Azospirillum inoculation in pregerminating wheat seeds

Azospirillum cells were inoculated in pregerminating wheat during seed imbibition. Surface-sterilized seeds of Triticum aestivum cv. Buck Pucara were sequentially soaked for 3 h in water and 3 h in the inoculum of 3 x 10(8) Azospirillum brasilense Sp 245 cells . mL(-1), to allow bacteria to enter during imbibition. Germination and seedling growth were accomplished in sterile distilled water at 20 degrees C, in the dark. To compare with more traditional methods based on plant-Azospirillum colonization after germination, seedlings from noninoculated seeds were inoculated in parallel by immersing roots in the same inoculum, for the same period of time. Autoclaved inocula were used as controls in all cases. We observed about 5 x 10(8) Azospirillum cells . g(-1) fresh weight in 11-day-old wheat seedlings inoculated before or after seed germination. However, roots from seed-inoculated seedlings had higher both bacterial concentration and length. On the other hand, seeds inoculated during imbibition and dried to 14% water content retained 3.7 x 10(6) viable cells . g(-1) dry weight up to 27 days. Moreover, seeds stored for 30 days were not only able to germinate but also to harbor over 10(6) cells g(-1) fresh weight in roots after 7 days growth. Here we present the possibility of obtaining in a simple and inexpensive way, seeds containing high numbers of viable Azospirillum cells, which could avoid the use of external carriers or adhesives.