Common beans (Phaseolus vulgaris L.) have centers of origin in both Mesoamerica and Andean South America, and have been domesticated in each region for perhaps 5000 years. A third major gene pool may exist in Ecuador and Northern Peru. The diversity of the rhizobia associated with beans has also been studied, but to date with an emphasis on the Mesoamerican center of origin. In this study we compared bean rhizobia from Mexico and Andean South America using both phenotypic and phylogenetic approaches. When differences between the rhizobia of these two regions were shown, we then examined the influence of bean cultivar on the most probable number (MPN) count and biodiversity of rhizobia recovered from different soils. Three clusters of bean rhizobia were distinguished using phenotypic analysis and principal-component analysis of Box AIR-PCR banding patterns. They corresponded principally to isolates from Mexico, and the northern and southern Andean regions, with isolates from southern Ecuador exhibiting significant genetic diversity. Rhizobia from Dalea spp., which are infective and effective on beans, may have contributed to the apparent diversity of rhizobia recovered from the Mesoamerican region, while the rhizobia of wild Phaseolus aborigineus from Argentina showed only limited similarity to the other bean rhizobia tested. Use of P. vulgaris cultivars from the Mesoamerican and Andean Phaseolus gene pools as trap hosts did not significantly affect MPN counts of bean rhizobia from the soils of each region, but did influence the diversity of the rhizobia recovered. Such differences in compatibility of host and Rhizobium could be a factor in the poor reputation for nodulation and N2 fixation in this crop.

Common beans (Phaseolus vulgaris L.) have centers of origin in both Mesoamerica and Andean South America, and have been domesticated in each region for perhaps 5000 years. A third major gene pool may exist in Ecuador and Northern Peru. The diversity of the rhizobia associated with beans has also been studied, but to date with an emphasis on the Mesoamerican center of origin. In this study we compared bean rhizobia from Mexico and Andean South America using both phenotypic and phylogenetic approaches. When differences between the rhizobia of these two regions were shown, we then examined the influence of bean cultivar on the most probable number (MPN) count and biodiversity of rhizobia recovered from different soils. Three clusters of bean rhizobia were distinguished using phenotypic analysis and principal-component analysis of Box AIR-PCR banding patterns. They corresponded principally to isolates from Mexico, and the northern and southern Andean regions, with isolates from southern Ecuador exhibiting significant genetic diversity. Rhizobia from Dalea spp., which are infective and effective on beans, may have contributed to the apparent diversity of rhizobia recovered from the Mesoamerican region, while the rhizobia of wild Phaseolus aborigineus from Argentina showed only limited similarity to the other bean rhizobia tested. Use of P. vulgaris cultivars from the Mesoamerican and Andean Phaseolus gene pools as trap hosts did not significantly affect MPN counts of bean rhizobia from the soils of each region, but did influence the diversity of the rhizobia recovered. Such differences in compatibility of host and Rhizobium could be a factor in the poor reputation for nodulation and N2 fixation in this crop.

Until recently, beans (Phaseolus vulgaris L.) grown in Minnesota were rarely inoculated. Because of this, we hypothesized that bean rhizobia collected in Minnesota would either share characteristics identifiable with Rhizobium etli of Mesoamerican or Andean origin, introduced into the region as seed-borne contaminants, or be indigenous rhizobia from prairie species, such as Dalea spp. The latter organisms have been shown to nodulate and fix N2 with Phaseolus vulgaris. Rhizobia recovered from the Staples, Verndale, and Park Rapids areas of Minnesota were grouped according to the results of BOXA1R-PCR fingerprint analysis into 5 groups, with only one of these having banding patterns similar to 2 of 4 R. etli reference strains. When representative isolates were subject to fatty acid - methyl ester analysis and 16S rRNA gene sequence analysis, the results obtained differed. 16S rRNA gene sequences of half the organisms tested were most similar to Rhizobium leguminosarum. Rhizobia from Dalea spp., an important legume in the prairie ecosystem, did not play a significant role as the microsymbiont of beans in this area. This appears to be due to the longer time needed for them to initiate infection in Phaseolus vulgaris. Strains of Rhizobium tropici IIB, including UMR1899, proved tolerant to streptomycin and captan, which are commonly applied as seed treatments for beans. Local rhizobia appeared to have very limited tolerance to these compounds.

No abstract

Uno de los mecanismos naturales que mejoran la eficiencia en la asimilación de nutrientes y aumenta el crecimiento de las plantas, es la asociación de éstas con micorrizas. En palmito se ha detectado la simbiosis, pero se desconocen los verdaderos efectos sobre el cultivo. En la presente investigación se determinó el efecto de diferentes concentraciones de micorrizas sobre el desarrollo y estado nutritivo de plántulas de palmito y se comprobó la acción de cuatro niveles de fósforo sobre la efectividad micorrízica, bajo dos alternativas de manejo del vivero. Se utilizó un DBCA en arreglo factorial 4X4+1, adicionalmente se realizó un análisis de variancia en Parcela Dividida para medir los cambios a través del tiempo de los tratamientos en las diferentes variables evaluadas, prueba de significación de Tukey al 5 % para tratamientos y niveles de los factores. La micorrización contribuyó a mejorar el crecimiento de las plantas de palmito, evidenciándose su efecto a partir de los 75 a 90 días después del trasplante, determinándose el efecto con más claridad en el índice de vigor de la planta, esto muestra que la simbiosis micorriza-planta tiene un tiempo de incubación variable dependiente del cultivo, ambiente, prácticas culturales y especie de micorriza. La dosis alta de micorriza M3 (60 g de micorriza comercial) y el nivel de 4,5 g de fósforo (P3) resultaron ser favorables para mejorar la respuesta en el desarrollo de las plantas. No se evidenció efectos negativos de las dosis de fósforo empleadas sobre la micorrización. El ADEVA condensado para las épocas de observación en las variables: altura de planta, diámetro del tallo, número de hojas e índice de vigor, confirmó los resultados antes indicados. No hubo diferencias estadísticas en el porcentaje de colonización, comparado con la cepa nativa. Los resultados del análisis foliar no mostraron efectos de la micorrización sobre el estado nutritivo del palmito. Estadísticamente la micorriza comercial mejoró a nivel foliar la concentración de Mn.