Assessment of Photosynthetic Traits of Kabuli-type Chickpea Genotypes under Salinity Stress

The effect of salinity stress on the quantity and quality of crop production highlights the importance of managing and reducing the damage caused by this stress factor in agriculture. Increasing soil salinity and decreasing fertility of arable lands is one of the major problems in saline areas. Cultivation of salt-tolerant crops which can increase soil fertility could be effective in the sustainable production of these lands. Studying photosynthesis and its related factors could provide appropriate physiological views in understanding plant behavior against salinity stress. The present study was conducted to assess the salinity tolerance of chickpea genotypes for cultivation in saline areas.

To evaluate the effects of salinity stress on photosynthetic criteria and yield of chickpeas, an experiment was conducted in 2018 at the research farm of the faculty of agriculture, Ferdowsi University of Mashhad, Mashhad, Iran. The experiment was arranged as a split plot based on a randomized complete block design with three replications. Experimental factors consisted of salinity levels (0.5 and 8 dS.m-1) as the main plot and chickpea genotype (17 kabuli-type genotypes) as the subplot. Seeds were provided from the Mashhad chickpea collection of the Center for Plant Sciences, Ferdowsi University of Mashhad, Mashhad, Iran. Seeds were planted on March 11th and complementary irrigation was done in three growth stages of pre-flowering, flowering, and pod-filling. Sodium chloride was used to prepare saline solutions and the irrigation water rate was measured by water meter. Photosynthetic criteria including photosynthesis rate, evapotranspiration, stomatal conductance, and resistance and concentration of photosynthetic pigments were measured in the 50% flowering stage.

Results indicated that the lowest and highest reduction in the concentration of chlorophyll a was found in MCC65 (6%) and MCC83 (3.3 times increase), respectively. Increasing salinity level increased the concentration of chlorophyll b in MCC65 and MCC139, the ratio of chlorophyll a/b in MCC92, MCC139, and MCC776, carotenoids concentration in MCC77, MCC92, MCC313, and MCC679 and total pigments in MCCMCC77, MCC92, MCC298, and MCC679. Increasing salinity levels led to higher evapotranspiration in 14 genotypes except for MCC65, MCC95, and MCC298 in which 37, 54, and 63% decrease of this parameter was observed. Increasing salinity level increased photosynthesis rate in 7 genotypes of MCC12, MCC65, MCC72, MCC92, MCC95, MCC679 and MCC776 among which MCC95 and MCC679 showed the highest percentage increase (61 and 53%, respectively). The highest increase in sub-stomatal CO2 (51, 49, and 40 ppm) with increasing salinity levels, was found in MCC485, MCC776, and MCC313, respectively. An increase of 28 and 8% in stomatal conductance was found in MCC65 and MCC95. Stomatal resistance was only reduced in MCC77, MCC420, and MCC29. Higher salinity levels also led to 3.4 times, 67, 14, and 13% increase in instantaneous water use efficiency in MCC95, MCC65, MCC92, and MCC298, respectively. Biomass and seed yield declined in all genotypes by salinity. The highest seed yield was observed in MCC65, MCC77, MCC92, and MCC95 with 142, 148, 167, and 166 g.m-2 respectively in saline conditions. There was a negative significant correlation between seed yield and evapotranspiration (r=-0.43**), and stomatal resistance (r=-0.38**), and a significant positive correlation between seed yield and biomass (r=0.61**) and photosynthesis (r=0.24**) and stomatal conductance (0.36**).

In general, the results of this experiment indicated the diversity among chickpea genotypes for salinity tolerance caused by saline irrigation water. Studying some photosynthetic criteria in 17 kabuli-type chickpea genotypes under salinity stress showed high diversity in physiological responses of chickpeas to salinity stress which could be used in the selection and breeding of salt-tolerant cultivars. MCC65, MCC77, MCC92, and MCC95 were superior in most studied criteria in saline conditions and even performed, unlike the declining trend of the other genotypes. It seems that these genotypes could produce reasonable seed yield in salinity levels up to 8dS.m-1.