NITRATE REDUCTASE AND NITROGENASE ACTIVITIES OF COMMON BEANS (PHASEOLUS VULGARIS L.) FROM DIFFERENT GEOGRAPHIC LOCATIONS

Cultivars of Phaseolus vulgaris (L.) from contrasting geographic locations were cultivated under fields conditions for measurements of nitrogenase and nitrate reductase activities. A first trial with two cultivars indicated that a tropical cultivar B-789 has a higher nitrogenase activity than a temperate one Elsa. And the converse was true for the nitrate reductase activity. While where a post flowering application was made, a renewal of nitrate reductase activity occurred. Further similar comparisons of both enzymatic activities upon eight tropical and temperate cultivars of equivalent vegetative cycles indicated, on the average, that tropical cultivars have a higher level of (C₂H₂) reduction and a lower nitrate reductase activity than temperate cultivars. These observations suggest that there exists an inverse relationship between the two enzymatic activities in common beans, and there probably exists genetic variability for a possible improvement of N-fixation ability. An early application of N-fertiliser upon the Elsa and B-789 plots promotes later nitrogenase activity while a post flowering application shows obvious a renewal of nitrate reductase activity. Thus, analyses of nitrate reductase and nitrogenase activities of a common bean crop at different physiological stages may give us an indication of the best time to apply supplementary nitrogen fertilisation to common beans to increase seed yield.