Inheritance of Nonnodulating Mutants of Sweetclover

Legume mutants defective in nodule formation are useful for understanding interactions between host and bacterium. Nonallelic nodulation mutants have been relmrted within only a few legume species. Inheritance of nonnodulation in 10 sweetclover ( Melilotus alba Desr.) mutants was determined from F 1 , F 2 , and F 3 generations derived from crosses between each mutant and the nodulating accession U389. Nonnodulation in each mutant was conditioned by a single recessive gene. Complementation analysis was performed on F 1 and F 2 seedlings derived from diallel crosses among the mutants. Five of the mutants were nonallelic, indicating that at least five different genes are involved in nodule formation in M. alba . The following symbols are proposed for the genes controlling nonnodulation of these sweetclover mutants: sym‐1, sym‐2, sym‐3, sym‐4 , and sym‐5 .