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Nineteen rhizobium strains were isolated from the nodules of the legumes Canavalia ensiformis, Stylosanthes guianensis, Centrosema molle, Pueraria phaseoloides and Macroptilium atropurpureum, with the objective of obtaining effective inoculants for such crops in acid soils. For the characterization of the bacterial isolates, their micromorphological, staining and cultural characteristics were studied, as well as some physiological-biochemical responses, such as the excretion of acid or base to the culture medium and the cetolactase assay. An in vitro nodulation essay was performed with each legume to determine the effectiveness of the isolates. According to the cultural characteristics, the growth rate in YMA method and the production of acid or base, the isolates obtained could belong to the genera Bradyrhizobium and Rhizobium and/or Sinorhizobium. The cetolactase test allowed to learn that none of the studied isolates belongs to the Agrobacterium genus. The trial with inoculated plants showed that all the isolated strains were effective in nodulation, because they nodulated in the tested legumes. It is concluded that from the isolated strains, 11 could belong to the genus Bradyrhizobium, while the other eight share similar characteristics with the genera Rhizobium and/or Sinorhizobium; all the isolates were effective in nodulation and they can be considered promising strains for obtaining inoculants for the studied forage legumes. [ABSTRACT FROM AUTHOR]

Lipo-chitooligosaccharides produced by rhizobia are a class of signalling molecules mediating nodule recognition and organogenesis in the Rhizobium--leguminous symbiosis. Their synthesis is determined by rhizobiumnodulating genes; therefore, they are commonly known as Nod factors. This review is a compilation of updated information on some general topics, as Rhizobium-leguminous interaction signals, nod factor structure, as well as their role in symbiosis. Besides, a research view about this subject in Cuba is presented, describing results related to the design and optimization of culture media with nod factor inducers, with quorum sensing, with nod factor anti-stress effect, with the use of nod factor synthesis-induced inoculants and other oligosaccharines, and with the possible beneficial effect of the latter ones on bacterium-leguminous symbiosis. [ABSTRACT FROM AUTHOR]