Indian Journal of Agricultural Research

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Indian Journal of Agricultural Research, volume 55 issue 4 (august 2021) : 440-445

Water-stress Screening in Blackgram [Vigna mungo (L.) Hepper] Genotypes using Polyethylene Glycol 6000 at Seedling Growth Stage

V. A. Mohanlal1,*, K. Saravanan1, T. Sabesan1
1Department of Genetics and Plant Breeding, Faculty of Agriculture, Annamalai University, Annamalai Nagar-608 002, Tamil Nadu, India.
Cite article:- Mohanlal A. V., Saravanan K., Sabesan T. (2021). Water-stress Screening in Blackgram [Vigna mungo (L.) Hepper] Genotypes using Polyethylene Glycol 6000 at Seedling Growth Stage . Indian Journal of Agricultural Research. 55(4): 440-445. doi: 10.18805/IJARe.A-5524.
Background: Blackgram is one of the important pulse crops belongs to the Papilionaceae family. Seed germination and seedling growth are a very important step in the survival of a plant. Water stress is one of the important factors affects seedling growth.

Methods: An experiment was conducted to study the effect of water stress on seedling growth in twenty-one blackgram [Vigna mungo (L.) Hepper] genotypes at the pot culture yard of Annamalai University during March 2018. The water stress was created by using Polyethylene Glycol (6000 MW) in different concentrations (0%, 10% and 20%). Different phenotypic characters were recorded such as shoot length, root length, shoot fresh weight, root fresh weight, shoot dry weight and root dry weight at two different levels of treatment and control. The experiment was laid in a completely randomized design with two replications. 

Result: The combined analysis of variance revealed significant differences (p<0.001) among genotypes, treatments and genotypes × treatments interaction. The highest stress tolerance index (STI) was recorded by the genotype ADT-5. Based on clustering and ranking, the genotypes ADT-5, KGB-28, RU-16-9, VBG-10010 and VBG-12062 were classified as drought-tolerant. Overall, pot culture screening of 21 blackgram genotypes for drought tolerance at seedling stage using various concentrations of PEG 6000 resulted in the identification of drought-tolerant genotypes, where ADT-5 showed the highest tolerance followed by KGB-28 and RU-16-9.
Blackgram is one of the highly valuable pulse crops which is cultivated almost all part of India. Generally, pulses are rich in lysine, tryptophan and threonine which is lacking in cereals. Blackgram is rich in protein (24 gm/100 g), phosphoric acid (385 mg/100 g), vitamin b and calcium (154 mg/100g). The plant has different growth stages like sprouting, seedling, vegetative, flowering and fruiting. Among the stages, seed germination, seedling emergence and seed establishment are the key process in the survival and growth of any plant species (Almansouri et al., 2001; Delachiave and De Pinho, 2003; Hadas, 2004). Blackgram is a dicotyledon crop which has the tolerance to water stress to some extent because normally blackgram grows under rainfed conditions. However, under rainfed conditions, water stress directly affects seed germination and seedling growth of a plant (Bewley and Black, 1994; Larson and Kiemnec, 1997). So, it is essential to evaluate blackgram genotypes against water stress at germination and seedling growth stages for early-stage persistence.
Accordingly, to screen the blackgram genotypes, the molecular weight of polyethylene glycol 6000 is found to be convenient solute to create osmotic stress without causing any toxicity to plant cells (Verslues et al., 2006). Molecules of PEG 6000 are too small to influence the osmotic potential but large enough not to be absorbed by a plant (Carpita et al., 1979). Thus, PEG 6000 solution can be used in the laboratory for the screening of drought tolerance germplasm.
The experiment was conducted at the pot culture yard of Annamalai University during March 2018. The twenty-one genotypes were used for this study (Table 1). The pot culture screening for drought tolerance was carried out using Polyethylene Glycol (PEG 6000 MW). Drought stress was stimulated by irrigating PEG 6000 with water at two different concentrations namely, 10 per cent and 20 per cent by dissolving 10 and 20 grams of PEG 6000 respectively in 100 ml of water following the method of Hadas (1976). Control was maintained using irrigating normal water. The osmotic pressure exerted by these concentrations were estimated using Michel’s formulae and the estimates were 0 bar, -3 bars and -6 bars respectively at 32oC.
Ψs = - (1.18 × 10–2) C - (1.18 × 10–4) C2 + (2.67 × 10–4) CT + (8.39 × 10–7) C2T
Ψs = Osmotic potential (bar), C = Concentration (g L–1 PEG-6000 in water), T = Temperature (oC).

Table 1: List of genotypes selected for the present study.

The treatment was imposed at 7 DAS (Days After Sowing). At 17 DAS (Days after Sowing) data were recorded on shoot length, root length, shoot fresh weight, root fresh weight, shoot dry weight and root dry weight at two different levels of treatment and control. The experiment was laid in a completely randomized design with two replications. Stress tolerance index was calculated for twenty-one blackgram genotypes by using a formula recommended by Fernandez (1992). The statistical software STAR (Statistical Tool for Agricultural Research) and TNAUSTAT were used for this study.
Analysis of variance
The combined analysis of variance was worked out that showed significant differences (p<0.001) among genotypes and treatments of PEG 6000 (Table 2). Genotype × treatment interaction was also significant (p<0.001) for all the characters studied. This shows that there was a significant variation present in genotypes, treatments and genotypes × treatments. Hence, assessment of the effect of PEG 6000 solution on genotypes for drought screening was possible.

Table 2: Mean square from combined analysis of variance of blackgram genotypes for various characters under normal and water stressed condition.

Per se performance
By and large water stress affects the overall cell activities of a plant that ultimately results in a reduction in growth which premise reported earlier. The cellular elongation process and the carbohydrates wall synthesis are very susceptible to water deficit (Wenkert et al., 1978) and decrease in growth was the consequence of the turgescence laying down of these cells (Shalhevet et al., 1995). The general mean of twenty-one genotypes for shoot length was 19.07 cm in control (Table 3). It was decreased to 12.20 cm and 11.17 cm in T1 and T2 respectively (Table 4 and 5). In T2, the genotypes RU-16-9 (14.40 cm), RU-16-13 (13.80 cm) and ADT-5 (13.55 cm) recorded significant high values for shoot length (Table 5). Shoot length is reduced when the water stress is increased. The scarcity in the amount of water in drought condition results in dropping of cell growth and enlargement. According to Kramer (1974), the first determined effect due to water deficit was the growth reduction caused by the decline in cellular expansion. Results were in agreement with the findings of Babu and Rosaiah (2017) in blackgram and Deshmukh et al., (2001) in sorghum.

Table 3: Mean performance of 21 blackgram genotypes seedling in control.


Table 4: Mean performance of 21 blackgram genotypes seedling in treatment 1 (10% PEG).


Table 5: Mean performance of 21 blackgram genotypes seedling in treatment 2 (20% PEG).

A slight increase was observed in general mean of root length in T1 (11.87 cm) and T2 (12.64 cm) when they were compared to control (9.37 cm). As the plant was subjected to a water stress condition, the plant developed a good root system to uptake more amount of water from the soil. For developing a better root system, the plant diverts all the food sources from the photosynthesis process to root cells for its growth and development. This ensures the plant to uptake enough water from the soil in water stress condition. For root length, the genotypes ADT-5 (18.45 cm) and KGB-28 (18.25 cm) expressed significant high value in T2. These genotypes can be selected for root length character for breeding purposes to drought tolerance.
A gradual decrease was observed in fresh weight and dry weight of the shoot and root. Fresh root weight decreases reported in wheat cultivars (Rauf et al., 2007 and Khan et al., 2013). and sorghum (Bibi et al., 2012). Water stress condition affects the overall production of biomass. It limits the growth of the plant. In T2, the genotypes ADT-5 and KGB-28 resulted in significant high value for shoot dry weight (0.0949 g and 0.0879 g) and root dry weight (0.0421 g and 0.0525 g). Reduction in root dry weight stated by Pratap and Sharma (2010) in blackgram, Anaytullah (2007) in rice and Dezfuli et al., (2008) in maize.
In addition, root shoot ratio is a good indicator for drought screening. When a genotype expresses high root to shoot ratio, it indicates the genotype have good drought escape mechanism. High root shoot ratio was recorded by the genotypes VBN(Bg)-7 (1.54) followed by VBG-10010 (1.51) and KGB-28 (1.47). These genotypes can be selected for the root shoot ratio in drought breeding programs. Because these genotypes have good drought escape mechanism by developing a much better root system than shoot system in water-stressed condition. 
Stress tolerance index
Based on total dry weight, the stress tolerance index revealed that the genotype ADT-5 logged the highest value 2.16 followed by KGB-28 (1.92) and RU-16-9 (1.58) (Table 6). Thus, these genotypes had better tolerance than other genotypes in water-stressed condition.

Table 6: Stress tolerance index of 21 blackgram genotypes in treatment 2.

Clustering and ranking of genotypes
By using multivariate analysis, the blackgram genotypes grouped into different clusters based on the quantitative characters observed in T2 (Table 7). The cluster I was comprised of genotypes ADT-5, KGB-28, RU-16-9, VBG-10010 and VBG-12062 (Fig 1). These genotypes were identified as drought-tolerant genotypes based on their mean performance. Cluster II was classified as moderately susceptible which contained the genotypes VBG-11011, MDU Local, VBG-12005, KU-11680, VBG-13017, VBN(Bg)-6, IC-343962 and VBN(Bg)-7.

Table 7: Ranking of blackgram genotypes for drought-tolerance.


Fig 1: clustering of twenty-one blackgram genotypes for different characters in T2.

Cluster III had genotypes such as, ABG-11013, TBG-104, RU-16-13 and RU-16-14 which were moderately tolerant to drought. The genotypes IC-343943, IC-343947, T-9 and VBN (Bg)-4 were clustered in cluster IV which was the group of drought susceptible genotypes.
Using PEG 6000 appears to be useful for screening of blackgram germplasm for seedling drought tolerance. Blackgram genotypes were separated very well for their tolerance to water stress imposed by PEG 6000.
Based on the mean performance, stress tolerance index, clustering and ranking of twenty-one blackgram genotypes in pot culture screening for drought tolerance at seedling stage using various concentrations of PEG 6000 resulted in the identification of genotype ADT-5 as drought tolerant, followed by KGB-28 and RU-16-9. So, these genotypes can be used as genetic resources for drought tolerance breeding programs in future.

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