The endophyte Enterobacter sp. FD17: a maize growth enhancer selected based on rigorous testing of plant beneficial traits and colonization characteristics

With the aim to select powerful microbial strains to be used for the enhancement of maize yield and resistance to abiotic and biotic stresses, we tested five endophytic bacterial strains previously isolated from maize roots. A range of different laboratory assays in regard to potential plant growth promotion was performed and strains were further evaluated for improving growth of five maize cultivars under axenic and natural soil conditions. Endophytic colonization was an additional component in our selection process as it is of high importance for an inoculant strain to efficiently colonize the plant environment. All strains had the potential to improve maize seedling growth under axenic conditions. Enterobacter sp. strain FD17 showed both the highest growth-promoting activity under axenic conditions as well as colonization capacity. FD17 was therefore selected for further plant tests in a net house, in which two different maize cultivars were grown in large pots until ripening and subjected to outdoor climatic conditions. Results showed that inoculation significantly increased plant biomass, number of leaves plant^?1, leaf area, and grain yield up to 39 %, 14 %, 20 %, and 42 %, respectively, as compared to the un-inoculated control. Similarly, inoculation also improved the photochemical efficiency of photosystem II (PSII) of maize plant and reduced the time needed for flowering. We also confirmed that strain FD17 is able to colonize the rhizosphere, roots and stems. Based on rigorous testing, Enterobacter sp. strain FD17 showed the highest potential to promote growth and health of maize grown under natural conditions. This study suggested that in vitro plant growth-promoting traits and potential of maize seedling growth promotion by bacterial endophytes could be used for the selection of potential inoculant strains subjected for further testing as bio-inoculant under field conditions.