Plant growth-promoting of olive and walnut actinobacteria: isolation, screening PGP traits, antifungal activities, identification, and hydroponic production of wheat

Bacteria are among the most frequently studied microorganisms in plant growth-promoting traits and fighting against different pathogens. Actinobacteria are prokaryotic organisms that produce mycelium, spores, and can form various secondary metabolites, especially antibiotics. In our study, free-living and endophytic Actinobacteria were isolated from rhizosphere soils and plant parts of olive (Olea europaea L.) and walnut (Juglans regia L.) trees, which are commercially essential agricultural products for Turkey. The study aimed to explore the plant growth-promoting activities of these Actinobacteria as biological fertilizers. Some of the properties of purified Actinobacteria that regulate the plant growth-promoting (PGP) traits; phosphate solubilization, indole-3-acetic acid, siderophore, ammonia, protease, beta-galactosidase, chitinase production, and antagonistic activities against various plant-pathogen fungi were investigated. As a result, 422 Actinobacteria were isolated, and 88 Actinobacteria determined to be possible plant bio-fertilizers were identified as Streptomyces spp. (70), Amycolatopsis spp. (12), Micromonospora spp. (four) and Nocardiopsis spp. (two) after the sequencing of their 16S rRNA genes. Moreover, four Streptomyces spp. and two Amycolatopsis spp. were used in hydroponic germination of wheat seeds (Triticum aestivum L.), and plant growth in terms of root and stem parts increased.