(15)N-determined dinitrogen fixation potential of genetically diverse bean lines (Phaseolus vulgaris L.)

El mejoramiento de la fijacion de N2 en frijol depende de la seleccion de genotipos vegetales superiores y de la presencia de cepas eficientes de rhizobio. Se realizo un estudio para evaluar lineas de frijol con diversidad genetica por potencial de fijacion de N2, utilizando la tecnica de dilucion de (15)N reducido, en condiciones de campo en Wisconsin, EE.UU. Plantas de 21 lineas de frijol y 3 isolineas de soya, no noduladoras, recibieron aplicaciones de sulfato de amonio de (15)N reducido. Los brotes cosechados en los estadios V6, R3 y R7 y las semillas secas se analizaron por N total mediante el procedimiento Kjeldahl y se determino la razon de (15)N a (14)N en un espectrometro de masas MAT 250. Se determino la poblacion de nodulos de la cepa de R. leguminosarum bv. phaseoli CIAT 899 aplicada, en 5 de las lineas de frijol. El contenido total de N de los brotes mostro un patron de acumulacion similar al PS y al N2 fijado en los brotes. Con base en contenido total de N, N2 fijado y PS de los brotes, Riz 30 y Preto Cariri se identificaron como buenos fijadores ya que Puebla 152 y Cargamanto al parecer inician la fijacion de N2 en una etapa temprana. Ademas, algunas lineas de frijol que fijaron una cantidad considerable de N2 no distribuyeron gran parte de el a los granos. Preto Cariri acumulo 21.2 kg de N/ha en las semillas en comparacion con Puebla 152 que acumulo 43.8 kg de N/ha del N2 fijado en los granos. En el muestreo inicial, Puebla 152 y 22-27 mostraron un porcentaje mucho mayor de nodulos de la corona formados por la cepa inoculante CIAT 899 que Rio Tibagi, que se considera un fijador deficiente de N2. (RA-CIAT) spa

Improvement of dinitrogen fixation in beans (Phaseolus vulgaris L.) will depend on the selection of superior plant genotypes and the presence of efficient rhizobial strains. This study was conducted to evaluate diverse bean lines for N2 fixation potential using the (15)N-depleted dilution technique under field conditions in Wisconsin, USA. Plants of 21 bean lines and three non-nodulating isolines of soybean received applications of (15)N-depleted ammonium sulphate. Shoots harvested at the V6, R3 and R7 stages and dry seeds were analyzed for total N using the Kjeldahl procedure, and the ratio of (15)N to (14)N was determined on a MAT 250 mass spectrometer. Nodule occupancy of the applied strain of R. leguminosarum biovar phaseoli, CIAT 899, was determined in five of the bean lines. Total shoot N content showed a pattern of accumulation similar to shoot dry weight and fixed N2 in the shoot. Based on shoot total N, N2 fixed in the shoot and shoot dry weight Riz 30 and Preto Cariri were identified as being as good fixers as Puebla 152 and Cargamanto appear to begin N2 fixation early. Furthermore, some bean lines that fixed considerable N2 did not translocate a large amount of N to the grains. Preto Cariri accumulated 21.2 kg N ha(-1) in the seeds compared to Puebla 152 which accumulated 43.8 kg N ha(-1) of the fixed N2 into the grains. At the early sampling, Puebla 152 and 22-27 had a considerable higher percentage of their crown nodules formed by the inoculant strain CIAT 899, than did Rio Tibagi which has been considered a poor N2 fixer. (AS) eng