Laboratory screening of sorghum genotypes for drought tolerance using polyethylene glycol (PEG-6000)

Introduction

Sorghum (Sorghum bicolor L. Moench) is a vital cereal crop that holds a significant place in global and Indian agriculture. As one of the most resilient crops, it thrives under harsh environmental conditions, particularly in semi-arid and arid regions. Sorghum's adaptability to low water availability, high temperatures, and poor soil fertility makes it indispensable for ensuring food security in drought-prone regions. With its origins tracing back to Africa, sorghum has become a staple for over 500 million people worldwide and is a cornerstone of subsistence farming in regions facing erratic rainfall and rising temperatures. It is ranked as the fifth most cultivated cereal crop, following maize, rice, wheat, and barley. Its cultivation spans across the United States, Africa, and Asia. India, being one of the largest producers of sorghum, contributes significantly to its global production. As of 2024, India cultivated sorghum on approximately 4.7 million hectares, primarily in states like Maharashtra, Karnataka, Telangana, and Rajasthan. Despite its vast acreage, the national average productivity of sorghum remains at 950 kg/ha, which is below the global average. This highlights the need for focused research and innovations to improve yields, particularly under abiotic stresses like drought. In the country it occupied production of 4.78 million tonnes and productivity of 3428 kg ha-1. In A.P. it is cultivated in 1.20 lakh hectares with 4.10 lakh tonnes of production and productivity of 3164 kg ha-1 (Directorate of Economics and Statistics, 2024-25). Sorghum is often referred to as a "climate-smart crop" due to its remarkable ability to grow under extreme environmental conditions, including prolonged droughts and high temperatures. Drought is defined as a prolonged shortage of water available to plant, primarily due to insufficient rainfall or precipitation. It can also occur due to exceptionally high temperatures and low humidity driving the evapotranspiration in plants. Drought is one of the significant environmental factors affecting crop growth and productivity worldwide. As it can withstand drought conditions so sorghum is popularly known as "Camel crop".

Several sorghum producing regions in Africa are vulnerable to drought stress, Prasad et al. (2021) [15] . Drought stress is one of the most significant abiotic factors affecting sorghum production worldwide. It disrupts key physiological processes and reduces crop yield, particularly in rainfed agricultural systems. In sorghum, drought stress impacts growth, development, and reproduction at various stages of the crop cycle. The extent of damage depends on the timing, duration, and intensity of the drought stress. It is considered a drought-tolerant crop and can be productive under lowinput conditions, drought stress due to water deficiency affects its soil-nutrient uptake capability and nutrient mobilization and transport (Sarshad et al. 2021) [16] . PEG inhibits the seed germination by creating stress in plants. Severalphysiological characteristics have been reported as being reliable indicators for theselection of germplasm possessing drought tolerance. These characteristics includeseed germination and seedling growth in nutrient solutions with low osmotic potential(Zahoor Ahmad et al., 2015) [18] . PEG technique would be suitable for screening drought tolerance in large populations prior to yield testing trials, which could significantly reduce the overall cost and man power. Using this method maximum germplasm can be tested for drought tolerance under limited space and resources (Aradhna Kumari et al., 2014) [3] .

Materials and Methods

The experiment was conducted at the P.G Laboratory, Department of Crop physiology, at S.V agricultural College, Tirupati, using the standardized PEG protocol. Thirty sorghum genotypes obtained from the Millet Breeder, Agricultural Research Station, Perumallapalle, Chittore, Andhra Pradesh, were screened to identify resistance and susceptible genotypes. Sorghum seeds were subjected to different moisture stress condition using PEG-6000 at different Percentages (0, 5, 10) in petriplate method. Observations on germination percentage, root length, shoot length and seedling vigor index (SVI) for all the 30 genotypes were recorded. Aqueous solutions of 0,5%,10% were obtained by dissolving 0,5g and 10g of Poly ethylene glycol in 100 ml of distilled water respectively by using the formula as suggested by Michel and Kaufmann,1972. Uniform seeds of different genotypes were collected and these seeds were placed on moistened filter paper in glass petridishes. Filter papers were moistened in the beginning and at regular intervals with the above mentioned solutions. Every day number of seeds germinated were recorded. On the seventh day, the shoot and root lengths were recorded in centimeters

Design and Layout

The experiment was conducted in a completely randomized design (CRD) with 30 Sorghum genotypes. There were Three treatments (0,5%,10%) with Three replications.

Observations Recorded Germination percentage

Seed germination was recorded at every day after placing the seeds in petridishes upto seven days and it was expressed in percentage. A seed was considered as germinated, when the radicle was protruded out the seed coat. Germination percentage of seed was worked out by the following formula (ISTA, 1995).

Seedling vigour index (SVI)

Shoot length and root length of seedlings were recorded in petriplates on seventh day from the date seeds were kept for germination. Seedling vigour index was calculated by the following formula suggested by Abdul Baki and Anderson (1973) [1] and averaged.

Shoot length was measured at seventh day from the date seeds were kept for germination and expressed in cm.

Root length was measured at seventh day from the date seeds were kept for germination and expressed in cm.

Results and Discussion

The data on effect of induced moisture stress on germination percentage, seedling vigor index, shoot length and root length using petriplate method was presented here.

Germination percentage

Sorghum genotypes screened for moisture stress tolerance using Petri plate method at three different concentrations of PEG-6000 viz., control, 5% and 10% differed significantly for germination percentage. The mean GP significantly declined from 92.22% (Control) to 69.33% (10% treatment), indicating a direct inhibitory effect of the treatment on seed viability.

Control Conclusion (Optimal Conditions)

Performance: High, with a mean of 92.22%. Highest Performers: The majority of genotypes achieved a perfect 100.00% germination. Lowest Performer: NJ-2711 had the lowest initial viability at 66.67%.

5% Treatment Conclusion (Moderate Stress)

Performance: Moderate decline, with a mean of 80.89%. Highest Performers: Genotypes including NJ-2791 and NTJ 5 maintained a perfect 100.00% rate. Lowest Performer: NJ-2841 showed the highest sensitivity, with a low of 53.33%.

10% Treatment Conclusion (High Stress):

Performance: Significant decline, with a mean of 69.33%., Highest Performers (Most Tolerant): NJ-2791 and NTJ 5 were the only genotypes to maintain 100.00% germination at the highest stress level, Lowest Performers (Most Sensitive): NJ-2794 and N-15 were the most susceptible, with the lowest rate of 33.33%. Majid Khayatnezhad et al. (2010) [12] reported significant genotypic differences among the four corn cultivars at different levels of drought treatment (distilled water (0), -2, -4 and -8 bars). They also observed a significant decrease in percentage of germination and germination rate. Batool et al. (2014) [4] also stated that osmotically induced water stress adversely affect the germination and seedling growth of maize varieties. Khodarahmpour (2011) [8] observed that there was a decrease in germination% among maize hybrids due to drought stress increment and maximum germination percent was delayed. Zahoor Ahmad et al. (2015) [18] also reported that different levels of PEG-6000 suchas control, -0.2MPa, -0.4MPa, -0.6 MPa and -0.8 MPa showed significant effect on the germination of maize hybrids. Decrease in seed germination under water stress condition could be due to metabolic disorders such as slow hydrolysis of substrate compounds in endosperm or cotyledons and slower transportation of hydrolyzed material to developing embryo axis (Habtamu Ashagre et al., 2014) [10] .

Seedling Vigour Index

Seedling vigour index of Sorghum genotypes differed significantly at control, 5% and 10% PEG concentrations Seedling vigour index is a good indicator to evaluate the ability of any seed to germinate and produce normal seedlings (Perez et al. 2006) [14] . The SVI experienced a severe drop, with the mean plummeting from 1774.01 (Control) to 296.62 (10% treatment), showing a major impact on overall seedling health and growth potential.

Control Conclusion (Optimal Conditions)

Performance: High, with a mean of 1774.01, Highest Performer: NJ-2726 displayed the maximum vigour (2802.80)., Lowest Performer: NJ-2841 had the lowest vigour (857.80).

5% Treatment Conclusion (Moderate Stress)

Performance: Moderate decline, with a mean of 778.70., Highest Performer: NJ-2685 exhibited the highest vigour (1352.50), Lowest Performer: NJ-2711 was the most affected by this stress level, recording the minimum SVI (202.17).

10% Treatment Conclusion (High Stress)

Performance: Severe decline, with a mean of 296.62., Highest Performer (Most Tolerant): NJ-2791 proved the most resilient, registering the highest SVI (609.00), which is double the population mean., Lowest Performer (Most Sensitive): NJ-2794 was the most compromised genotype, showing the minimum SVI of only 73.50. Similarly significant differences among corn hybrids for seed vigour in all drought levels (0, -3, -6, -9 and 12Bar PEG6000) were observed by Khodarahmpour (2011) [8] . Das and Kalika (2010) [6] studied locally grown rice cultivars of Assam under different moisture regimes like 0 bar, -2 bars and -6 bar. They observed that moisture deficit resulted in lowering of seedling vigour and speed of germination in all cultivars although the cultivars varied significantly in their response to moisture stress. Reduction in SVI was due to reduction in both seed germination and seedling length.

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