Identification of Salt Tolerant Chickpea Genotypes Based on Yield and Salinity Indices

Salinity is a serious obstacle in the arid and semi-arid tracts of the world that exerts its negative impact on the physiological behaviour of the plant by disrupting the osmotic and ionic equilibrium, photosynthesis, protein and lipid metabolism (Kumar et al., 2016; 2018a and Lata et al., 2019). In India, continuous use of poor-quality water in irrigation, expanded irrigation network and climate change are mainly responsible for increased salt affected areas, which are predicted to increase from the current 6.73 M ha to 16.2 M ha by 2050 (Sharma and Singh, 2015). Chickpea (Cicer arietinum L.), a cool season crop, is the largest produced food legume in South Asia and the third largest globally, after common bean and field pea. Besides having high protein content (20-22%), chickpea is also a rich source of fibres, minerals and b-carotene and many components in chickpea have been identified that possess antihypertensive, antioxidant and anticancer properties (Jukanti et al., 2012; Jayalakshmi et al., 2019; Juárez-Chairez et al., 2020). In addition to this, chickpea plays an important role in maintenance of the soil fertility by fixing atmospheric N up to 140 kg/ha through rhizobium symbiosis, particularly in the arid and low rainfall areas (Rupela and Rao, 1987; Roy et al., 2010). Although, chickpea is generally considered as salt sensitive crop (Mann et al., 2019), but large genotypic variations exist among chickpea genotypes (Turner et al., 2013). The available literature reported the negative effects of salinity stress on both the vegetative (Khan et al., 2015) and reproductive growth stage (Turner et al., 2013; Dudhe and Kumar, 2018) which ultimately hastens the yield (Kumar et al., 2017; Zorb et al., 2019; Pushpavalli et al., 2020). Keeping in view, an experiment was planned to identify salt tolerant genotypes based on yield and yield indices by giving saline irrigation of 6 dS/m and 9 dS/m at the critical stages of chickpea growth.

To evaluate the salt tolerance potential of chickpea, ten genotypes (CSG-8962, BG-1103, S7, DCP 92-3, ICCV-10, KWR-108, BG-256, K-850, JG-16 and ICC 4463) were sown in randomised complete block design with 3 replications in 20 kg clay/porcelain pots (30 × 28 cm; diameter × height) filled with acid washed sand in net house of Division of Crop Improvement, ICAR-Central Soil Salinity Research Institute, Karnal, Haryana, India during 2018-19 and 2019-20. Different treatments were applied through irrigation water i.e. best available water as control and saline water of 6 dS/m and 9 dS/m for salinity. The water properties have been depicted in Table 1. For saline irrigation, water collected from Nain (Panipat, Haryana) was diluted with best available water to 6 dS/m and 9 dS/m. Before sowing, 3.12 litres of water was applied with or without salt (equal to the pot field capacity). Seeds of each genotype were surface sterilized using 0.1% Bavistin and six seeds per pot were sown with three pots per replication for each genotype. CSG-8962 (Karnal Chana-1) was used as salt tolerant check. Further irrigation was given on alternate day with or without salt water as per treatment details along with Wilson and Reisenauer nutrient solution (Wilson and Reisenauer, 1963). The net house was covered with a high-quality transparent polythene sheet of 0.34 mm thickness (gauge number 29) to avoid Rainwater. The leachates were collected from time to time to monitor the buildup of the desired salinity. At harvest stage, yield and yield attributing traits were recorded on five randomly selected plants of each genotype for total number of pods, productive pods/filled pods, unfilled pods, yield/plant and 100 seed weight. Taking into consideration, different tolerance indices (Nouraein et al., 2013; Anwaar et al., 2020) based on yield were calculated to know the potential of chickpea genotypes against salinity stress viz. stress tolerance index (STI), stress susceptibility index (SSI), stress tolerance (TOL), yield stability index (YSI) and relative salinity index (RSI). Analysis of data was done by using two factorial RBD. For critical difference (CD), treatments and genotypes were compared using 5% level of significance with the help of SAS (Version 9.3, SAS Institute Inc., Cary, NC, USA).
 

Yield attributing traits
 
Field crops and their genotypes differ in their ability to grow and yield satisfactorily under salt stress conditions. Particularly, yield depends on the ability of the crops to assimilate and exploit the resources and, thus, is the interplay of many components contributing towards final harvest. Pods are the important photosynthetic organ that re-fixes respired carbon within the pod wall and translocate it to the developing seed (Leport et al., 2006). Maximum pods were developed when chickpea plants were irrigated with best quality water (EC- 0.6 dS/m and pH- 7.4) i.e. 52.5 pods/plant in JG 16 to 89.17 pods/plant (DCP 92-3) with mean value of 68.77 pods/plant. Saline irrigation water decreased the number of pods/plant by 21.29% under EC_iw 6 dS/m and 53.29 % under EC_iw 9 dS/m (Table 2). Under higher salinity of EC_iw 9 dS/m, maximum pods/plant was noted in ICCV 10 (44.33) and CSG 8962 (42.67), whereas genotypes S7, BG 256, ICC 4463 showed the lowest number of pods/plant (Table 2). Data regarding filled and unfilled pods also revealed the significant effect of salinity stress. Regarding filled pods, mean total of 66.02 pods were found under control conditions, which decreased by 31.13 % and 81.34 % at EC_iw 6 and 9 dS/m, respectively (Table 2). It was also noted that genotype ICCV 10, CSG 8962 and DCP 92-3 retained maximum number of filled pods at EC_iw 6 dS/m, while under higher salinity of EC_iw 9 dS/m, CSG 8962, ICCV 10 and KWR 108 had the highest filled pods (Table 2). Number of unfilled pods significantly increased with increasing salinity. Mean value of 2.75, 8.67 and 19.8 for unfilled pods were noted under control, EC_iw 6 dS/m and EC_iw 9 dS/m (Table 2). Pod formation has been reported the most sensitive stage under salinity stress that leads to high rate of pod abortion and tolerant genotype must have higher number of filled pods with higher seed number (Samineni et al., 2011; Vadez et al., 2012). The test grain weight (1000 seed weight) was also negatively impacted under salinity, with plants grown under salt treatment recording a reduction of 45.66% and 62.5% in 1000 seed weight, respectively compared to plants under non-saline conditions (Table 2). On mean basis, chickpea genotype S7 showed highest 1000 seed weight and ICC 4463 showed the lowest, respectively (Table 2). Salinity induced damage to reproductive tissues leading to reductions in number of total pods, filled pods and 1000 seed weight that was attributed to direct reduction of seed yield (Atieno et al., 2017; Raju Pushpavalli et al., 2015).
 

 
Grain yield
 
Chickpea genotypes showed significant variability in yield and it ranged from 28.73 to 56.62 g/plant, 14.13 to 27.32 g/plant and 0.42 to7.62 g/plant under controlled, EC_iw 6 dS/m and EC_iw 9 dS/m respectively. Under controlled condition, the maximum yield was noted in KWR 108 (56.62 g/plant) followed by DCP 92-3 (50.35 g/plant) and CSG 8962 (48.62 g/plant), whereas minimum yield was obtained in ICC 4463 (28.73 g/plant) (Fig 1). Stress occurrence before flowering caused reduction in photosynthesis sources, decrease in source to sink ratio that ultimately led to reduced grains number and weight (Kumar et al., 2017). In the present study also, saline water of 6 dS/m caused reduction of 36.1%-65.0% in grain yield, which further aggravated by irrigation saline water of 9 dS/m i.e. 81.0%-98.5% (Fig 1). Interestingly, in spite of having low yield under control condition, some genotypes showed lower reduction than the salt tolerant check CSG 8962 (46.9%) at EC_iw 6 dS/m viz. S7 (36.1%) and ICCV-10 (41.2%). While at EC_iw 9 dS/m, only one chickpea genotype S7 showed less reduction in grain yield than the salt tolerant check in comparison to their respective control (Fig 1). This reduction in grain yield with saline irrigation water could be due to early maturity (shrivelled grain) or inadequate photosynthetic source (Kumar et al., 2017; Sanwal et al., 2018) or it might possibly be due to decreased pollen viability and stigma receptivity of leading to poor seed setting, chaffy grains and reduced seed weight under stress conditions ultimately culminating in lower crop yields (Saini, 1997).
 

 
Yield indices
 
To fulfill our main objective, based on seed yield different tolerance indices (Nouraein et al., 2013; Anwaar et al., 2020) viz. stress tolerance index (STI), stress susceptibility index (SSI), stress tolerance (TOL), yield stability index (YSI) and relative stress index (RSI) were calculated to know the potential of chickpea genotypes against salinity stress of EC_iw 6 dS/m (Table 3) and EC_iw 9 dS/m (Table 4). Chickpea genotypes showed statistically significant (p<0.001) difference for stress indices and ranked accordingly. Based on STI value, KWR 108 was ranked first under EC_iw 6 dS/m and EC_iw 9 dS/m followed by genotype CSG 8962, while genotype ICC 4463 ranked last under both the stress condition (Table 3 and 4). SSI values were maximum in BG 256 and DCP 92-3 (1.24), while genotype S7 showed the minimum SSI value at EC_iw 6 and 9 dS/m (Table 3 and 4).  At EC_iw 6 dS/m, highest tolerance was shown by genotype S7 followed by KWR 108 (Table 3) while at EC_iw 9 dS/m, KWR 108 showed maximum tolerance (Table 4). YSI and RSI values were highest in genotype S7 under both the stress condition, while BG 256 and ICC 4463 showed the lowest YSI and RSI at EC_iw 6 dS/m and EC_iw 9 dS/m, respectively (Table 3 and 4).
 

 

 
Association between grain yield and salinity indices
 
Correlation of grain yield with different stress indices at EC_iw 6 and 9 dS/m was strong to weak depending upon the type of stress indices and salinity level. The stress tolerance index is highly and positively correlated with grain yield at both the salinity levels except control at EC_iw 9 dS/m have weak correlation (Fig 2A and 2B). Stress susceptibility index had a weak positive correlation with grain yield in control and stress at EC_iw 6 dS/m but at stress level of 9 dS/m, the correlation was highly and positively correlated with grain yield suggesting selection of best material under stress condition (Fig 2C and 2D). Stress tolerance had a significant positive correlation in controlled condition at both the levels of salinity but weak correlation under stress (Fig 2E and 2F). Yield stability index and relative stress tolerance had a weak positive correlation with grain yield at control and stress condition of EC_iw 6 dS/m but at 9 dS/m the control had weak positive correlation while stress has a strong positive correlation with grain yield (Fig 2G, 2H, 2I and 2J).
 

Based on yield and salinity stress indices, it can be concluded that genotypes S7 and KWR 108 were having higher salt tolerance than salt tolerant check variety CSG 8962 at moderate and extreme salinity stress of EC_iw 6 dS/m and EC_iw 9 dS/m, whereas   BG 256 and ICC 4463 were the most sensitive chickpea genotypes.

The authors are thankful to  Director or ICAR-CSSRI, Karnal and Head, Division of Crop Improvement for providing necessary facilities to carry out the research work.

The authors declare no conflict of interest among them.