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Prevention of Soybean Root Nodulation by Tetracycline and Its Effect on Soybean Root Rot Caused by an Alfalfa Strain of Fusarium oxysporum. J. C. Tu, Research Station, Agriculture Canada, Harrow, Ontario, Canada, N0R 1G0; Phytopathology 68:1303-1306. Accepted for publication 25 March 1978. Copyright © 1978 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-68-1303.

Tetracycline at or above 40 μg/ml was shown to be bactericidal to Rhizobium japonicum. In contrast, colony growth of Fusarium oxysporum from alfalfa was little affected by tetracycline at concentrations as high as 160 μg/ml. Soybean plants grown in soil containing R. japonicum and F. oxysporum were watered twice daily with 250 ml of Hoagland’s solution containing tetracycline at 160 μg/ml of solution. Soybeans grown in the tetracycline-treated soil were not nodulated and were only minimally affected by the drug treatment. Even in the absence of nodulation, soybeans were infected with F. oxysporum; Fusarium root rot was more severe in the plants grown in the tetracycline-treated soil than in those grown in the non-treated soil. The results confirmed previous observations that inoculation with rhizobia reduces the severity of root rot in soybeans and that infection of soybean roots by F. oxysporum may develop independent of root nodulation.