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Regulation of Nodule Development in Supernodulating Mutants and Wild-Type Soybean

Dep. of Agronomy, Georgia Agric. Exp. Stn., Athens, GA 30602

^* Corresponding author.

Nodulation of soybean [Glycine max (L.) Merr.] is regulated factors both internal and external to the plant tissues. This greenhouse study was conducted to further characterize the regulating phenomena originating in the shoots and roots. Grafts were made among three genotypes, wild-type ‘Bragg’ and two supernodulating (nitrate-tolerant symbiotic: nts) mutants (nts 382 and nts 246) showed smaller root and shoot growth and greater nodulation than Bragg. In I-shaped grafts, one shoot of each genotype was grafted onto one mainstem of 7-d-old plants of each of the different root genotypes. In Y-shaped grafts, all possible two-way combinations of the shoots of the three genotypes were grafted onto two lateral branches of Y-shaped plants that developed after trimming the shoot apex. Varying the shoot genotypes in the I-shaped grafts resulted in significant (P < 0.05) differences in shoot dry weight, root dry weight, nodule number, nodule dry weight, and specific nodule activity, but varying the root genotypes had no effect. There were significant (P < 0.05) effects of shoot genotype on the plant dry weight and nodulation characters, and significant (P < 0.05) effects of root genotype on the nodule number in Y-shaped grafts. In both I-shaped and Y-shaped grafts, Bragg shoots increased partitioning of dry matter to the root tissue, whereas nts mutant shoots increased partitioning of dry matter to the nodule. A directional response of nodulation was present in Y-shaped grafts with greater nodulation occurring on the half of the root system corresponding to the supernodulating nitrate-tolerant shoots vs. Bragg shoots.

Received for publication May 24, 1990.