Quantitative comparison of the laboratory and field competitiveness of Rhizobium leguminosarum biovar phaseoli

Abstract

Rhizobium leguminosarum bv. phaseoli KIM5s outcompeted strain CE3 in bean (Phaseolus vulgaris L.) root nodulation when plants were grown at any of three field sites, each with a different soil type and indigenous population, or in the laboratory in a sterilized sand, a sterilized peat-vermiculite mixture, or a nonsterile field soil. A mathematical model describing nodulation competitiveness was empirically derived to evaluate the relative competitiveness of the two strains under these conditions. This model relates the proportional representation of the two strains in the inoculum to the proportional representation of nodules occupied by each strain or both strains and provides a measure of competitiveness, which is referred to as the competitiveness index. Statistical comparisons of competitiveness indices showed that the relative competitiveness of KIM5s and CE3 remained constant when the two strains were applied in a constant ratio over a range of inoculum concentrations, from 103 to 107 cells per seed, and when they were applied in various ratios to six P. vulgaris cultivars. Furthermore, the relative competitiveness of KIM5s and CE3 in the laboratory did not differ significantly from their relative competitiveness at the three field sites studied. Thus, a study of the basis for nodulation competitiveness of KIM5s and CE3 in the laboratory has the potential to provide an understanding of competitiveness both in the laboratory and in the field.

Foliar Chlorosis in Symbiotic Host and Nonhost Plants Induced by Rhizobium tropici Type B Strains

“…Plant growth conditions. Bean seeds were surface disinfected and planted in large test tubes containing sterile sand and vermiculite as described previously (1,2). Unless otherwise noted, the bean cultivar WBR22-34 was used in all experiments (4).…”

Serological and Ecological Characteristics of a Nodule-Dominant Serotype from an Indigenous Soil Population of Rhizobium leguminosarum bv. trifolii

“…Legumes can nodulate preferentially with one of two rhizobial strains even when the preferred strain is outnumbered by the other strain (6,16,49,53). Many laboratory studies have shown, however, that plant preference for a particular strain can be overridden by changing the population ratio of the two competing strains (2,3,15,20,21,23,25,34,37,44). Although there may be differences between the population densities of different strains in soils under field conditions and these differences may influence the outcome of nodulation on fieldgrown plants, these possibilities have received little attention.…”

Symbiotic Characteristics of Rhizobium leguminosarum bv. trifolii Isolates Which Represent Major and Minor Nodule-Occupying Chromosomal Types of Field-Grown Subclover ( Trifolium subterraneum L.)

“…Support for this hypothesis comes from situations where specific strains or subpopulations dominate nodules regardless of their relative contributions to an inoculant mixture or to a soil population (37,42). In contrast, several studies have shown that nodulation success by specific strains is influenced by the relative numbers of these strains in a mixture of strains (2,4,(20)(21)(22)33). In these cases, relative nodule occupancy can be changed if the ratio of strains is changed (2,14,21,22).…”