Efficient plant-growth-promoting rhizobacteria (PGPR) used as biofertilizers and biological control agents are promising substitutes for minimizing the application of synthetic agrochemicals in crop production. We studied the effect of PGPR strain Bacillus velezensis BS89 alone and in combination with three forms of nitrogen fertilizers (ammonium nitrate, carbamide, and ammonium sulfate) on the productivity of two strawberry varieties in three-year field experiments. We first showed that the application of PGPR Bacillus velezensis BS89 on strawberries demonstrated the same effect as the application of nitrogen fertilizers. Use of the strain BS89 increased the chlorophyll content in plant leaves by 2.7–6.8%, and also increased the yield of berries by 6.7–36.4% for cv. Rusich and 7.5–19.3% for cv. Troitskaya depending on the form of nitrogen fertilizer. The best results in the yield of strawberry plants of the cv. Rusich were achieved in the variant BS89 + ammonium nitrate (41.9–57.4%), and the cv. Troitskaya—in the BS89 + carbamide variant (8.1–38.8%). Three-year use of strain BS89 for cv. Rusich resulted in an increase of runner’s weight by 212.1%, and also the weight of the roots by 120%, thereby significantly improving the mineral nutrition of plants. This is mainly associated with the plant growth-promoting activity of Bacillus velezensis BS89, which was able to produce a high amount of IAA—494.1 µg/mL. We believe that the PGPR strain BS89 can be successfully used for growing strawberries. However, each variety requires careful selection of the composition of nitrogen fertilizers and analysis of the compatibility of fertilizers and the PGPR strain.

In a vegetation experiment, the effect of bacterial preparations Extrasol, Fitosporin-M based on bacterial strains Bacillus subtilis and bacteria strains of the genus Pseudomonas – P. chlororaphis OV17, P. protegens 38a, P. putida О9-10 on the number of rhizosphere microorganisms, growth and development of regenerant plants of apple clone rootstocks in ex vitro conditions was studied. After 90 days of growing plants, the greatest number was found in the P. protegens 38a strain – 0.56 million CFU/g roots. Artificial inoculation of the roots of regenerant plants contributed to a significant increase in the total number of native microorganisms as compared to the control. The most diverse bacterial population in terms of cultural and morphological characteristics was revealed in the variant with the treatment of plants with the P. putida O9-10 strain. The introduced bacterial strains contributed to an increase in the adaptive capacity and had a phytostimulating effect on the development of plants. The plant survival rate in the process of adaptation to ex vitro conditions is most influenced by the P. putida 09-10 strain compared to the control. The bacterial preparation Fitosporin-M contributes to the improvement of biometric parameters of plant growth.

The paper analyzes the adaptive abilities of black currant cultivars of plants for the assimilation of nickel from highly cultivated sod-podzolic soils containing 10.7-14.1 mg / kg of fluent nickel. Plantings were monitored at experimental plantings of ARHIBAN (Moscow region) on 9 black currant cultivars: Oryol Serenade, Belarusskaja sladkaja, Zagadka, Vologda, Triton, Biryulevskaya, Titania, Orlowsky waltz, Exotica. The agrochemical properties of the soil, the content of fluent nickel in the soil, and its content in the fruits of black currant plants were determined. Based on the analysis, the coefficients of nickel assimilation by black currant plants were calculated and statistical dependencies of its accumulation indicators on agrochemical properties of sod-podzolic soils at different depths of the root layer were determined. According to the results of research, regression dependences of the accumulation of nickel in black currant fruits on the indicators of the agrochemical properties of the soil and the content in the soil of fluent nickel were constructed. It was established that the nickel content in black currant fruits primarily depended on the acidity of the soil, on the content in the soil of fluent nickel, alkaline hydrolysable nitrogen and fluent potassium. Black currant cultivars Belarusskaja sladkaja, Vologda, Triton, Biryulevskaya, Titania were more resistant to soil pollution with nickel.

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In a vegetative experiment, the effect of two concentrations of Ni in the soil of 80 and 240 mg Ni / kg on the vegetative and generative productivity of plants of three varieties of strawberries Honeoye, Troitskaya, Red Gontlet was studied. Ni soil contamination had a significant impact on the vegetative and generative productivity of strawberry plants. The degree and direction of this effect was largely dependent on the variety. When the Ni content in the soil was 80 mg / kg in plants of strawberry varieties Honeoye and Red Gauntlet, there was a tendency to an increase in leaf mass, most of all in the Honeoye variety – by 16.6 % compared to an uncontaminated fertilized background. When the Ni concentration in the soil was 240 mg / kg in Honeoye plants, the leaf mass decreased by 19.0 % relative to the uncontaminated background, while in the Troitskaya and Red Gauntlet plants, the leaf mass increased, to a maximum, in Red Gontlet plants by 57.9 %. In plants of the strawberries varieties Honeoye mass of strawberries runners when soil is polluted, Ni was decreased to the greatest extent when the content of Ni in soil is 80 mg/kg – 23.3 % relative to the background values, the varieties Troitskaya and Red Gauntlet mass of strawberries runners, it became higher, especially when the content of Ni in soil is 240 mg/kg – 24.5 % and 42.5 % of the relatively polluted background, respectively. In plants of the Honeoye variety, the number of rosettes with Ni soil contamination tended to decrease relative to the background value (maximum, by 27.0 % when the Ni content in the soil is 80 mg / kg), in the Troitskaya variety – to increase (to the greatest extent, when the Ni content in the soil is 240 mg/kg – by 220 %). In plants of the Red Gauntlet variety, the number of rosettes per plant at each of the studied levels of soil contamination with Nickel tended to decrease (by a maximum of 11.8 % with a Ni content of 80 mg/kg in the soil). The number of peduncle in plants of strawberry varieties Honeoye and Troitskaya on polluted soil tended to decrease in comparison with the background. In plants, varieties of Red Gauntlet for this parameter was an opposite trend in the contamination of soil Ni number of peduncle per plant increased relatively polluted background (maximum 60.0 % when the contamination level of 240 mg/kg). The mass of berries on one plant of Red Gauntlet strawberry with Ni soil contamination at the level of 240 mg / kg statistically significantly increased by 38.3 % relative to the non-polluted background. In plants of the Honey and Troitsky varieties, the berries mass on one plant naturally decreased compared to the non-polluted background (by 10.2 % at a Ni content of 240 mg/kg and by 44.0 % at a Ni content of 80 mg/kg, respectively). When the soil was contaminated with Ni 240 mg / kg of Red Gauntlet strawberry plants, the number of berries per plant increased by 45.3 % relative to the non-polluted background. In plants of the Honeoye and Troitskaya varieties, the number of berries per plant decreased in comparison with the non-polluted background, to the greatest extent, by 30.9 % at a content of Ni 240 mg/kg and by 29.9 % at a content of Ni 80 mg/kg, respectively.

In vegetative experiment has been studied the infl uence of adsorbents on the basis of mineral and polymer substrates Bentonite, Arpolit, Supradit, Agronit on the accumulation of heavy metals (HM) of strawberry plants plant variety Troitskaya in the artificial contamination of sod-podzolic soil at the level MAC (maximum allowable concentration) of total content of TM: Cd 2 mg/kg, Cr 100 mg/kg (MAC missing), Pb 130 mg/kg, Zn 220 mg/ kg. It was found that the use of adsorbents based on mineral and polymer substrates helps to reduce the content of mobile forms of Cr, Cd, Pb in the soil. Their content is reduced to the greatest extent when the adsorbents Supradit M are added to the soil (by 78.5 % for Cd and 40.1 % for Pb, compared with the control) and Agronite (by 79.0 % for Cd and 48.9 % for Pb, compared with the control). For mobile Cr, the downward trend in soil content was statistically unreliable. The content of mobile Zn in the variants with all adsorbents, on the contrary, increased in comparison with the contaminated control, to the greatest extent when the adsorbent Supradit M was added – by 26.1 %, compared with the control. The use of adsorbents led to a decrease in the content of Cd and Pb in the roots of strawberry plants. The greatest decrease in their content in the roots was when adding adsorbents Supradit M (65.2 % for cadmium and 76.8 % for lead, compared with the control) and Agronite (65.7 % for cadmium and 78.2 % for lead, compared with the control). The content of Zn in the roots in the variants with the introduction of adsorbents, except for Bentonite, increased in comparison with the contaminated control, to the greatest extent with the introduction of the adsorbent Supradit M – by 45.2 %. The content of Cr in the roots when using all adsorbents, except Agronite, also tended to increase, to the greatest extent when applying Arpolite – by 105.9 %, compared with the control. When applying the adsorbents Supradit M and Agronit to the soil, the content of Cd in the leaves decreased: when applying the adsorbent Supradit M by 52.9 %, Agronit – by 41.2 %, compared to the control. The content of Zn, Cr, and Pb in the leaves in the variants with adsorbents increased in comparison with the contaminated control, to the greatest extent when adding the adsorbent Arpolite: by 63.7 % – for Zn, by 71.2 % – for Cr, and by 46.3 % – for Pb. When using this adsorbent, the content of Cd in the leaves also increased – by 105.9 % higher than the contaminated control. The content of Cd, Cr, Pb, Zn in the berries of strawberry when using adsorbents less than in the roots and leaves, depended on the content of the corresponding heavy metals in the soil and was not statistically significant. When adding the adsorbents Supradit M and Agronit to the soil, the content of Cd in berries tended to decrease: when using the adsorbent Supradit M – by 30.0 %, Agronit – by 40.0 %, compared with the control. When adding the adsorbent Arpolite to the soil, the Cd content in berries tended to increase by 30.0 %, Pb – by 111.8 % from the control. The Cr content in the berries in the variants with adsorbents increased in comparison with the contaminated control, to the greatest extent with the introduction of Bentonite adsorbent – by 180.0 %. For the content of Zn in berries, there was no pronounced natural tendency for adsorbents to act. The closest relationship between the content of TM in the organs of strawberry plants and the content of mobile forms of heavy metals in the soil was observed for roots and leaves. There was no such dependency for Cr. At the studied levels of mobile TM content in the soil, the barrier properties of strawberry plants play an important role in the accumulation of heavy metals. The translocation coefficients of heavy metals were higher in the experiment variants, in which a decrease in the content of mobile forms of TM in the soil was observed when adding adsorbents. For Cd in the variant using the adsorbents Supradit M and Agronit, the TM translocation coefficients were higher than the control value by 98.0 and 72.5 %, respectively. For Pb, the values of translocation coefficients increased with the use of these adsorbents, compared to the control, by 300 % and 350 %, respectively. With an increased content of mobile forms of TM in the soil in the variants with the introduction of adsorbents Supradit M and Agronit, the translocation coefficients for Zn, compared to the control, were lower by 33.3 % and 33.3 %, respectively.

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