Promising applications of growth-promoting bacteria for improving the development of apple seedlings

The article presents a study of the eff ects of growth-promoting bacteria on the growth, viability, and physiological condition of apple seedlings. The experiment was conducted in 2024–2025 in the area adjacent to the Pervomaysky Culture and Recreation Park (Ufa, Republic of Bashkortostan, Russia). The study used two-year-old seedlings of the Terentyevka apple cultivar (Malus terentyevka, Malus plodovitka) grown in a forest nursery (Ufa district, Republic of Bashkortostan). For plant treatment, two strains of gram-negative growth-promoting bacteria from the Сulture Сollection of the Ufa Institute of Biology, Ufa Federal Research Center of the Russian Academy of Sciences, were used: Pseudomonas protegens DA1.2 (No. B-3542D in the All-Russian Collection of Microorganisms) and P. chlororaphis 4CH (No. UIB-57 in the Culture Collection of the Ufa Institute of Biology). Both strains possess nitrogen-fi xing activity and the ability to synthesize auxins. Treatment was performed by applying bacterial suspensions twice to the soil in the root zone in 2024. During the experiment, biometric parameters (changes in stem length), as well as the content of pigments (chlorophyll, fl avonoids, and anthocyanins) and oxidative stress markers (malondialdehyde [MDA] and proline) in leaves were assessed. The results demonstrated a stimulatory eff ect of both bacterial strains, expressed as accelerated shoot growth. The growth of apple seedlings treated with P. protegens DA1.2 and P. chlororaphis 4CH was 69 and 40 % greater, respectively, than that of the control plants. Treatment with both strains increased leaf chlorophyll content and nitrogen balance index by up to 28 and 33 %, respectively, relative to untreated plants. Moreover, an antistress eff ect of the bacterial strains was observed during adaptation to external environmental conditions, as indicated by decreases in proline (by 3545 %) and MDA (15–32 %) levels in treated plants. The results demonstrate the potential for developing microbiological fertilizers based on the studied growthpromoting Pseudomonas strains for use in apple seedling production.

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