In vitro and in vivo inoculation of four endophytic bacteria on Lycopersicon esculentum

Four bacteria selected on the basis of their capability of fixing atmospheric nitrogen, stimulating plant-growth, and protecting the host plant from pathogens - Azospirillum brasilense, Gluconacetobacter diazotrophicus, Herbaspirillum seropedicae, Burkholderia ambifaria – were inoculated on tomato seeds either singularly, in couple and in a four bacteria mixer. Aim of this research was to evaluate: 1) effect of single and mixed cultures on the inoculated plant - plant growth, dry weight, root length and surface, number of leaves, etc. 2) colonization and interactions of the bacteria inside the host plant; 3) localization inside the host of single bacterial strains marked with the gusA reporter gene. The results obtained indicate that all selected microbial strains have colonized Lycopersicon esculentum but in a different way, depending on the single species. Azospirillum brasilense, Gluconacetobacter diazotrophicus inoculated in vitro singularly and together were the best plant colonizers. in vivo essays, instead, Burkholderia ambifaria and the four-bacterium mixer gave the best results. It was possible to localize both Azospirillum brasilense and Herbaspirillum seropedicae inside the plant by the gusA reporter gene. The bacterial strains occur along the root axis from the apical zone until to the basal stem, on the shoot from the base up to the leaves. The four bacteria actively colonize tomato seeds and establish an endophytic community inside the plant. This review gives new information about colonization processes, in particular how bacteria interact with plants and whether they are likely to establish themselves in the plant environment after field application as biofertilisers or biocontrol agents.