Many seeds carry endophytes, which ensure good chances of seedling colonization. In this work, we have
studied the seed-borne bacterial flora of rice varieties cultivated in the northeast of Argentina. Surface-steri-
lized husked seeds of the rice cultivars CT6919, El Paso 144, CAMBA, and IRGA 417 contained an average
of 5×106
CFU/g of mesophilic and copiotrophic bacteria. Microbiological, physiological, and molecular char-
acterization of a set of 39 fast-growing isolates from the CT6919 seeds revealed an important diversity
of seed-borne mesophiles and potential plant probiotic activities, including diazotrophy and antagonism of
fungal pathogens. In fact, the seed-borne bacterial flora protected the rice seedlings against Curvularia sp.
infection. The root colonization pattern of 2 Pantoea isolates from the seeds was studied by fluorescence
microscopy of the inoculated axenic rice seedlings. Both isolates strongly colonized the site of emergence
of the lateral roots and lenticels, which may represent the entry sites for endophytic spreading. These findings
suggest that rice plants allow grain colonization by bacterial species that may act as natural biofertilizers
and bioprotectives early from seed germination.
Keywords: rice, seed, plant probiotic bacteria, diversity, root colonization, Pantoea