Shoot control of nodulation is modified by the root in the supernodulating soybean mutant En6500 and its wild-type parent cultivar Enrei

Based on grafting studies, both supernodulating (Carroll et al. 1985a, b) and hypernodulating (Gremaud and Harper 1989) soybean ([itGlycine max} L. Merr.) phenotypes were reported to be under the control of shoot factors (Delves et al. 1986, 1987; Cho and Harper 1991). Recently Akao and Kouchi (1992) have isolated a new supernodulating mutant (En6500) from ethyl methane sulfonate (EMS)-treated Enrei, a cultivar which is widely grown in the central districts of Japan. This mutant has been shown to produce several fold as many nodules as its wild-type parent cultivar when grown at a low concentration (0.5 mol m-3) of nitrate. Moreover, it exhibited a continuous increase in the nodule number with the increasing nitrate concentration, even at 15 mol m-3 (Francisco et al. 1992), in contrast to the similar mutant nts382 in which the nodulation decreased even at the relatively low nitrate level of 5.5 mol m-3 (Carroll et al. 1985a). In this study we conducted grafting experiments to determine which plant part controls the supernodulation of En6500.