PHYSIOLOGY OF CHICKPEA (Cicer arietinum L.) UNDER SALT AND HIGH TEMPERATURE STRESS CONDITION
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Date
2021
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Dr.RPCAU, Pusa
Abstract
Chickpea is the third most important legume crop after pea and soybean. India ranks first in terms of area and production of chickpea globally. Chickpea is a source of high-quality protein along with essential nutrients like iron, zinc and phosphorus among others. Chickpea being a legume crop is a potent contributor in improvement of soil fertility by having the ability to fix atmospheric nitrogen in plant-available form through developing interaction with symbiotic micro-organisms like Rhizobium in their root. Thus, chickpea has a great potential in attainment of the most important talk of the hour- agricultural sustainability. Despite of having so much importance in agriculture and also great nutritional value, chickpea production has not been growing since decades as per the demand. There may be a number of factors relying behind this fact. Plants have to go through many stressful situations throughout their life cycle. Some of these stress factors are biotic and some are abiotic. All these stress factors bring a number of deteriorative effects on plants.
Among the abiotic stress factors, salinity and high temperature are very important. Nowadays, these two stresses are highly being discussed for their negative impacts on crops. Chickpea is highly sensitive to both salinity and high temperature at seedling and reproductive stage. A number of previously done research works is available denoting the harmful effects of salinity and high temperature in individual
condition on crops, but the effects of combined salinity and high temperature stress on crops are hardly available, especially on chickpea. So, keeping this view in mind, an experiment was undergone with thirty chickpea genotypes with the purpose of screening and identifying contrasting sets of chickpea genotypes against combined salt and high temperature stress based on physiological traits in laboratory condition. In this objective, three most tolerant (KPG-59, IPC-2013-74 and NDG-15-6) and three most susceptible genotypes (KWR-108, BG-3075 and BG-3076) were selected based on growth parameters viz. germination percentage (GP), germination relative index (GRI), seedling length (SL), vigour index-I (VI-I), seedling dry weight (SDW), vigour index-II (VI-II); and stress tolerance indices such as tolerance index (TOL) and yield stability index (YSI) in 10-day-old seedlings.
The next objective was to further study physiological and biochemical changes occurring in those six screened genotypes (in leaf) at pod formation stage; and nutritional parameters (Na, K, Zn and Fe) in seed after harvesting for those six screened genotypes sown in pots at normal soil (0.40 dSm-1) for control, saline soil (4.20 dSm-1) for salt stress, at normal soil (EC = 0.40 dSm-1 and ECe = 1.50 dSm-1) with delayed sowing for high temperature stress, and at saline soil (EC = 4.20 dSm-1 and ECe = 7.40 dSm-1) with delayed sowing for combined stress in two experimental years 2019-20 and 2020-21. From this experiment, it was observed that H2O2 content MDA content increased while MSI decreased. Other physiological parameters such as RWC, photosynthetic pigments (chl a, chl b, total chl content and carotenoids content), CSI and SPAD unit decreased with stress over control; however, relatively lesser percentage decrease was observed for the tolerant genotypes as compared to the susceptible genotypes for both the experimental years 2019-20 and 2020-21. Among biochemical parameters starch content, total soluble sugar content and total soluble protein content decreased; while proline content, total amino acids content, phenol content increased in response to individual and combined salt and high temperature stress. Antioxidant enzymes determined in this experiment viz. SOD, POX and CAT increased broadly for all the genotypes when exposed to stress treatments, especially under combined stress. Nutritional parameters also expressed a wide genotypic range over the treatments. Sodium and potassium contents increased as opposed to zinc and iron contents in chickpea seeds.
The last experiment was based on determination of yield and yield attributes. Days to 50% flowering decreased widely along with the number of branches plant-1.
Number of pods plant-1, number of seeds pod-1, seed yield, seed test weight and harvest index severely decreased under all the stress treatments, with more pronounced effects under combined stress denoting the fact that plants when come under more than a single stress at a time, get affected at a greater rate.
Increase in lipid peroxidation represented the effect of stress on chickpea plants for which plants have recorded with decline in physio-biochemical parameters. The decrease in starch content, total soluble sugar content, reducing sugar content and non-reducing sugar content could be related with lesser photosynthetic rate in chickpea plants under different stress treatments as compared to the control condition. Chickpea genotypes responded in counter with developed tolerance to salt and high temperature stress by increased proline and amino acid content; and improved activities of antioxidant enzymes viz. SOD, POX and CAT. The reduction in yield and yield attributes under salinity and high temperature could be attributed to the stress-induced retarded reproductive growth resulting in reduced pod numbers in individual plant, reduced seed numbers in each pod, and decreased seed yield due to reduced seed size.
Seed yield was compared with other physiological, biochemical and yield governing traits through Pearson’s Correlation Matrix. A number of physiological traits like MSI, RWC and total chlorophyll were found to be positively correlated; and MDA was found negatively correlated with seed yield under various treatments used in this experiment. Significant correlation with biochemical parameters was also observed among which starch, total soluble sugar and total soluble protein built up positive correlation; and phenol, amino acids and proline built up negative correlation. Yield attributing traits such as number of pods plant-1, seeds pod-1, seed test weight and HI were highly significant and in positive correlation with seed yield.