Interactive Effects of Salinity and Biological Nitrogen Fixation on Chickpea (Cicer arietinum L.) Growth

Abstract

The effect of salinity on the nodulation, N-fixation and plant growth of selected chickpea-Rhizobium symbionts was studied. Eighteen chickpea rhizobial strains were evaluated for their growth in a broth culture at salinity levels of 0 to 20 dS m(-1) of NaCl + Na2SO4. Variability in response was high. Salinity generally reduced the lag phase and/or slowed the log phase of multiplication of Rhizobium. Nine chickpea genotypes were also evaluated for salt tolerance during germination and early seedling growth in Petri dishes at five salinity levels (0-32 dS m(-1)). Chickpea genotypes ILC-205 and ILC-1919 were the most salt-tolerant genotypes. The selected rhizobial strains and chickpea cultivars were combined in a pot experiment aimed at investigating the interactive effect of salinity (3, 6 and 9 dS m(-1)) and N source (symbiosis vs. inorganic N) on plant growth. Symbiotic plants were more sensitive to salinity than plants fed mineral N. Significant reductions in nodule dry weight (59.8%) and N-fixation (63.5%) were evident even at the lowest salinity level of 3 dS m(-1). Although nodules were observed in inoculated plants grown at 6 dS m(-1), N-fixation was completely inhibited. The findings indicate that symbiosis is more salt-sensitive than both Rhizobium and the host plant, probably due to a breakdown in one of the processes involved in symbiotic-N fixation. Improvement of salinity tolerance in field grown chickpea may be achieved by application of sufficient amounts of mineral nitrogen.