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 reported within only a few legume species. Inheritance of nonnodulation in 10 sweetclover (Melilotus alba Desr.) mutants was determined from F1, F2, and F3 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 F1 and F2 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.