COMMON BEAN (PHASEOLUS-VULGARIS L) MUTANTS DEFECTIVE IN ROOT-NODULE FORMATION .2. GENETIC-ANALYSIS

Genetic analysis of crosses between two induced, ineffectively nodulating mutants of common bean, NOD238 and NOD109, revealed that their mutated nodulation phenotype is under the control of the same locus in both mutants. The two mutants also resulted allelic for poor pod fertility, the other trait common to the mutants. F1 plants from crosses with their wild types nodulated effectively and had wild type pod fertility. Ineffective nodulation and poor pod fertility traits co-segregated in the F2 generation in which plants with the mutant nodulation and pod fertility phenotypes represented 12.5% of the total population. Analysis in F3 confirmed that these plants were homozygous for both mutated characters. The results indicated both mutant traits studied are determined by a single recessive allele, named sym-2, whose inheritance is negatively affected by its pleiotropic effect on pod fertility determining a deficit of ineffectively nodulating combinations. In an allelism test with the non-nodulating mutant of common bean NOD125 it was found that ineffective nodulation is controlled at a different locus and that the two loci are not linked.