Occurrence of diazotrophic bacteria in different sugar cane genotypes

The objective of this work was to find out the localization and number of e ndophytic bacteria in four sugar cane genotypes and investigate upon the po ssible existence of correlation to the results obtained in some studies abo ut quantification of biological nitrogen fixation (BNF). A survey of the di azotrophic bacteria present in sugar cane genotypes differing in their capa city to obtain nitrogen through BNF was performed, and population of Herbas pirillum spp. and Acetobacter diazotrophicus was quantified. The bacteria t ested in the survey were Azospirillum lipoferum, A. brasilense, A. amazonen se, Herbaspirillum spp. and Acetobacter diazotrophicus. All these bacteria were present in the four genotypes and were found in all parts of the plant s, except A. amazonense which was not isolated from leaf samples. The quant ification of Herbaspirillum spp. and A. diazotrophicus showed that there we re no significant differences among the sugar cane genotypes and, generally , the bacteria were in greater number in roots. While number of Herbaspiril lum spp. remained stable during the lifecycle of the culture, the populatio n of A. diazotrophicus suffer a decrease with the approach of the end of th e commercial cycle. It is suggested that the differences in the rates of BN F found in sugar cane genotypes are not caused by differences in the presen ce or the number of the bacterial species studied hem.