Levels and identities of nonrhizobial microorganisms found in commercial legume inoculant made with nonsterile peat carrier

Abstract

Sixty samples of commercial North American legume inoculants manufactured for sale in 1994 using nonsterile peat as carrier were tested for Rhizobium (or Bradyrhizobium) content and non-Rhizobium biological contaminant load. Products of three major producers of such inoculants for sale in Canada were examined. Viable Rhizobium content varied from 5.6 x 10(5) to 8.1 x 10(9) cells/g, while the contaminant load varied from 1.8 x 10(8) to 5.5 x 10(10) cfu/g. Most of the inoculants contained more nonrhizobial organisms than they did rhizobia. Identifications were made of the most numerous nonrhizobial bacteria occurring in 100 samples of inoculants collected in 1993 and 1994. The most commonly identified contaminant was Xanthomonas maltophilia. Pseudomonas aeruginosa, Klebsiella pneumoniae, and Enterobacter cloacae were also found at high levels in some products. Contaminant organisms capable of inhibiting rhizobial growth in plate culture were found in the products of all three manufacturers.

New Approaches for Bioaugmentation as a Remediation Technology

“…243 Numerous different carrier materials have been used including biosolids, charcoal-amended soil, clay, lignite, manure, and peat. 11,13,104,113,164,243 Most of the research on the different carrier materials has been for agricultural legume inoculants, with peat being the most commonly used. 164,243,244 Research has indicated that presterilization of the carrier can increase the inoculant's shelf life.…”

“…11,13,104,113,164,243 Most of the research on the different carrier materials has been for agricultural legume inoculants, with peat being the most commonly used. 164,243,244 Research has indicated that presterilization of the carrier can increase the inoculant's shelf life. 228 The results of Van Dyke and Prosser 242 also demonstrate that preincubation of the inoculant in a sterile carrier can enhance its ultimate survival in environment.…”

Field comparison of pre-inoculated alfalfa seed and traditional seed inoculation with inoculant prepared in sterile or non-sterile peat

“…This is surprising considering that some of the contaminants that have been detected in non-sterile peat inoculant products are antagonistic to rhizobia (3). This is surprising considering that some of the contaminants that have been detected in non-sterile peat inoculant products are antagonistic to rhizobia (3).…”

“…Commercial products include both sterile and non-sterile formulation, but in North America, most inoculant products are prepared with non-sterile peat (2,3). Olsen et al (3,4) examined North American inoculants using non-sterile peat and found a high frequency of non-rhizobial contaminants. However, it is unclear whether the relative effectiveness of inoculants manufactured using non-sterile peat is different from those made using sterile peat.…”

A very rapid enzyme immunoassay for confirmation of rhizobial identity and estimation of cell numbers in fresh broth culture

“…Unfortunately, much of the rhizobial inoculant produced in the world today is of poor quality (Somasegaran 1991;Brockwell and Bottomley 1995). Recent documentation exists of legume inoculant sold, in both developed and developing countries, that contained no detectable rhizobia (Thompson 1991;Olsen et al 1996a).…”