SHOOT-ROOT CONTROL OF NITRATE TOLERANCE OF N-2 FIXATION IN SPONTANEOUSLY TOLERANT SOYBEAN LINES - RECIPROCAL GRAFTING EXPERIMENTS

A characterization of spontaneous nitrate tolerance of nitrogen fixati on in soybean was carried out by means of 2 reciprocal grafting experi ments, with a top cross and a diallel type design. Shoot-root control of nitrate tolerance was studied in a spontaneous tolerant line (Tieli ngbaime), a non-tolerant cv (Kingsoy), and 5 progeny lines derived fro m their cross. Both experiments demonstrated a shoot control for nitra te tolerance of nodulation. Nitrate tolerance was expressed as the mai ntenance of a higher number and la greater specific mass of nodules in the presence of nitrate. Regulation of nitrogen fixation in the prese nce of nitrate also seemed to be related to shoot factors. However, di allel analysis of reciprocal grafts indicated that interaction effects with root control could not be excluded for this trait.