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Title: GENETIC DIVERSITY OF BRADYRHIZOBIA NODULATING LUPINUS SPP.

Author
item BARRERA, L - INST. POLIT. NAC.,MEXICO
item TRUJILLO, M - INST. POLIT. NAC,MEXICO
item GOODFELLOW, M - MED. SCHOOL,NEW CASTLE,UK
item GARCIA, F - CIFN,UNAM,MEXICO
item DAVILA, G - CIFN, UNAM, MEXICO
item Van Berkum, Peter
item MARTINEZ-ROMERO, E. - CIFN, UNAM,MEXICO

Submitted to: International Journal of Systematic and Evolutionary Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/15/1997
Publication Date: N/A
Citation: N/A

Interpretive Summary: Rhizobia are important soil bacteria with application in agricultural production because they establish symbioses with legume crop plants. The symbiosis enhances the efficiency of growing crops under low input sustainable agricultural management practices because of biological nitrogen fixation. A problem in management of the symbiosis is that among the rhizobia there is considerable genetic variation in the capacity for nitrogen fixation and traits affecting plant-microbe interaction. Therefore, there is a need for genetic characterization of rhizobia permitting their positive identification. Symbionts of lupine are closely related to those of soybean and are native to soils in the Americas. Represenatives of a population of lupine symbionts was obtained from soils in Mexico, which unlike soils of the USA, do not harbor bacteria able to nodulate soybean. The isolates were diverse and were shownn to be close relatives of Bradyrhizobium japonicum, the symbiont of soybean. Estimates of chromosomal similarity between representatives of the isolates and B. japonicum indicated that they probably belong to different species. This information will be useful to microbiologists interested in plant-bacteria symbioses.

Technical Abstract: The genetic structure of Bradyrhizobium isolates recovered from three Lupinus species (L.campestris, L.monantus, and L. exaltatus) grown in Mexico was examined. Among 41 Bradyrhizobium isolates, 18 electrophoretic types (Ets) were distinguished by multilocus gel electrophoresis of five metabolic enzymes. The mean genetic diversity (H) of 0.64 indicated a large genetic diversity in the population sampled. Most isolates (63%) fell into two closely related clusters (I and II) and were the types most frequently isolated from the nodules of L.monantus and L. campestris. Isolates corresponding to ET cluster III were more frequent nodule occupants of L. exaltatus. The isolates also were assigned to three main groups using Curie point pyrolysis mass spectrometry. In general, good agreement was found between multilocus gel electrophoretic and pyrolysis mass spectrometric data. The 16S rRNA sequences of the representative Lupinus isolates were almost identical to those of two representatives of B. japonicum. However, the isolates were differentiated from B. japonicum strains in complimentary DNA::DNA relatedness studies.