Nitrate levels and stages of growth in hypernodulating mutants of Lupinus albus. I. N-2 fixation potential

This work aimed to evaluate physiological parameters, nodulation response a nd N-2 fixation rate in mutants of Lupinus albus in comparison with the sta ndard Multolupa cultivar. Two nitrate levels (0 and 5 mM) and two evaluatio n periods (7 and 10 weeks) were used. Significant differences were observed among genotypes, in relation to fresh nodule weight, nitrate levels and gr owth stages. The overall average for nitrate level differed between them wh ere 5 mM severely inhibited the number of nodules, reaching a 49.5% reducti on in relation to treatment without nitrate. There were no behaviour differ ences among genotypes, nor among evaluation periods. Although the level of nitrate did not influence the production of shoot dry matter in relation to the average among levels applied, the L-135 genotype, being an inefficient mutant, reached very low values. There were no significant differences in electron allocation coefficient (EAC) among nitrate levels, nor among genot ypes studied. However, the evaluation periods revealed differences, where t he EAC for the seventh week had a higher value than that for the tenth week , when a 5 mM aplication was evaluated. The N-2 fixation rate (N-2 FIX) sho wed the existence of the nitrate interference in fixation, given that the a pplication of 5 mM severely reduced. However, there were no differences amo ng the genotypes and it was noted that the fixation rate was much higher in those that received nitrate. The L-88 and L-62 genotypes were the ones tha t have shown best adaptability in this experiment, thus being able to be re commended for new studies with higher nitrate levels and different evaluati on periods. The nitrate (5 mM) interferes in the nitrogen fixation rate, gi ven that all the genotypes were affected by the level applied.