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Effect of inoculation of Azospirillum spp. on nitrogen accumulation by field-grown wheat

ROBERT M. BODDEY, VERA L. D. BALDANI, JOSÉ I. BALDANI and JOHANNA DÖBEREINER
Plant and Soil
Vol. 95, No. 1 (1986), pp. 109-121
Published by: Springer
Stable URL: http://www.jstor.org/stable/42935776
Page Count: 13
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Effect of inoculation of Azospirillum spp. on nitrogen accumulation by field-grown wheat
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Abstract

Two experiments were performed to examine the effects of inoculation of field grown wheat with various Azospirillum strains. In the first experiment the soil was sterilized with methyl bromide to reduce the Azospirillum population and ¹⁵N labelled fertilizer was added to all treatments. Two strains of Azospirillum brasilense isolated from surface sterilized wheat roots and the A. brasilense type strain Sp7 all produced similar increases in grain yield and N content. From the ¹⁵N and acetylene reduction data it was apparent that these increases were not due to N₂ fixation. In the second experiment performed in the same (unsterilized) soil, two A. brasilense strains (Sp245, Sp246) and one A. amazonense strain (Am YTr), all isolated from wheat roots, produced responses of dry matter and N content while the response to the strain Sp7 was much smaller. These data confirm earlier results which indicate that if natural Azospirillum populations in the soil are high (the normal situation under Brazilian conditions), strains which are isolated from wheat roots are better able to produce inoculation responses than strains isolated from other sources. The inoculation of a nitrate reducíase negative mutant of the strain Sp245 produced only a very small inoculation response in wheat. This suggests that the much greater inoculation response of the original strain was not due to N₂ fixation but to an increased nitrate assimilation due to the nitrate reductase activity of the bacteria in the roots.

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