Effect of high temperature on plasmid curing of Rhizobium spp. in relation to nodulation of pigeonpea [Cajanus cajan (L.) Millsp.] |
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| Authors: | P K Sharma K Laxminarayana |
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| Institution: | (1) Department of Microbiology, Haryana Agricultural University, 125004 Hisar, India;(2) Present address: Lehrstuhl für Genetik, Universität Bielefeld, Postfach 8640, D-4800 Bielefeld, FRG |
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| Abstract: | Summary Fifty-six isolates of Rhizobium and Bradyrhizobium spp. (Cajanus) were studied for their plasmid profile and N2-fixation efficacy. One to three plasmids were reproducibly detected in all the Rhizobium spp. strains but no plasmid was detected in the Bradyrhizobium spp. strains. Rhizobium sp. strain P-1 was mutagenized by Tn5 and three nod– and six nod+fix– were screened for symbiotic parameters. Neomycin-sensitive mutants were isolated by elevated temperatrue (40°C) from tranconjugants carrying Tn5 insertions. The high temperature  cured these mutants from the single large plasmid present in the parent strain P-1. All these cured mutants were nod–, indicating that the genes for nodulation were present on this plasmid, which is readily cured at a high temperature (40°C). The high temperature in the semi-arid zones of Haryana could be responsible for the low nodulation of pigeonpea because the plasmid carrying the nodulation genes is cured at 40°–45°C giving rise to non-nodulating mutants. |
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| Keywords: | Bradyrhizobium spp Rhizobium spp Cajanus cajan Pigeonpea Acetylene reduction assay (ARA) Curing Nodulation Plasmid |
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