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ARS Home » Midwest Area » St. Paul, Minnesota » Plant Science Research » Research » Publications at this Location » Publication #331156

Title: Persistence and diversity of rhizobial bacteria nodulating alfalfa

item Samac, Deborah - Debby
item CAO, YUANYUAN - Anhui Agricultural University
item Lenz, Peter
item FERGUSON, JOHN - University Of Minnesota
item NELSON, MATTHEW - University Of Minnesota
item Miller, Susan
item Dornbusch, Melinda - Mindy
item Klatt, Christian
item CASTLE, SARAH - University Of Minnesota
item SADOWSKY, MICHAEL - University Of Minnesota

Submitted to: Forage Focus
Publication Type: Trade Journal
Publication Acceptance Date: 7/15/2016
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Most alfalfa seed is treated with an inoculant consisting of several strains of the nitrogen fixing bacterium Sinorhizobium meliloti to enhance nodulation of seedlings. One strategy for increasing alfalfa forage yields, particularly in less fertile sites, is selection and use of highly competitive and efficient nitrogen fixing strains of rhizobia in the field. In other crops, inoculation of plant growth promoting bacteria (biologics) onto seeds has been shown to promote disease resistance and enhance growth. The objectives of this study are to characterize rhizobial strains nodulating alfalfa in two locations in Minnesota, identify bacteria associated with alfalfa nodules and determine their capacity for promoting plant growth. Analysis of the DNA fingerprints showed that bacteria from each location formed distinct populations (Fig.1). There were no differences in bacterial populations from 6-month-old and 18-month-old plants at either location but field isolates were significantly different from seed-derived strains. Populations at each site were highly diverse, with greater diversity at the Lamberton site. These results indicate that indigenous populations of S. meliloti remained high in the soil at each site in the absence of alfalfa and out-competed strains introduced on seeds on mature plants. A total of 380 bacterial strains were cultured from the outer nodule surface, which were identified to belong to seven classes of bacteria. About 50% could solubilize phosphate and 65% could produce the plant hormone indole acetic acid, which is involved in root and shoot growth. Interestingly, about 70% had activity against one pathogen and 18% had activity against two pathogens. None of the isolates appeared to inhibit growth of S. meliloti in lab assays. Isolates with multiple plant growth promoting activities will be tested for enhancing nodulation, plant biomass, and disease resistance. These results suggest that most of the bacteria associated with alfalfa root nodules are beneficial to plant growth.