How rice seed bacteria colonize the grain is not yet understood. One possibility is by lateral transmission through water, wind, or biological vector dispersion, which facilitates microorganism movement to inflorescences (Robertson and Alexander, 1994; Mundt et al., 1999). Otherwise, bacteria may migrate from the colonized root system to aerial tissues and inflorescences during grain filling (Chi et al., 2005). Thus, seed loading with PPB would ensure their presence from the very early stages of seedling development to improve germination success and establishment in the soil (Rosenblueth and Martinez-Romero, 2006).