COMPARISON OF GROWTH AND N ACCUMULATION OF COMMON BEAN (PHASEOLUS-VULGARIS L) CV OAC RICO AND ITS 2 NODULATION MUTANTS, R69 AND R99

Nodulation mutants are present in many species of legumes and have pot ential as ideal reference crops in field measurements of N-2 fixation. The objective of this experiment was to characterize the growth, deve lopment, mineral-N accumulation, and N-2 fixation of two nodulation mu tants of common bean (Phaseolus vulgaris L.), R69 (nod(+)/fix(-)) and R99 (nod(-)) in comparison with the wild type parent OAC Rico. The mut ants were incapable of N-2 fixation. With dual dependence on N-2 fixat ion and NO3- as N sources, OAC Rico accumulated more N than R69 and R9 9. However, when supplied with mineral NO3- sufficient to prevent N-2 fixation in OAC Rico, its growth and N accumulation did not differ fro m those of the mutants. There were differences in internode length tha t resulted in different heights among the three lines. The addition of silver to the nutrient solution failed to restore nodulation to R99. As a result, it was determined that the nod(-) phenotype is not a resu lt of an ethylene-related mutation. The nodulation mutants R69 and R99 appear to be good choices as reference crops for common bean in N-2 f ixation studies.