GENOTYPIC DIFFERENCES IN NITROGEN ASSIMILATION IN VICIA-FABA - EFFECTOF NITRATE

Five inbred lines and a commercial cultivar of field-bean (Vicia faba) were inoculated with a strain of Rhizobium leguminosarum by. viciae a nd grown, with or without nitrate, under axenic conditions in a growth chamber. There were significant (p < 0.01) differences between lines in N yield, both in N-free solution (N2 fixed, fully symbiotic) and wi th added NO3-. Increase in the N yield of NO3--fed plants compared wit h fully symbiotic plants also varied between genotypes, with line VF10 9 being the least responsive to NO3-. This may indicate nitrate tolera nce in relation to N2 fixation. The indication was supported by the ob servations that nodule development and nodule activity (acetylene redu ction) were less inhibited in VF109 in the presence of 8 mM NO3- than in the other lines of Vicia faba. Glutamine synthetase and glutamate s ynthase (GOGAT) activities appeared to be related to genotypic differe nces in symbiotic efficiency. This finding suggests that assays of nod ule glutamine synthetase and NADH-glutamate synthase might be used in Vicia faba breeding programs to indicate capacity for symbiotic N2 fix ation, particularly in the presence of NO3-.