Studiesin the early 20th century revealed that plants and diazotrophic bacteria can establish associations enabling nitrogen fixation [24]. These findings have sparked an increased interest for identifying bacteria able to improve nitrogen nutrition in agricultural settlements. A considerable number of diazotrophs have been identified so far to associate as epiphytes or endophytes, primarily with cereals and grasses (Figure 1c), but only in few instances the actual plant nutrition with bacterial fixed nitrogen was demonstrated