Genes Controlling Nodulation in Soybean: Rj₅ and Rj₆

A number of genes have been identified that affect root nodule formation in soybean [ Glycine max (L.) Merr.] when inoculated with Bradyrhizobium japonicum (Kirchner) Buchanan. The non‐nodulating mutant, NN5, used in this study was isolated from N ‐nitroso‐ N ‐methylurea mutagenized ‘Williams’ seed. The objectives of this study were to determine the number of genes responsible for non‐nodulation in NN5 and the relationship between the genes in NN5 and the other known non‐nodulation genes. From this study it was found that non‐nodulation genes in NN5 were not allelic to the rj 1 gene. One of the genes responsible for non‐nodulation in NN5 was allelic to the previously identified, but unnamed single recessive gene found in nod139, a non‐nodulating mutant of ‘Bragg’. A second recessive gene controlling non‐nodulation was identified in NN5 when crosses were made with ‘Harosoy 63’. Harosoy 63 was shown to contain a non‐allelic dominant gene that conditions nodulation when in combination with the gene found in nod139 and NN5. The gene symbol Rj 5 is given to this new nodulation gene found in Harosoy 63, and the symbol rj 6 is given to the allelic gene conditioning non‐nodulation in nod139 and NN5. Several other cultivars, Williams, Williams 82, Chapman, Resnik, and Chamberlain, do not contain the dominant gene Rj 5 .