Fig. 2

Basic and applied aspects related to the biological input designed with combined use of diazotrophic endophytic bacteria (DEB) and humic acid (HA). A–C Showing positives effect of the technology on root branching, root biomass and shoot biomass from lab to field experiments. D, E Light microscopy (LM) of maize root segments (R) comparing treated plants (DEB + HA) against mock plants. Note clear increase in density and length of root hairs (arrows). F LM from maize root tip (RT) showing border cells (BC) released trigged by HA. G Scanning electron microscopy (SEM) from the maize root tip (RT) showing root cap eroded by released border cells (BC). H LM from released border cells (BC) encapsulated by self-organized humic particles in suspension (HA). I SEM from maize root (R) surface colonized by Herbaspirillum seropedicae strain HRC54 aggregates in association with humic acid particles. J SEM from maize root surface close to the region of a lateral root emerged. Note crack developed in the epidermal layer (arrow head) and H. seropedicae strain HRC54 attached to the surface close to the entrance point (white arrows). K Epifluorescent microscopy (EM) of H. seropedicae strain RAM 10 linked with a green fluorescent protein marker (arrow) forming a cluster around to a humic acid particle. L EM of a maize root segment colonized by a very active H. seropedicae strain RAM 10 biofilm (arrows). M SEM of humic acid (HA) plates associated with H. seropedicae strain HRC54 attached to the sugarcane leaf surface after foliar spray. Bar equal 100, 100, 200, 200, 50, 5, 5, 10, 150 and 20 µM, respectively, for D–M