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

Genetic analysis of crosses between two induced, ineffectively nodulat ing mutants of common bean, NOD238 and NOD109, revealed that their mut ated nodulation phenotype is under the control of the same locus in bo th mutants. The two mutants also resulted allelic for poor pod fertili ty, the other trait common to the mutants. F1 plants from crosses with their wild types nodulated effectively and had wild type pod fertilit y. Ineffective nodulation and poor pod fertility traits co-segregated in the F2 generation in which plants with the mutant nodulation and po d fertility phenotypes represented 12.5% of the total population. Anal ysis in F3 confirmed that these plants were homozygous for both mutate d characters. The results indicated both mutant traits studied are det ermined by a single recessive allele, named sym-2, whose inheritance i s negatively affected by its pleiotropic effect on pod fertility deter mining a deficit of ineffectively nodulating combinations. In an allel ism test with the non-nodulating mutant of common bean NOD125 it was f ound that ineffective nodulation is controlled at a different locus an d that the two loci are not linked.