Comparison of growth and N accumulation of common bean (Phaseolus vulgaris L.) cv. OAC Rico and its two nodulation mutants, R69 and R99

Abstract

Nodulation mutants are present in many species of legumes and have potential as ideal reference crops in field measurements of N2 fixation. The objective of this experiment was to characterize the growth, development, mineral-N accumulation, and N2 fixation of two nodulation mutants of common bean (Phaseolus vulgaris L.), R69 (nod+/fix-) and R99 (nod-) in comparison with the wild type parent OAC Rico. The mutants were incapable of N2 fixation. With dual dependence on N2 fixation and NO3- as N sources, OAC Rico accumulated more N than R69 and R99. However, when supplied with mineral NO3- sufficient to prevent N2 fixation in OAC Rico, its growth and N accumulation did not differ from those of the mutants. There were differences in internode length that 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 result of an ethylene-related mutation. The nodulation mutants R69 and R99 appear to be good choices as reference crops for common bean in N2 fixation studies.