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

The nodulation characteristics of soybean (Glycine max) mutant nts382 are described. The mutant nodulated significantly more than the parent cultivar Bragg in the presence and absence of several combined nitrogen sources (KNO(3), urea, NH(4)Cl, and NH(4)NO(3)). The number of nodules on the tap root and on lateral roots was increased in the mutant line. In the presence of KNO(3) and urea, nitrogenase activity was considerably higher in nts382 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 M(3) progeny derived from a M(2) 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 that have been proposed to explain nitrate inhibition of nodulation.