Genetic diversity and inoculation of plant-growth promoting diazotrophic bacteria for production of Eucalyptus urophylla seedlings

Abstract

The study of diversity and the established relationship between plants and endophytic bacteria contribute significantly to the plant development. This study aimed to isolate, identify plant-growth promoting diazotrophic bacteria from Eucalyptus urophylla plants and evaluate the plant seedling response to inoculation with selected strains. The study was conducted from July 2017 to August 2018 set up in a greenhouse in a completely randomized experimental design with 17 treatments and 16 replicates, with 12 strains isolated from E. urophylla, four standard bacteria and one control (not inoculated with bacteria). Twelve strains were isolated from the eucalyptus rhizosphere using the N-free semisolid media and the 16 rRNA sequencing identified species closely related to Nitrospirillum amazonense, Stenotrophomonas maltophilia, Pantoea agglomerans, Herbaspirillum frisingense and Ideonella dechloratans. All strains were able to produce indol compounds and the presence of the nifH gene (nitrogen fixation) was demonstrated by PCR analysis. There was a significant effect of the strain inoculation on the height, diameter, root dry matter, root length, root area surface and volume of the seedling plant. The strains L1E, L4E - Azospirillum amazonense and L7E - Stenotrophomonas maltophilia presented high values variables of height, diameter, root dry matter, root length, root area surface and volume. Many of the bacterial strains were able to promote plant growth either by root morphology changes or biomass accumulation in root and shoots. Therefore, there is a biotechnological potential of these plant-growth promoting diazotrophic bacteria strains to be applied as inoculants to improve growth of eucalyptus seedlings. This fact opens new opportunities to establish forests with economically viable and environmentally sustainable technologies