Biological effectiveness of soil actinobacteria for growing Cucumis sativus L. in greenhouses

Chemical pesticides are used to control viral and fungal plant diseases and insect pests, but due to multiple treatments, the resistance of pathogens to them increases. Biopesticides serve as an alternative to chemical pesticides. The use of actinobacteria strains is promising for the development of new biologicals with antiviral, fungicidal and insecticidal effects. In this work, the effectiveness of actinobacterium Nocardiopsis umidischolae RCAM04882, N. umidischolae RCAM04883, Streptomyces carpaticus RCAM04697 in growing cucumber plants in greenhouses under the arid climate of the south of the Russian Federation were shown for the first time. Our goals was to investigate the effect of three strains of soil actinobacteria on cucumber ( Cucumis sativus L.) cv. Forvard yield and the incidence of fungal and viral diseases and attacks of insect pests in a greenhouse (Astrakhan Province, 2019).. The plants were inoculated with 3-day cultures of the actinobacteria and suspensions of their dry biomass diluted in sterile distilled water to 1 mg/1 ml. N. umidischolae RCAM04882, N. umidischolae RCAM04883, Streptomyces carpaticus RCAM04697 strains (109 CFU/ml) were isolated from saline soils in the Astrakhan region in 2013. Tests were carried out under natural infectious loads. Root watering was applied 1 day after planting 2-3 true leaves’ seedling, 8 days after the first treatment during plant active growth, 8 days after the second treatment at budding and flowering. Then the plants were sprayed 14 days after the third treatment at ovary formation and milk ripeness, 14 days after the fourth treatment during active fruiting, and 14 days after the fifth treatment at harvesting. The treatments were as follows: 1 - positive control (treatment with the reference biological preparation Phytosporin-M (PS), paste) (NVP BashInkom LLC, Russia); 2 - negative control (treatment with tap water); 3 - treatment with suspension of N. umidischolae RCAM04882; 4 - treatment with suspension of N. umidischolae RCAM04883; 5 - treatment with suspension of S. carpaticus RCAM04697; 6 - treatment with suspension from dry biomass of strain N. umidischolae RCAM04882; 7 - treatment with suspension from dry biomass of strain N. umidischolae RCAM04883; 8 - treatment with suspension of dry S. carpaticus RCAM04697 biomass. The precursors of cucumber plants were tomatoes ( Solanum lycopersicum ) of the Grand variety. The soil was disinfected with copper sulfate before planting seedlings. The watering was carried out by drip method with a rate of 4.5-5 l per plant with tap water heated to 26 °С. Harvesting began on June 1, with the last harvest date being August 31. The insecticidal activity of actinobacteria strains against the melon aphid Aphis gossypii and the spider mite Tetranychus urticae was recorded on days 3 after the third and fourth treatments. The viral infections was detected by serological method at the stage of ovary formation (3 days after the third treatment) and fruit ripening (3 days after the fourth treatment). For immunochemical detection of viruses, Flashkits immunostrips (ImmunoStrip Test Kit, USA) were used. Antiviral activity was calculated as a percentage of the number of plants without symptoms. The identification of phytopathogenic fungi was carried out by hybridization-fluorescence detection of PCR products in real time using the AriaDNA microchip nucleic acid amplifier (LUMEX LLC, Russia). The yield was determined by summing the mass of ripe fruits in each variant. The maximum insecticidal (85.3 %) and acaricidal (69.2 %) activity was recorded during suspension treatment of a 3-day culture of S. carpaticus RCAM04697. The highest antiviral activity (100 %) was also found when treated with S. carpaticus RCAM04697 suspension - all plants were without symptoms of cucumber mosaic virus and tomato mosaic virus. For bacterization with all strains of actinobacteria, the symptoms of diseases caused by Fusarium oxysporum and Alternari a infecta were completely absent. In the variant with the treatment of cucumber plants with a suspension of 3-day culture S. carpaticus RCAM04697 showed the highest biological efficiency at a high yield (62.9 kg), which was 3.8 times higher compared to the negative control. The studied strains can be recommended for further testing in industrial field experiments when growing vegetables in an integrated plant protection system.