| Abstract: | Two ineffectively nodulating, allelic mutants of the commonbean (Phaseolus vulgaris L.) lines RIZ30 and RIZ36 were studied.In both mutants the nodulation phenotype was characterized bythe formation of tumour-like swellings when inoculated withbean Rhizobium strains. Late formation of pink nodules was observedin mutant plants grown in pots with soil or in hydroponic conditionswith perlite. In the absence of mineral nitrogen, mutant growthand nodulation were poor; a low peak of acetylene reductionactivity being detected 45 d after inoculation. Mutant growthin the presence of mineral nitrogen was similar to that of thewild type. The mutants were also characterized by poor pod fertility(seed per pod). The nodulation and pod fertility phenotypesare specifically controlled at the root and shoot levels, respectively,as assessed with grafting experiments. Mutant shoots graftedon wild type, nitrogen-fixing roots produced a number of seedssimilar to the wild type despite the expression of the poorpod fertility phenotype. Nitrogen and seed yields of wild typeshoots, grafted on mutant, ineffectively nodulating roots wereseverely reduced when compared with control wild type plantsalthough nitrogen accumulation during vegetative phase was similar. Key words: Phaseolus valgaris, nitrogen fixation, nodulation mutants, grafting, nitrogen assimilation |
