Composition and properties of the actinomycete flora in a ferralitic tropical soil (oxisol)-sugar cane ecological system.

Streptomycetes constituted about 46--48 per cent of the total aerobic microflora in the cultivated horizon of the studied ferralitic tropical soil below sugar cane plantation. This streptomycete fraction of the soil microbial community was composed of 13 (or more) species of Streptomyces (S. chromofuscus, S. chromogenus, S. diastatochromogenes, S. flavochromogenes, S. griseolus, S. nigrescens, S. phaeofaciens, S. sterilis, S. violaceus, Streptomyces sp. I--III), and Streptoverticillium (Sv. aspergilloides). None of these organisms did occur, with detectable frequency of occurrence, in the root surface region of sugar cane. Here, in the rhizoplane, we found a numerically small population of streptomycetes (about 5 per cent of the total bacterial flora), composed of two species (Streptomyces sp. IV and S. griseorubiginosus) which were, however, not detected in soil samples.