Using the spermosphere model technique to describe the dominant nitrogen-fixing microflora associated with wetland rice in two Egyptian soils |
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| Authors: | A M N Omar C Richard P Weinhard J Balandreau |
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| Institution: | (1) Centre de Pédologie Biologique du C.N.R.S., B.P.5, F-54501 Vandoeuvre les Nancy, Cedex, France;(2) Institut Pasteur, Unité INSERM 199, 25 rue du Docteur Roux, F-75724 Paris, France |
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| Abstract: | Summary This study is an attempt to describe the dominant N2-fixing microflora associated with the roots of wetland rice. Rice cultivar Giza 171 was grown in a phytotron on two alluvial Egyptian soils for 8 days, a stage when the nitrogenase activity of undisturbed plants reached a level of 245 × 10–6 mol C2H4 h–1 g–1 dry weight of leaf. The roots and rhizosphere soils were then used for counting and isolating dominant diazotrophs. Counts and initial enrichment steps were carried out on a selective medium made of an axenic rice plantlet, the  spermosphere model , incubated under 1 % acetylene. The counts were very high, exceeding 108 bacteria g–1 dry weight of rhizosphere soil. Enterobacteriaceae were dominant; most isolates were Enterobacter cloacae belonging to different biotypes in the two soils. Enterobacter agglomerans, Citrobacter freundii and Klebsiella planticola were also present as members of the dominant microflora. Azospirillum brasilense and Azospirillum lipoferum were present as well, but less abundant. |
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| Keywords: | Rhizosphere N2-fixation Wetland rice Dominant microflora Spermosphere model Enterobacter cloacae Enterobacter agglomerans Citrobacter freundii Klebsiella planticola Azospirillum lipoferum Azospirillum brasilense |
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