A Supernodulation and Nitrate-Tolerant Symbiotic (nts) Soybean Mutant

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Abstract
The nodulation characteristics of soybean (Glycine max) mutant nts382 are described. The mutant nodulated significantly more than the parent cv Bragg in the presence and absence of several combined N sources (KNO3, urea, NH4Cl and NH4NO3). The number of nodules on the tap root and on lateral roots was increased in the mutant line. In the presence of KNO3 and urea, nitrogenase activity was considerably higher in n4ts382 than in ''Bragg''. Mutant plants were generally smaller than wild-type plants. Although nts382 is a supernodulator, inoculation with Rhizobium japonicum was necessary to induce nodule formation and both trial strains CB1809 (= USDA136) and USDA110 elicited the mutant phenotype. Segregation of M3 progeny derived from a M2 wild-type plant indicated that the mutant character is inherited as a Mendelian recessive. The mutant is discussed in the context of regulation of nodulation and of hypotheses proposed to explain NO3- inhibition of nodulation.