Isolation and characterization ofAzotobacterandAzospirillumstrains from the sugarcane rhizosphere.

Bacteria with the ability to grow on nitrogen-free media and with nitrogenase activity under aerobic or microaerobic conditions were isolated from sugarcane roots collected from four different agricultural locations in Granada (Spain). Isolates were Gram negative rods and were identified asAzotobacter chroococcumandAzospirillum brasilense. Our results suggest thatAzotobacterisolates do not have a particular affinity for sugarcane rhizospheres and that, on the contrary,Azospirillumisolates show specific association and perhaps endophytic colonization of sugarcane. However, obligate endophytes (Gluconacetobacter diazotrophicus) were not found in the apoplastic fluid of the stems and macerates extracts of sugarcane tissues with the procedure applied. Population of this microorganism might be in low number in the Spanish sugarcane varieties studied which is also discussed. [ABSTRACT FROM AUTHOR]