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Meloidogyne incognita Kofoid et White is one of the most dangerous root-knot nematodes in greenhouses. In this study, we evaluated two Bacillus strains (Bacillus velezensis BZR 86 and Bacillus velezensis BZR 277) as promising microbiological agents for protecting cucumber plants from the root-knot nematode M. incognita Kof. The morphological and cultural characteristics and enzymatic activity of the strains have been studied and the optimal conditions for its cultivation have been developed. We have shown the nematicidal activity of these strains against M. incognita. Experiments with the cucumber variety Courage were conducted under greenhouse conditions in 2016–2018. We determined the effect of plant damage with M. incognita to plants on the biometric parameters of underground and aboveground parts of cucumber plants, as well as on the gall formation index and yield. It was found that the treatment of plants with Bacillus strains contributed to an increase in the height of cucumber plants by 7.4–43.1%, an increase in leaf area by 2.7–17.8%, and an increase in root mass by 3.2–16.1% compared with the control plants without treatment. The application of these strains was proved to contribute to an increase in yield by 4.6–45.8% compared to control. Our experiments suggest that the treatment of cucumber plants with two Bacillus strains improved plant health and crop productivity in the greenhouse. B. velezensis BZR 86 and B. velezensis BZR 277 may form the basis for bionematicides to protect cucumber plants from the root-knot nematode M. incognita.

Stem canker and black scurf caused by Rhizoctonia solani are the important diseases in potato, while spur blight caused by Didymella applanata is a major disease in red raspberry. In Western Siberia, both crops are grown predominantly in small-scale farming that requires maximal usage of biological products for plant protection instead of chemicals. We evaluated two promising Bacillus velezensis strains BZR 336 g and BZR 517 isolated in the south of Russia (45°1′N, 38°59′E) for their biological control potentials against the potato and red raspberry diseases under the more severe weather conditions of Western Siberia (55°1′N, 82°55′ E). We tested two techniques to apply biocontrol agents: (1) coating the seeds (potato tubers) and (2) spraying over the plants (raspberry canes). In each case, we estimated B. velezensis strains on two plant cultivars differed by the disease resistance. The degree of B. velezensis influence on disease incidence and severity depended on the bacterial strain, the protected plant, and its cultivar. We also demonstrated that two B. velezensis strains significantly stimulated plant growth of potato, which contributed to the plant productivity on both cultivars. The BZR 336 g strain affected the potato productivity more than the BZR 517 strain. Under the influence of both bacterial strains, raspberry yield was significantly higher compared to the control on the susceptible cultivar. These findings indicated that two southern B. velezensis strains had proved their efficacy as biological control agents in the control of the serious fungal infection of potato and raspberry plants under the more severe ecological conditions of Western Siberia. For the first time, we demonstrated B. velezensis strains potential for use as biological control agents against R. solani on potato, and against D. applanata on red raspberry.

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Phytoparasitic nematodes are dangerous pests of agricultural crops. Annually, yield losses due to damage by phytonematodes are up to 15%, which is estimated at billions of dollars. The aim of the research is to summarize and analyze scientific publications concerning the harmfulness of phytoparasitic nematodes and microorganisms that have an antagonistic effect against them for the further development of biopreparations of nematicidal action based on antagonist bacteria. The study objectives are to identify the most common groups of nematodes, review the information concerning microorganisms that have a nematicidal effect and biological products based on them. The review considers the main representatives of nematodes – plant parasites and notes their habitat, harmfulness, affected crops and symptoms of infection. Brief descriptions of life cycles and systematic affiliation are given. Analysis of scientific publications on the studied topic shows that numerous microorganisms are capable of exhibiting nematicidal activity, directly or indirectly affecting nematodes in the soil. In the course of the analysis of literary sources, it was found that both fungi and bacteria can exhibit an antagonistic effect against phytoparasitic nematodes. It is noted that for both groups of microorganisms, there are several mechanisms of action: predation, parasitism, competition, etc. It has been found that fungi and bacteria synthesize metabolites of various natures with a nematicidal effect: toxins, lytic enzymes, antibiotics, siderophores. It should be noted that microorganisms-antagonist are capable of exhibiting nematicidal activity to nematodes of different stages of the life cycle: eggs, juveniles and adults. Nowadays, some commercial preparations based on antagonist microorganisms are successfully used in agriculture in different countries. During the analysis, it was discovered that to date, few viruses are capable of infecting nematodes; their systematic affiliation has also been established. It is noted that, if compared to bionematicides based on fungi and bacteria, not a single bionematicide based on viruses has been developed. The development of bionematicides based on antagonist microorganisms is a promising area but requires further studies of interactions in the plant-nematode-microorganism system.

Fungi of the genus Fusarium are economically significant pathogens in most wheat-growing regions worldwide. The biocontrol agents Bacillus velezensis BZR 336 g and BZR 517 were tested for growth inhibition of F. graminearum BZR 4. The results demonstrated that the strains are capable of deforming and destroying hyphae. The modified bioautography technique showed that the strains produce iturin A and surfactin, which probably explains the mechanism of pathogen inhibition. Furthermore, lipopeptides were detected and identified in two samples by the HPLC-HRMS. Compounds such as surfactin and their isomers and homologues were found in both samples. An experiment on an artificial infectious background in a climatic chamber established that the biological effectiveness of strains is close to that of chemical and biological references. Cultivation of plants with B. velezensis showed that the strains are likely to reduce the stress load. An efficacy of up to 45.0% was determined for bioagents BZR 336 g and BZR 517 in field trials, while the yield was up to 7.9 t/ha. The use of B. velezensis BZR 336 g and BZR 517 as biocontrol agents provides an environmentally friendly approach to the control of Fusarium rots on wheat, reduction of the pesticide load, and hence quality harvest.