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Comparison of Benefit to Sugarcane Plant Growth and 15N2 Incorporation Following Inoculation of Sterile Plants with Acetobacter diazotrophicus Wild-Type and Nif¯ Mutant Strains

March 2001 , Volume 14 , Number  3
Pages  358 - 366

Myrna Sevilla , 1 Robert H. Burris , 2 Nirmala Gunapala , 1 and Christina Kennedy 1

1Department of Plant Pathology, University of Arizona, P.O. Box 210036, Forbes 204, Tucson 85721, U.S.A.; 2Department of Biochemistry, University of Wisconsin, Madison, U.S.A.

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Accepted 28 November 2000.

The ability of the nitrogen-fixing bacterial endophyte Acetobacter diazotrophicus strain PAl5 to enhance the growth of sugarcane SP70-1143 was evaluated in the growth chamber, greenhouse, and field by comparing plants inoculated with wild-type and Nif¯ mutant MAd3A in two independent experiments. The wild-type and Nif¯ mutant strains colonized sugarcane plants equally and persisted in mature plants. In N-deficient conditions, sugarcane plants inoculated with A. diazotrophicus PAl5 generally grew better and had a higher total N content 60 days after planting than did plants inoculated with mutant MAd3A or uninoculated plants. These results indicate that the transfer of fixed N from A. diazotrophicus to sugarcane might be a significant mechanism for plant growth promotion in this association. When N was not limiting, growth enhancement was observed in plants inoculated with either wild-type or Nif¯ mutants, suggesting the additional effect of a plant growth promoting factor provided by A. diazotrophicus. A 15N2 incorporation experiment demonstrated that A. diazotrophicus wild-type strains actively fixed N2 inside sugarcane plants, whereas the Nif¯ mutants did not.

Additional keywords: Acetobacteraceae, biological nitrogen fixation, diazotrophs, endophytes, grasses, meristem tissue culture.

© 2001 The American Phytopathological Society