ACETOBACTER-DIAZOTROPHICUS, AN INDOLEACETIC-ACID PRODUCING BACTERIUM ISOLATED FROM SUGARCANE CULTIVARS OF MEXICO

Thirteen cane cultivars grown on fields in Mexico were sampled to assess the occurrence of Acetobacter diazotrophicus, a recently identified N2-fixing bacterium. Results showed that the isolation frequencies extended over a broad range (1.1 to 67%), likely to be related to the nitrogen fertilization level. The lowest isolation frequencies (1.1 to 2.5%) were obtained from plants growing at high nitrogen doses (275-300 kg ha-1) and the highest values (10-67%) from plants cultivated with 120 kg N ha-1. All eighteen strains of A. diazotrophicus produced indoleacetic acid (IAA) in defined culture medium. Estimates obtained from HPLC analyses revealed that A. diazotrophicus strains produced from 0.14 to 2.42 mug IAA mL-1 in culture medium. Considering that A. diazotrophicus is found within the plant tissue, the biosynthesis of IAA suggests that the bacteria could promote rooting and improve sugarcane growth by direct effects on metabolic processes, in addition to their role in N2 fixation.