Effect of NaCl Salinity on the Growth and the Nitrogen Status of Nodulated Cowpea (Vigna sinensis L.) and Mung Bean (Phaseolus aureus L.)

Abstract

Plants of V. sinensis and P. aureus were grown in the presence of five levels of NaCl ranging from 10 to 100 mM. V. sinensis grew better than control plants in the presence of NaCl even up to 75 mM, while P. aureus showed a decline in its growth even at 10 mM NaCl concentration. Nodulation of V. sinensis by Rhizobium cowpea strain no. 3200 occurred up to a salt concentration of 100 mM NaCl. When P. aureus was infected with Rhizobium japonicum strain no. G49, nodulation did not occur in the plants growing with more than 25 mM NaCl. Successful nodulation of both species in the presence of NaCl was associated with some kind of salt tolerance either of the host plant or of the Rhizobium partner. Cowpea rhizobium strain no. 3200 was found to tolerate the NaCl salinity better than R. japonicum strain no. G49. Total nitrogenase activity estimated by the amount of N fixed during the growing period was found to be positively correlated with NaClext application up to 75 mM in V. sinensis. However, this result was difficult to correlate with the ARA of the nodules measured at harvest. In contrast, salt application had a negative effect on N fixation by P. aureus.