EFFECTS OF NITROGEN, INOCULATION AND GRAFTING ON EXPRESSION OF SUPERNODULATION IN A MUTANT OF Phaseolus vulgaris L.

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Abstract
A supernodulating mutant of Phaseolus vulgaris L. grew much like its parent line OAC Rico, but plant weights were significantly lower at 26 and 39 d after seeding. Between these sampling dates relative growth rate was greater in the supernodulator than in OAC Rico. Both parent and mutant responded to combined nitrogen by increases in plant weight. Continuous treatment with 14 mM combined N severely reduced nodulation of the mutant as well as OAC Rico whereas 2.1 mM and 14 mM discontinued after 10 d stimulated nodule mass in the mutant. Specific nodule activity (acetylene reduction) was lower in the mutant than OAC Rico. Leaf nitrate reductase activity was similar in both. In the absence of Rhizobium, but with 2.1 and 14 mM combined N, the mutant and OAC Rico grew similarly. Reciprocal grafting of shoot and root between the mutant and OAC Rico established that the supernodulating characteristic was controlled by the shoot.Key words: Acetylene reduction, grafting, nitrate reductase, Rhizobium, supernodulation, bean (common; field)