The aim of our work was to study the colonization of potato, tomato, rapeseed and camelina by associative microorganisms Methylobacterium mesophilicum, Pseudomonas aureofaciens BS1393 and Pseudomonas putida BS3701; examine the resistance of colonized plants to biotic (phytopathogens Erwinia carotovora and Sclerotinia sclerotiorum) and abiotic (naphthalene, oil) stressors. Colonized plants were characterized by an increased growth rate (1.5–2.0 times higher) compared to non-colonized ones; flower-bud formation, flowering and fructification of the colonized plants also started earlier. An increased resistance of colonized plants to phytopathogens, naphthalene (100 mµ/ml) and oil (0.7 %) was noted, too. The level of superoxide dismutase (SOD) in control plants on a medium with naphthalene or oil increased by 160–150%; in colonized plants – by 20–18 %. Colonized plants were more viable because of the presence of P. putida BS3701 on the roots.