Isolation and characterization of diazotrophic bacteria from banana and pineapple plants

Banana and pineapple fruit crops are widely cultivated in tropical areas wh ere high amounts of fertilizers are applied, principally nitrogen. Over 200 kg N.ha(-1).yr(-1) is often applied to these crops. Nevertheless, developi ng countries face the problem of high costs of chemical fertilizers. As alr eady demonstrated for other tropical crops, like sugar cane, the utilizatio n of nitrogen-fixing bacteria may support the growth of these fruit plants. In this work, we demonstrate the association of nitrogen-fixing bacteria w ith banana and pineapple. Samples from roots, stems, leaves and fruits of d ifferent genotypes showed the occurrence of diazotrophic bacteria, when eva luated in semi-specific semi-solid media. These isolates could be separated into seven different groups according to their morphological and physiolog ical characteristics. Additional, phylogenetic assignments were performed w ith group- and species-specific oligonucleotide probes. Bacteria related to the groups of Azospirillum amazonense, Azospirillum lipoferum, Burkholderi a sp. and a group similar to the genus Herbaspirillum could be detected in samples of both crops. However, Azospirillum brasilense and another two gro ups of Herbaspirillum-like bacteria were detected only in banana plants. Tw o isolates of the latter group were identified as Herbaspirillum seropedica e, whereas the other isolates may represent a new Herbaspirillum species.