Screening for water stress induced by polyethylene glycol- 6000 in green gram (Vigna radiata (L.) R. Wilczek)

Introduction

Mung bean (Vigna radiata (L.) Wilczek) commonly known as green gram is the most important pulse crop having economic and nutritional significance. It has tremendous health benefits due to presence of bioactive compounds. Short life cycle and nitrogen fixing ability of mung bean makes it compatible for major cropping system. However the production of mung bean is drastically affected by several biotic and abiotic stresses. Among the abiotic stresses, drought stress is major constrain in mung bean production. Seed germination and early seedling growth are considered as most critical phases for seed establishment, which determines successful crop production and gets reduced with the onset of drought. Occurrence of dry spell with varying magnitude affects number of physiological and metabolic process like germination, growth, photosynthesis, respiration, nutrient metabolism etc. during the crop growth period which ultimately lead to poor growth and yield [Durga et al. (2003)] [1] . Therefore it becomes necessary to develop drought tolerant genotype which could withstand limited soil moisture stress and give better yield. Selection of new variety is difficult due to the wide range of plant stress responses with overlapping functions between their components creating complex mechanisms of resistance [Kaur et al. (2017) [4] . It clearly implies that, for successful drought tolerance breeding, reliable methods for screening of desirable genotypes must be opted. The use of osmotic substances having high molecular weight such as PEG is most common and reliable method to test the drought tolerance ability of crop plants during seed germination and seedling establishment [Turkan et al. (2005) [13] & Zarei et al. (2007)] [14] . Polyethylene glycol (PEG) leads to reduced water potential causing osmotic shock without any harmful toxic effect on plants. Varieties that can germinate under reduced water potential usually germinate and establishes into seedlings. In the present investigation attempt has been made to screen twenty five mung bean genotypes at three different concentrations (-0.3 MPa, -0.6 MPa and -0.9 MPa) of PEG besides control by evaluating their germination, root length, shoot length and vigour index under laboratory conditions to identify drought tolerant genotype.

Materials and Methods

Twenty five mungbean genotypes were screened for water stress tolerance using Poly Ethylene Glycol-6000 at different concentrations (-0.3, -0.6 and -0.9 MPa) besides control (water) in CRD design with two replications at ICAR-RCAER Palandu, Ranchi. Twenty five seeds were taken from each genotype and was surface sterilized initially with 0.1% (w/v) Mercuric chloride for three minutes and then washed thoroughly with distilled water. Poly Ethylene Glycol (PEG) 6000 was used to prepare external water potentials of -0.3, -0.6 and -0.9 MPa as per method described by Swathi et al. (2017) [11] . The surface sterilized seeds were soaked in different concentrations of PEG solution as well as in distilled water (control) separately for five hours. Further the seeds were germinated on a paper towel placed in petridish which was completely wetted with water and different concentrations of PEG solutions respectively and were incubated for 10 days at room temperature. After ten days of incubation, seedlings were removed from petridishes and data was recorded for germination percentage, root length, shoot length and vigour index. The germination percentage was calculated by the formulae

number of seed germinated total number of seed kept for germination × 100

Root length was recorded in centimeters from base to tip of main root while, shoot length was recorded in centimeters from base to the tip of the leaf blade. Vigour index was calculated by the following formula.

Vigour index = (shoot length + root length) × germination percentage.

The data obtained was further subjected to ANOVA of CRD.

Results and Discussion

In the current scenario of climate change, the most important factor for crop production is water. Mung bean is an important legume cultivated throughout the country which can thrive well under drought prone condition. But the response of mung bean genotypes varies differentially under drought condition. The study of water potential enables to identify the genotype suitable for cultivation under moisture stress condition. Polyethylene glycol is the best osmoticum that induces significant water stress without causing any toxic effect. The analysis of variance for four characters was significant which clearly indicates that ample amount of variation was present for all the traits at different concentration of PEG (-0.3 MPa, -0.6 MPa and -0.9 MPa) besides control (table 1). Similar findings were observed by Mahapara et al. (2022) [5] , Imtiyaz et al. (2020) [3] , Kaur et al. (2017) [4] , Swathi et al. (2017) [11] and Dutta and Bera (2008) [2] . The mean performance of twenty five genotypes of mungbean for four different characters at different concentration of PEG -6000 is presented as follows (table 2). The rate of germination varied in control and at various concentration of PEG (-0.3 MPa, -0.6 MPa and -0.9 MPa) due to decrease in water potential gradient resulting in limited water uptake by seed leading to reduced seed germination. Germination percentage ranged from 15-100% under control, 12.5 to 97.50% at -0.3 MPa, 10% to 92.86% at -0.6 MPa and 5% to 70% at -0.9 MPa. It was observed that, the genotypes KL 4, samrat, banka local, MH 921 HUM 16 and Pusa Vishal depicted higher germination percentage under control as well as different concentration of PEG (-0.3 MPa, -0.6 MPa and -0.9 MPa). Similar findings were reported by Kaur et al. (2017) [4] , Mahapara et al. (2022) [5] , Nanditha et al. (2022) [6] , Osmani et al. (2021) [7] , Rohit et al. (2020) [10] , Rajput et al. (2022) [8] and Swathi et al. (2017) [11] . Shoot length decreased with increase in PEG concentration. Under control condition shoot length ranged from 0.62 cm to 8.01 cm with an average mean of 4.91 cm while it was 0.25 cm to 8.00 cm with an average of 3.94 cm at -0.3 MPa. At -0.6 MPa shoot length ranged from 0.40 cm to 5.57 cm with an average of 1.93 cm. while, at -0.9 MPa it was 0.14 cm to 2.27 cm with a mean of 0.85 cm. The genotype Samrat (2.27 cm), KL 4 (1.79 cm), Banka Local (1.51 cm) and Pusa Vishal (1.50 cm) recorded maximum shoot length. The studies of Kaur et al. (2017) [4] , Mahapara et al. (2022) [5] , Nanditha et al. (2022) [6] , Osmani et al. (2021) [7] , Rohit et al. (2020) [10] , Reyes et al. (2023) [9] and Swathi et al. (2017) [11] reported the same. Under reduced water potential, there was decrease in the root length, but those genotypes whose relative decrease in root length was less were considered as drought tolerant genotypes. The range of root length under control condition was 0.50 cm to 10.06 cm having mean of 5.49 cm while at -0.3 MPa it was 0.37 cm to 6.72 cm depicting average of 4.26 cm. At high water potential (-0.6 MPa), the range of root length was 0.21 cm to 4.67 cm with an average of 1.79 cm while it was 0.10 cm to 2.31 cm having mean of 0.83 cm at -0.9 MPa. The genotype Samrat (2.31 cm), KL 4 (2.28 cm), Banka Local (2.24 cm) and LGG 524 (1.69 cm) recorded maximum root length and were considered as drought tolerant genotype. Similar findings were reported by Mahapara et al. (2022) [5] , Kaur et al. (2017) [4] , Nanditha et al. (2022) [6] , Osmani et al. (2021) [7] , Rohit et al. (2020) [10] , Reyes et al. (2023) [9] and Swathi et al. (2017) [11] . Reduced water potential inhibit rate of germination as well as suppress growth of seedling hence lead to reduction in vigor index. Under control condition vigour index ranged from 21.30 to 1502.60 with an average value of 947.59. At reduced water potential (-0.3 MPa) the vigour index ranged from 9.75 to 1438.65 with a mean value of 659.22. At high water potential (-0.6 MPa), the range of vigour index was 19.35 to 825.97 with an average of 216.34. At higher concentration of PEG (-0.9 MPa), vigour index ranged from 1.35 to 284.90. The genotype KL 4 (284.90), Samrat (256.30) and IPM 409-4 (124.16) recorded maximum vigour index. The results was in accordance with the study of Mahapara et al. (2022) [5] , Kaur et al. (2017) [4] and Swathi et al. (2017) [11] .

Acknowledgement

AcknowledgementThe author is highly thankful to Palli Siksha Bhawan, Sriniketan, Viswa bharati & ICAR-RCAER Palandu for providing necessary guidelines and support to complete research work. Dr. Amitava Paul and Dr. R. S. Pan have cooperated and helped in collection of field data, Biochemical analysis, statistical analysis and preparation of manuscript.

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