Occurrence of diazotrophic bacteria and arbuscular mycorrhizal fungi on the cassava crop

This study was performed to evaluate the occurrence and to isolate and iden tify diazotrophic bacteria and arbuscular mycorrhizal fungi associated with the cassava(Manihot esculenta) crop. Samples from rhizospherical soil, roo ts, tubers, stems and leaves from several localities of the States of Rio d e Janeiro, Sao Paulo and Parana in Brazil, were inoculated in three media s pecific for diazotrophic associative bacteria, LG1-P, NFb-malate and NFb-GO C, evaluating the most probable number of cells and the acetylene-reducing activity. Diazotrophic bacteria were detected in all plant parts except for the leaves, and were identified as Klebsiella sp., Azospirillum lipoferum and a bacterium called "E", probably belonging to the Burkholderia genus. B acterium E was able to accumulate, in the N-free semi-solid media, from 7.6 3 to 14.84 mg of N/g of C and to maintain N fixation capacity after ten con secutive transferences. Mycorrhizal root colonization varied from 31% to 69 % and spore density from 10 to 384 spores/100 mt of soil, predominating the species Entrophospora colombiana and Acaulospora scrobiculata in Rio de Ja neiro, A. scrobiculata and Scutellospora helerogama in Parana and in Piraci caba (Sao Paulo), and A. appendicula and S. pellucida in Campinas (Sao Paul o).