STUDIES ON THE ROOT CONTROL OF NON-NODULATION AND PLANT-GROWTH OF NONNODULATING MUTANTS AND A SUPERNODULATING MUTANT OF SOYBEAN (GLYCINE-MAX (L) MERR)

Ethyl methanesulphonate mutagensis of soybean cv. Bragg led to the isolation of three non-nodulating mutants: nod49, nod772 and nod139, as well as the supernodulation mutant nts382. Mutants nod49 and nod772 are allelic to the naturally-occurring mutation rj1 while nod139 is non-allelic and represents a newly found gene conditioning non-nodulation in soybean. Using the standard reciprocal wedge grafting technique it was shown earlier that non-nodulation in mutant nod49 is root controlled and supernodulation in mutant nts382 is shoot controlled. Non-nodulation in mutants nod772 and nod139 (the newly found non-nodulation gene in soybean) is also root controlled. In addition, scions of nts382 failed to alter the nodulation phenotype when grafted onto stocks of the non-nodulating lines. Lateral roots developing from the scion of nts382 and Bragg exhibited supernodulation and the wild-type pattern of nodulation, respectively, indicating that the lesion(s) conditioning non-nodulation only affect the root in a localized manner. Physiological studies conducted on the mutants indicate that they are not altered in the assimilation of nitrogen and carbon when grown on nitrate, and a study of their nitrogen contents indicate that the anomaly in the non-nodulation mutants is clearly specific for the nodulation process. This was confirmed by assaying nitrate reductase (NR) under a range of conditions; it was observed that the non-nodulation mutants expressed inducible NR and constitutive NR activity in a manner similar to the wild type.