Biochemical analysis
The analysis of variance presented in Table 2 clearly indicated existence of substantial amount of variations among 60 soybean genotypes included in the present study for all biochemical parameters investigated. Chlorophyll is the core photosynthetic pigments that decide biomass of plants. Generally, the magnitude of chlorophyll content in leaves regulates the rate of photosynthesis. Drought stress constrains the photosynthesis by means of instigating alterations in chlorophyll content. Total Chlorophyll content in mg/ml varied significantly in range of 36.58-58.33 mg/ml in present investigation, maximum with genotype RVS 2011-75 while the minimum was in JS20-53*JS20-34.
Anjum et al., (2011) displayed a decline in the quantity of chlorophyll because of forfeiture of chloroplast membranes in drought susceptible genotypes. Analogous reduction in chlorophyll levels in many other plant species as well as soybean
(Zhang et al., 2007; Mishra et al., 2021c), chickpea
(Sahu et al., 2020) and peal millet
(Choudhary et al., 2021).
Soluble sugars are the key osmotic modification constituents and therefore are significant pointers of tolerance/resistance in genotypes. Total sugar in mg/g varied significantly in range of 2.4-5.9 mg/g with maximum in genotype RVS2011-77 trailed by genotypes RVS2011-73 and RVS 2011-10, while the minimum was perceived in genotype CAT87 and JS335 tracked by genotype PK885. Genotypes pursuing higher sugar content might be drought tolerant as reported earlier by
Kachare et al., (2019) and
Mishra et al., (2021c). The augmentations in MSI designate the lessening of lipid peroxidation with oxidative bursts under water stress conditions. Genotype PS1611 exhibited maximum membrane stability (MI) tracked by genotypes
viz., JS20-90 and JSM240*SL517 whereas, it was displayed by genotype AMS-MB 5-18 intimately pursued by genotypes Hardee and Gaurav.
Proline is trusted as an authoritative drought tolerance pointer. Proline content in μg/g varied meaningly between 65.31-107.27ìg/g with utmost in genotype EC 602288 (107.27) followed by genotypes JS97-52 (105.45), EC538828 (101.88) and NRC7 (100.25), more than 100μg/g. However, the minimum was observed in genotype JS2009*PS1475 (65.31) trailed by genotypes JS2063*JS95-60 (67.63) and SL 525 (67.9). Genotypes exhibiting higher proline content may have drought tolerance as suggested by
Kachare et al., (2019) and
Mishra et al., (2021c) as they also concluded during their study on screening of soybean genotypes. It may be perhaps due to increased proline content maintains cell water level under drought
(Choudhary et al., 2021).
Cluster analysis of different biochemical parameters (Total chlorophyll content, proline content, total sugar and MSI)
On the basis of dendrogram (Fig 1), genotypes formed two clusters. Major cluster consisted 53 genotypes while minor cluster had only 7 genotypes including NRC7, EC602288, JS97-52, EC538828, Bragg, PK472 and Hardee. Major group further divided into two groups. Major sub group consisted 51 genotypes, however minor sub group had two genotypes,
namely JS 20-90 and PS 1611. Major sub group further divided into two groups. Major group consisted 41 genotypes, however minor group had 10 genotypes including SL688, SL525, JS2063*JS95-60, PK885, AMS-MB 5-18, SL983, C-2797, Gaurav, HIMSO-1685 and Shivalika. Major group consisted 41 genotypes
viz., RVS2011-77, RVS2011-73, BAUS102, RVS2011-21, SL1074, JSM240*SL517, SL96, SP-37, JS335, CAT87, AUKS-174, RVS2011-75, JS20-78, RVS2011-32, NEC 37, RVS2011-04, NRC136, PS1225, AMS100-39, AMS243, AMS475, JS93-05, RVS2001-04, RVS28, Young, JS21-17, RVS2011-76, RVS2011-10, DS3105, JS2009* PS1475, RVS2012-15, SL958, EC46728, RVS 2012-01, SL 995, RSC 1052, RVS 2011-35, SL 953, DS 3106, RVS 2011-74 and JS20-53*JS 20-34.
Biochemical analysis based hierarchical cluster analysis
Bestowing to the hierarchical cluster investigation and the gratified values (Table 2), the active countenance outline was governed and is displayed in Fig 1. Multivariate examination owing to diversity was executed through the UPGMA. The average worth of biochemical parameters the dendrogram was discriminated into two major clusters
i.e., I and II. Cluster I and II divided into subclusters. These clusters further subdivided into minor clusters. Genotypes JS-20-78, AMS-100-99, PK-472 and Hardee fallen in a seprate group.
Biochemical parameters based principal component analysis (PCA)
Principal component analysis was conducted by taking biochemical variables concurrently. The PCA correlation illustrated that which variety possessed higher and lower content occupying unique position towards the graph (Fig 2). In these four variables, total sugar content had highest variability (58.8%).
Antioxidant enzymes activities
Antioxidative enzymes perform a key part in defending plants from the damaging consequences of drought stress. Plants change enzymatic devices encompassed in the enzymatic rummaging of Reactive Oxygen Species (ROS) for instance APX, CAT, GR and PDX. Lessons on soybean disclosed that stress tolerant plants are usually bestowed with competent antioxidant protection arrangement
(Vasconcelos et al., 2009). Earlier it was also noticed that CAT and GR had a higher ROS hunting action than APX, so, it could be assumed that CAT and GR are the most significant ROS foraging enzymes in soybean owing to their involvement in tolerance machinery. This may be entire capacity of a particular genotype to combat against these stresses.
Among antioxidant enzymes, Ascorbate peroxidase delivers protection machinery in plants to convalesce from drought. APX in unit/mg protein/min varied between 0.22 to 2.08 with maximum in genotype SL-96 (2.08) and minimum in EC-602288 (0.22). Genotypes having enhanced APX bustle may be drought tolerant probably because of advent of protuberant H
2O
2 detoxification with anticipation of H
2O
2-mediated cell injury. Elevated APX action in soybean under drought stress has been previously documented
(Kachare et al., 2019). In this experiment, CAT action in unit/mg protein/min varied in range of 0.31-1.21. CAT activities increased in the genotypes
viz., RVS2011-73 tracked by SL 96. GR commotion in unit/mg protein/min varied in range of 0.21-0.91 with maximum in genotype NRC7. However, the minimum was observed in genotypes SL 95.
Kachare et al., (2019) also observed a significant elevation in GR activity in some soybean genotypes. Guaiacol peroxidase activity in unit/mg protein/min ranged between 0.22-2. During the current study, up surged PDX motion was recorded in genotypes
i.e., SL 96, AMS100-39, RVS 2012-01 and NRC7. Similar to the present research,
Kachare (2017) and
Mishra et al., (2021c) noticed directly proportional relation between PDX activity and level of water stress in soybean.
Cluster analysis of pooled antioxidative enzymes data
In antioxidant enzymes data based dendrogram the genotypes were divided into two clusters
i.e., major cluster and minor cluster. The major cluster contained 58 genotypes while the minor cluster had only 2 genotypes
viz., RVS 2012-01 and SL 96. Major group further subdivided into two groups major sub group 1 and minor sub group 2. Major sub group 1 consisted 51 genotypes, however minor sub group had only 2 genotypes, namely NRC-7 and AMS 100-39. Minor sub group further subdivided into two parts. RVS-2011-73 genotypes came in outgroup of the cluster.
Antioxidant activities estimate based hierarchical cluster analysis
Dynamic expression profile was constructed on the basis of hierarchical cluster analysis and the content values presented in Fig 3. Multivariate analysis owing to diversity was executed using the UPGMA. The mean value of antioxidant enzymes activities of different genotypes depicting in each cluster was presented in the generated dendrogram and distinguished into two major clusters (I and II). Cluster I and II divided into subclusters. These clusters further subdivided into minor clusters (Fig 4 and Fig 5). Cluster I consisted NRC-136 and AMS100-39 genotypes as an outer group and cluster II also consisted two genotypes
viz., RVS 2012-01 and SL-96 as an outgroup.
Antioxidant activities based principal component analysis (PCA)
Principal component analysis (PCA) was drawn by considering biochemical variables instantaneously. The decoration of variations exemplified by the PCA designated by correlation coefficients explained for pair-wise connotation of the traits. The PCA correlation illustrated that genotype possessed higher and lower antioxidative content occupying unique position towards the graph (Fig 6). In these four variables, Glutathione reductase content had highest variability (64.7%).