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Pesticidally resistant rhizobium and agronomic use thereof
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Inventors: Alexander, Martin; Odeyemi, Oluwasuyi;
Assignee: Cornell Research Foundation, Inc. (Ithaca, NY)
Primary Examiner: Wiseman; Thomas G.
Assistant Examiner:
Attorney, Agent or Firm: Jones, Tullar & Cooper
This invention relates to Rhizobium strains having good infecting and nitrogen-fixing characteristics and which are resistant to fungicides. These strains are produced by cultivating a Rhizobium strain sensitive to a particular fungicide in the presence of an amount of the fungicide, and for a time less than that sufficient to kill the entire Rhizobium population but sufficient to kill a majority of the population. The remaining Rhizobium population is isolated and recultured in the presence of an increased amount of the fungicide, again an amount and a time less than sufficient to kill the entire Rhizobium population, but sufficient to kill a majority of the population. This procedure is repeated for sufficient passages, with increasing amounts of said fungicide, to provide a Rhizobium strain sufficiently resistant to said fungicide so that the Rhizobium strain multiplies and enters into a nitrogen-fixing symbiosis in the presence of agriculturally effective amounts of the fungicide. |
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DETAILED DESCRIPTION What is claimed is: 1.
A biologically pure culture of a fungicide resistant strain of Rhizobium, which strain has good infecting and nitrogen-fixing abilities in symbiosis with plants of the leguminosea family, prepared by a method which comprises: cultivating, in the presence of a Rhizobium-medium and an amount of a selected fungicide sufficient to kill at least 90% of the Rhizobium culture initially present, a culture of Rhizobium bacteria of selected strain and inoculation group having good infecting and nitrogen-fixing ability, whereby bacteria strains sensitive to said amount of said fungicide are killed; subjecting the residual fungicide resistant bacteria to at least one additional cultivation step, as above, in the presence of an increased amount of said fungicide; and recovering a Rhizobium strain having increased resistance to said fungicide; said fungicide being selected from agriculturally useful legume seed or soil fungicides which adversely affect the Rhizobium bacteria being cultivated.
Description:
STATE OF THE ART The importance in the humid tropics of nitrogen fixed symbiotically by Rhizobium in association with legume species is extremely great, as farmers still rely largely upon shifting cultivation as a major means of restoring and sustaining soil fertility and world fertilizer usage is small.
Even where fertilizers are available, a substantial proportion of N applied to soils is often unavailable to crops because of denitrification and leaching losses; these processes may even give rise to potential secondary problems of air and water pollution.
Besides, the energy-consuming, relatively inefficient chemical fixation of N by the Haber-Bosch process contributes only 2.
2.
times.
10.
sup.
10 kg/yr N to the global fixed N pool compared to 9.
1.
times.
10.
sup.
10 kg/yr provided by the more efficient, natural, biological N fixation (Hardy et al, "The Biochemistry of Nitrogen Fixation", Adv.
Chem.
Series No.
100:219-247, 1971).
It is in view of these fertilizer problems that many developing countries are currently considering the Rhizobium-legume symbiosis as a means of increasing crop yields and providing adequate plant proten without the input of costly and often unavailable fertilizer N
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