A supernodulating mutant isolated from soybean cultivar enrei

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Abstract
Symbiotic nitrogen fixation in nodules of legumes depends on the complex interaction between the legume plant and (Brady)Rhizobium bacteria. Nodule formation and nitrogen fixation are closely regulated by both the host plant and the microsymbiont. Plant mutants with altered symbiotic performance are considered to be useful to gain a better understanding of the plant—microbe interactions in the legume—(Brady)Rhizobium symbiosis (Jacobsen 1984; Carroll et al 1985a, b; Park and Buttery 1988; Duc and Messager 1989; Gremaud and Harper 1989). Recently, Carroll et al. (1985a, b) have isolated the supernodulating mutants of the soybean cv. “Bragg,” which display a very large number of nodules and “nitrate-tolerant-symbiotic” (nts) characteristics. More recently, Gremaud and Harper (1989) have also isolated similar mutants from the soybean cv. “Williams.” These mutants not only provide materials that are useful for investigatings on the interaction in the nodule formation processes but also for agricultural practice. In particular, the nitrate-tolerance of these supernodulating mutants (Carroll et al. 1985b; Gremaud and Harper 1989) is useful for their cultivation in Japan where the level of soil nitrogen in fields is generally high. However, the cultivars previously used for the isolation of these mutants cannot adapt easily in Japanese climate due to different Maturity Group. Therefore, we attempted to isolate mutants with altered symbiotic phenotypes from the soybean cultivar “Enrei,” one of the most common cultivars in Japan.