in the feed industry intensification is the cultivation of perennial legumes, including sainfoin. The aim of the study was to determine the effect of mineral fertilizers and seed inoculation on the formation of the root system and the symbiotic productivity of different varieties of sainfoin grown on green fodder. Experimental studies were conducted during 2016-2018 on the research field of Forage Production, Land Reclamation and Meteorology Department, located at the NULES of Ukraine "Agronomic Research Station" on typical low-humus chernozem. According to the results of the research, it was established that on average in three years the biggest root mass - at the level of 52.7 t/ha was formed by sainfoin variety Amethyst Donetskyi with providing complete mineral fertilizer in the dose N45P60K90 and presowing seeds inoculation by Rhizotorphin. In plants of the same variant, the most developed symbiotic apparatus was also noted - in the flowering phase, the total number of tubers was 126 units/plant, and their weight was 3.444 g/plant. As a result of a strong root system of plants formation and a well-developed symbiotic apparatus, the amount of biologically fixed nitrogen under crops of sainfoin of variety Amethyst Donetskyi reached 143 kg/ha.

Sinorhizobium medicae WSM419 Genes That Improve Symbiosis between Sinorhizobium meliloti Rm1021 and Medicago truncatula Jemalong A17 and in Other Symbiosis Systems.

Some soil bacteria, called rhizobia, can interact symbiotically with legumes, in which they form nodules on the plant roots, where they can reduce atmospheric dinitrogen to ammonia, a form of nitrogen that can be used by growing plants. Rhizobium-plant combinations can differ in how successful this symbiosis is: for example, Sinorhizobium meliloti Rm1021 forms a relatively ineffective symbiosis with Medicago truncatula Jemalong A17, but Sinorhizobium medicae WSM419 is able to support more vigorous plant growth. Using proteomic data from free-living and symbiotic S. medicae WSM419, we previously identified a subset of proteins that were not closely related to any S. meliloti Rm1021 proteins and speculated that adding one or more of these proteins to S. meliloti Rm1021 would increase its effectiveness on M. truncatula A17. Three genes, Smed_3503, Smed_5985, and Smed_6456, were cloned into S. meliloti Rm1021 downstream of the E. coli lacZ promoter. Strains with these genes increased nodulation and improved plant growth, individually and in combination with one another. Smed_3503, renamed iseA (increased symbiotic effectiveness), had the largest impact, increasing M. truncatula biomass by 61%. iseA homologs were present in all currently sequenced S. medicae strains but were infrequent in other Sinorhizobium isolates. Rhizobium leguminosarum bv. viciae 3841 containing iseA led to more nodules on pea and lentil. Split-root experiments with M. truncatula A17 indicated that S. meliloti Rm1021 carrying the S. medicae iseA is less sensitive to plant-induced resistance to rhizobial infection, suggesting an interaction with the plant's regulation of nodule formation. IMPORTANCE Legume symbiosis with rhizobia is highly specific. Rhizobia that can nodulate and fix nitrogen on one legume species are often unable to associate with a different species. The interaction can be more subtle. Symbiotically enhanced growth of the host plant can differ substantially when nodules are formed by different rhizobial isolates of a species, much like disease severity can differ when conspecific isolates of pathogenic bacteria infect different cultivars. Much is known about bacterial genes essential for a productive symbiosis, but less is understood about genes that marginally improve performance. We used a proteomic strategy to identify Sinorhizobium genes that contribute to plant growth differences that are seen when two different strains nodulate M. truncatula A17. These genes could also alter the symbiosis between R. leguminosarum bv. viciae 3841 and pea or lentil, suggesting that this approach identifies new genes that may more generally contribute to symbiotic productivity.

Symbiotic productivity and yield of seeds of soybean depending on inoculation and fertilizing

Symbiotic productivity and yield of seeds of soybean depending on inoculation and fertilizing

Symbiotic activity and productivity of soybeans depending on the use of phosphorus fertilizers

Symbiotic activity and productivity of soybeans depending on the use of phosphorus fertilizers

ПРИЕМЫ ПОВЫШЕНИЯ ЭФФЕКТИВНОСТИ РАБОТЫ СИМБИОТИЧЕСКОГО АППАРАТА НУТА ПРИ ВЫРАЩИВАНИИ В СТЕПНОЙ ЗОНЕ ПОВОЛЖЬЯ

The results of the period 2011-2016 are presented. field experiments to improve the technology of cultivation of chickpea in the steppe zone of the Volga region. The purpose of the research was to improve the methods of increasing the efficiency of the symbiotic apparatus of chickpea when grown in the steppe zone of the Volga region. The climate of the research zone is arid. The soil of the experimental field of the Saratov State Agrarian University is southern medium loamy chernozem containing 3.5-4.0% of humus in the arable horizon. The soil of the experimental field of the Krasnokutsk SOS is chestnut, heavy loamy with a content of 2.8-3.0% of humus in the arable horizon. In the studies carried out, a different effect of mineral fertilizers, biological products and growth stimulants on the symbiotic process in chickpea crops and the provision of plants with biological nitrogen was revealed. The highest symbiotic productivity was distinguished by agrocenoses created with the use of a specialized bacterial preparation, rhizotorfin, in the pre-sowing treatment of chickpea seeds. At the same time, on the chernozems of the southern steppe zone of the Volga region, the highest indicators in the number and weight of nodules were noted when using rhizotorfin against the second background of mineral nutrition, where phosphorus fertilizers were used at a dose of P30 - 31.5 pcs. and 318.4 mg. per 1 plant in the chickpea flowering phase. On the chestnut soils of the steppe zone of the Volga region, in order to increase the symbiotic nitrogen fixation of chickpea, it is necessary to jointly use rhizotorfin for pre-sowing seed treatment and to apply mineral fertilizers at a dose of N20P30 before sowing - against this background, on the roots of one chickpea plant in the flowering phase, the largest number and the highest mass of nodules were formed - respectively 33 , 8 pcs. and 140.7 g. Assessment of the safety of the symbiotic potential by the middle of the phase of bean formation in comparison with the flowering phase made it possible to reveal that if 58.8% of live nodules and 40.9% of the treatment of seeds and crops of chickpea preserved respectively 75.5 and 80.4 %% of live nodules and 56.8 and 60.6% of the mass of nodules. As a result of the studies, it was found that the use of siliplant microfertilizer-stimulator and zircon growth stimulator contributes to a longer work of the active symbiotic apparatus of chickpea. In general, the studies have shown that in the region of the arid steppe Volga region, where the level of productivity of agricultural crops, the use of biological products and growth stimulants at a low cost of their use should be widely used in modern resource-saving cultivation technologies.

Effect of diverse nutrient application on symbiotic traits, yield attributes, nutrient uptake, microbial population, dehydrogenase activity and productivity of chickpea (Cicer arietinum L.) in black Soils

Field experiments conducted in black soils, having low organic carbon and available N, medium P, high K and extractable molybdenum below the critical limit (less than 0.2ppm), to assess the effect of fertilizers, vermicompost (VC), amritpani (AP), biofertilizers inoculation (BFSI) viz., Rhizobium + Phosphorus solublizing bacteria + Plant growth promoting rhizobacteria with molybdenum application on chickpea (Cicer arietinum L.). Eight treatments viz. T1- Control (Recommended dose of fertilizers (RDF), T2- RDF + Ammonium molybdate (AM) @ 1 g kg-1 seed with BFSI, T3- Spray of AP at 30 and 60 DAS + AM @ 1 g kg-1 seed with BFSI, T4- VC @ 2 t ha-1 + AM @ 1 g kg-1 seed with BFSI, T5 -AP spray at 30 and 60 DAS + VC@ 2 t ha-1 + AM @ 1 g kg-1 seed with BFSI, treatments: T6, T7 and T8 consisted of 50% RDF with T3, T4 and T5 respectively, were tried in RBD. Nodulation, plant height, branches plant-1, number of pods plant-1, seed index, chlorophyll content and Uptake of NPK recorded significantly higher with T2,T6,T7 and T8 over T1 with maximum under T8 (50% RDF + T4) followed by with T7. As regards the grain yield, treatments T7, T8 and T2 resulted in significant yield increase by 27.5, 28.2 and 25.6% over RDF alone (1692 kg ha-1). Actinomycetes, Fungi and DHA recorded higher in soil wherever organics (vermicompost) and bio fertilizers inoculation was done. Available NPK in soil after crop harvest was recorded better with the integrated nutrient inputs.

Symbiotic parameters, growth, nutrient accumulation, productivity and profitability as influenced by integrated nutrient management in lentil (Lens culinaris)

ABSTRACTField experiments evaluated the effects of integrated nutrient management on symbiotic parameters, growth, nutrient accumulation, productivity and profitability of lentil (Lens culinaris Medikus). Application of recommended dose of nutrients (RDN, 12.5 kg N ha−1 + 40 kg P2O5 ha−1) + 25 kg ZnSO4 ha−1 + seed inoculation with biofertilizers [Rhizobium + phosphate solubilizing bacteria (PSB) + plant growth promoting rhizobacteria (PGPR)] + 1.0 g ammonium molybdate kg−1 seed recorded the highest number & dry weight of nodules, leghaemoglobin content, root & shoot dry weight, plant height, number of pods plant−1 and 100-seed weight. The next best treatment was RDN + seed inoculation with biofertilizers + 1.0 g ammonium molybdate kg−1 seed. On the basis of mean of three-year data, the treatment of RDN + 25 kg ZnSO4 ha−1 + seed inoculation with biofertilizers + 1.0 g ammonium molybdate kg−1 seed proved the best in realizing the highest grain yield (34.0%), gross returns (34.0%) and net returns (54.8% higher over control). Nitrogen, phosphorus and potassium in the grains and straw were significantly improved where RDN was applied in combination with seed inoculation, basal application of ZnSO4 and seed treatment with 1 g ammonium molybdate than their single applications.

Симбіотична продуктивність сої залежно від інокуляції насіння та удобрення

Симбіотична продуктивність сої залежно від інокуляції насіння та удобрення

FUNCTIONING OF NITROGEN FIXATION SYMBIOSIS AND PEAS PRODUCTIVITY UNDER THE APPLICATION OF DIFFERENT TYPES AND DOSES OF FERTILIZERS

The efficiency of different types and doses of fertilizers and pre-sowing bacterization of pea seeds (Starter variety) on the formation and functioning of symbiotic nitrogen fixation system, crop productivity and protein content in grain was studied in long-term field experiment on the typical black soil for five years. It was shown that fertilizer doses not exceeding N60P60K60 were the most appropriate to use in the cultivation technology of pea. The use of manure, compost and organic-mineral fertilizer in crop rotation had positively affected the productivity of peas. Pre-sowing seed bacterization was proved to be an important agricultural practice as its application increases crop productivity and improves product quality.

ПРОДУКТИВНОСТЬ И КЛУБЕНЬКООБРАЗУЮЩАЯ СПОСОБНОСТЬ У СОРТОВ ФАСОЛИ ОБЫКНОВЕННОЙВ УСЛОВИЯХ ПРЕДУРАЛЬЯ

Common bean ( Phaseolus vulgaris L.) has a high nutritional value, its seeds contain a significant amount of protein and essential amino acids and vitamins. Furthermore, it can accumulate organic nitrogen in the soil due to nitrogen fixation. On the territory of the forest-steppe zone of Urals (Bashkortostan) in small plot experiments in homogeneous soil conditions during five years the elements of yield structure of four cultivars of common bean (Gornal, Ufimskaya, Zolotistaya and Elsa) were studied. In different soil and climatic conditions the distribution character (skewness) of seed production and nodule activity were compared. Сorrelations between agro-meteorological factors, nodules number and productivity were determined. In one of these experiments there were watering and using of start doses of fertilizers (PK) 45. The remaining experiments were carried out in a natural agricultural background without irrigation. The seeds yield of local cultivars (Gornal, Ufimskaya, Zolotiataya) in homogeneous soil conditions on leached chernozem (Ufa district) ranged from 18 to 22 kg/ha. High seed productivity of a new cultivar Elsa was mentioned. In the experiments without irrigation (Ufa, Iglinskiy, Chishminskiy, Bakalinskiy areas) the seed weight of different cultivars changed depending on the agro-meteorological conditions from 4 to 17 g/plant, being doubled at watering. An average rang of seed production variation for all years was 50 % for Zolotistaya cultivar, 53 % for Elsa, 57 % for Ufimskaya and 76 % for Gornal cultivars. The close relationship ( r = 0.61) between the productivity of beans and the sum of active temperatures above 15 °С was revealed. Greater flexibility to the amount of heat was shown in the locally bred varieties Zolotistaya and Ufimskaya at r = 0.46 and r = 0.59, respectively, greater dependence on abiotic factors was demonstrated by Gornal and Elsa varieties at r = 0.78 and r = 0.84, respectively. Similar relations were revealed when the analysis of correlative links was made between the duration of the period of above 15 °С temperatures and the seed productivity. Thus, correlation was detected at r = 0.42 and r = 0.20 for Zolotistaya and Ufimskaya cultivars, and at r = 0.51 and r = 0.69, for Gornal and Elsa, respectively. In different conditions there were from 5 to 29 nodules formed at a plant. The average variation of nodule activity between all cultivars during all years was 15.3 %. However, for each cultivar under different soil and climatic conditions the individual average coefficients of variation differed, being 44 % for Gornal, 59 % for Zolotistaya, 65 % for Ufimskaya and 18 % for Elza varieties. In most experiments the positive skewness prevailed in both the number of nodules and productivity. Normal distribution and the negative skewness for all cultivars were observed in the experiment with watering, and occurred more frequently in plants of Zolotistaya cultivar. Number of nodules per plant and seed production correlated ( r = 0.75-0.87) only under optimal water regime and mineral nutrition. On the gray forest soil the plants formed a symbiosis with local rhizobia, and on the chernozem soil the symbiotrophic nitrogen nutrition prevailed over mineral nitrogen one. The revealed high intravarietal variability of common bean plants and the asymmetric distribution of symbiotic activity and productivity suggest the possibility for selecting lines to improve the efficiency of symbiosis. A randomly formed supernodulating hybrid L20 of cultivar Elza was discovered to be promising for further breeding.

The Succinoglycan Endoglycanase Encoded by exoK Is Required for Efficient Symbiosis of Sinorhizobium meliloti 1021 with the Host Plants Medicago truncatula and Medicago sativa (Alfalfa)

The acidic polysaccharide succinoglycan produced by the nitrogen-fixing rhizobial symbiont Sinorhizobium meliloti 1021 is required for this bacterium to invade the host plant Medicago truncatula and to efficiently invade the host plant M. sativa (alfalfa). The β-glucanase enzyme encoded by exoK has previously been demonstrated to cleave succinoglycan and participate in producing the low molecular weight form of this polysaccharide. Here, we show that exoK is required for efficient S. meliloti invasion of both M. truncatula and alfalfa. Deletion mutants of exoK have a substantial reduction in symbiotic productivity on both of these plant hosts. Insertion mutants of exoK have an even less productive symbiosis than the deletion mutants with the host M. truncatula that is caused by a secondary effect of the insertion itself, and may be due to a polar effect on the expression of the downstream exoLAMON genes.

Increased Production of the Exopolysaccharide Succinoglycan Enhances Sinorhizobium meliloti 1021 Symbiosis with the Host Plant Medicago truncatula

The nitrogen-fixing rhizobial symbiont Sinorhizobium meliloti 1021 produces acidic symbiotic exopolysaccharides that enable it to initiate and maintain infection thread formation on host legume plants. The exopolysaccharide that is most efficient in mediating this process is succinoglycan (exopolysaccharide I [EPSI]), a polysaccharide composed of octasaccharide repeating units of 1 galactose and 7 glucose residues, modified with succinyl, acetyl, and pyruvyl substituents. Previous studies had shown that S. meliloti 1021 mutants that produce increased levels of succinoglycan, such as exoR mutants, are defective in symbiosis with host plants, leading to the hypothesis that high levels of succinoglycan production might be detrimental to symbiotic development. This study demonstrates that increased succinoglycan production itself is not detrimental to symbiotic development and, in fact, enhances the symbiotic productivity of S. meliloti 1021 with the host plant Medicago truncatula cv. Jemalong A17. Increased succinoglycan production was engineered by overexpression of the exoY gene, which encodes the enzyme responsible for the first step in succinoglycan biosynthesis. These results suggest that the level of symbiotic exopolysaccharide produced by a rhizobial species is one of the factors involved in optimizing the interaction with plant hosts.

A mutant GlnD nitrogen sensor protein leads to a nitrogen-fixing but ineffective Sinorhizobium meliloti symbiosis with alfalfa

The nitrogen-fixing symbiosis between rhizobia and legume plants is a model of coevolved nutritional complementation. The plants reduce atmospheric CO(2) by photosynthesis and provide carbon compounds to symbiotically associated bacteria; the rhizobia use these compounds to reduce (fix) atmospheric N(2) to ammonia, a form of nitrogen the plants can use. A key feature of symbiotic N(2) fixation is that N(2) fixation is uncoupled from bacterial nitrogen stress metabolism so that the rhizobia generate "excess" ammonia and release this ammonia to the plant. In the symbiosis between Sinorhizobium meliloti and alfalfa, mutations in GlnD, the major bacterial nitrogen stress response sensor protein, led to a symbiosis in which nitrogen was fixed (Fix(+)) but was not effective (Eff(-)) in substantially increasing plant growth. Fixed (15)N(2) was transported to the shoots, but most fixed (15)N was not present in the plant after 24 h. Analysis of free-living S. meliloti strains with mutations in genes related to nitrogen stress response regulation (glnD, glnB, ntrC, and ntrA) showed that catabolism of various nitrogen-containing compounds depended on the NtrC and GlnD components of the nitrogen stress response cascade. However, only mutants of GlnD with an amino terminal deletion had the unusual Fix(+)Eff(-) symbiotic phenotype, and the data suggest that these glnD mutants export fixed nitrogen in a form that the plants cannot use. These results indicate that bacterial nitrogen stress regulation is important to symbiotic productivity and suggest that GlnD may act in a novel way to influence symbiotic behavior.

Productivity of soybean-rhizobium symbiosis after modification of root nodule bacteria activity with exogenous proteins

Plant growth experiments were conducted to assess symbiotic efficiency, photosynthetic rates, and the development of soybean (Glycine max (L.) Merrill) seedlings after seed inoculation with active and inactive strains of root nodule bacteria Bradyrhizobium japonicum preincubated in the presence homologous and heterologous proteins. The properties of active and inactive symbiotic strains were differentially modulated by homologous soybean lectin, which had a marked influence on plant physiological condition. The incubation of active rhizobia with a homologous lectin, i.e., lectin of the respective plant, increased the nitrogen-fixing activity of nodules and, consequently, elevated photosynthetic rates and weight increments in soybean plants. At the same time, the homologous lectin suppressed the symbiotic properties of inactive strain of nodule bacteria. The preincubation of rhizobia with a heterologous pea lectin had virtually no effect on functioning of symbiotic apparatus and photosynthetic rate, whereas the preincubation of root nodule bacteria with human albumin exerted an effect similar to that induced by a homologous lectin on symbiotic productivity.

THE EFFICIENCY OF NITRAGIN AND PLANT GROWTH REGULATORS USE IN SOYBEAN GROWING

The іnoculation and plant growth regulators have been studied for their effect on the symbiotic nitrogen fixation and productivity of soybean in the field experiments. It was shown that nitraginisation with the high efficient strain B. japonicum 71т (UCМ В-6035) promotes active rhizobium-soybean nodulation system, and crude protein yield increasing as the result of the symbiosis efficiency. The combined use of Nitragin and plant growth regulators requires attention to both cultivar peculiarities of macrosymbionts and specific action of these preparations.