Azospirillum inoculation of maize seed during imbibition

Maize seeds (Zea mays, L.) hybrid DK 636 (FAO 530) were inoculated either with live (L) or control (autoclaved) Azospirillum brasilense BR 11005 cells during imbibition. Seeds were then dried up to 14% humidity, and stored at 15 - 20 degrees C in the dark. After 0, 5, 15, and 25 days of storage, seeds were germinated in the dark in a humid chamber at 20 degrees C, and seedlings were grown for 5 days. Afterwards, length, fresh weight (FW), dry weight (DW), and water content (WC) were determined in coleoptiles, while roots were used to determine Azospirillum most probable number (MPN), DW and root surface. The growth-promoting effect of Azospirillum on root DW and radical surface was significantly evident in all periods of seed storage. However, the effects on coleoptile length, DW and WC were significant only after 15 days of storage. On the other hand, Azospirillum MPN in roots of seedlings from L seeds was 10(8) cells g(-1) at 0 and after 5 days of seed storage, while decreasing to 10(7) and 10(5) at 15 and 25 days, respectively. These results indicate an optimal bacterial concentration of 10(8) - 10(7) cells g(-1) of roots, for a general growth promotion effect on maize seedlings, and 10(5) to have an effect in roots only. The inoculation system adopted here was able to maintain this last MPN even after drying and storing seeds for up to 25 days.