Seasonal Variation of Rhizobium meliloti in Alfalfa Hay and Cultivated Fields in North Carolina1
- R. L. Mahler and
- A. G. Wollum2
Little is known about native populations of rhizobia in soils of the southeastern United States. This study was undertaken to observe the influence of season on fluctuations of native soil Rhizobium meliloti populations in cultivated and alfalfa (Medicago saliva L.) hay field environments throughout North Carolina.
Soil samples were collected from the Ap horizons of fields in three physiographic regions of North Carolina every 30 days for a 14-month period. Rhizobium meliloti were enumerated using a most-probable-number (MPN) technique and alfalfa as the host for plant infectivity tests. Serial dilution and pour plate techniques were used to determine bacteria.
The cultivated fields did not have a recent history of alfalfa. Conversely, alfalfa hay fields had been in alfalfa continuously for at least 2 years. Larger soil populations of R. meliloti existed in alfalfa hay fields than in cultivated fields. Seasonal variation was evident in North Carolina alfalfa hay fields with populations averaging 1.3 ✕ 105/g soil in April and 1.2 ✕ 104/g in October. Seasonal distribution differences were not noted in cultivated fields. Rhizobium meliloti constituted from 0.01 to 1.67% of the total aerobic bacterial population in alfalfa fields and < 0.001 to 0.01% of the population in cultivated fields.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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