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Rhizobium meliloti populated in five Korean pasture soils were characterized by symbiotic effectiveness and intrinsic antibiotic resistance using whole-soil inoculum and 11 antibiotics, respectively. Most probable number (MPN) of naturalized rhizobia counted with alfalfa Vernal[Medicago sativa (L.)] as a host ranged 1.7×10² cells/g. soil(Chunghyo, Kyeongju)-l.0×10^5 cells/g. soil(Gampo, Kyeongju) and trended to be positively associated with soil pH. On the whole, the effectiveness of population as compared to TAL mix inoculum (TAI. 380＋TAL 1372＋TAL 1373) was very low. Nevertheless, there were two highly effective strains, YCK 539 and YCK 542, which were not inferior to TAL 1372, from Ogpo, Dalseong among the total of 30 of 6 isolates per each soil. As long as mean N₂ fixing ability of each soil isolate, the isolates from Hyeongog, Kyeongju were outstanding and the rest were in order of Ogpo, Dalseong$gt;Chunghyo, Kyeongju$gt;Hwaweon, Dalseong$gt;Gampo, Kyeongju. Isolates as a whole were resistant to eoythromycin(67%), nalidixic acid(77%), and streptomycin sulfate(80%), which had the concentration of 100 ㎍/㎖, 160 ㎍/㎖, and 10 ㎍/㎖, respectively and divided into 14 patterns of resistance. Association between resistances in each soil was not clear. And there was no relationship of resistance pattern to effectiveness. The best effective strain YCKa 542 exclusively fell into No. X pattern having resistance to erythromycin, nalidixic acid, and neomycin sulfate.
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