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Effect of Drought Stress on Gas Exchange Characteristics of Four Soybean Genotypes

J. A. Chowdhury
Senior Scientific Officer
Agronomy Division, Bangladesh Agricultural Research Institute (BARI), Gazipur-1701.

M. A. Karim
Professor
Department of Agronomy, Bangabandhu Sheikh Mujibur Rahman Agricultural University (BSMRAU), Gazipur-1706.

Q. A. Khaliq
Professor
Department of Agronomy, Bangabandhu Sheikh Mujibur Rahman Agricultural University (BSMRAU), Gazipur-1706.

A. U. Ahmed
Principal Scientific Officer
Plant Pathology Division, BARI, Gazipur-1701, Bangladesh.

M. S. A Khan
Senior Scientific Officer
Agronomy Division, Bangladesh Agricultural Research Institute (BARI), Gazipur-1701.

Abstract/ Executive Summary:

An experiment was conducted in a venyl house at the environmental stress site of Bangabandhu Sheikh Mujibur Rahman Agricultural University, Gazipur during September to December 2012 to determine the changes of photosynthesis and some related traits under drought stress in soybean genotypes. Four studied genotypes viz. Shohag, BARI Soybean 6 and BD2331 (relatively stress tolerant) and BGM2026 (susceptible) were tested against two water regimes such as water stress and non-stress. Results indicated that gas exchange characteristics were positively correlated with plant growth. Photosynthesis and stomatal conductance showed more reduction in susceptible genotypes than the tolerant ones. Transpiration rate was found minimal in tolerant genotypes. Changes in leaf growth attributes of the four selected genotypes were compared under drought (water) stress conditions which is one of the major plant parts related to gas exchange. Generally, drought stress decreased the leaf area more in susceptible genotype than tolerant genotype. From the result, genotype BGM2026 which recorded the lowest photosynthesis, stomatal conductance, leaf area but highest transpiration rate was considered as drought susceptible whereas BARI Soybean-6, Shohag and BD2331 were more drought stress tolerant which have better mechanisms of drought tolerance.

Keywords: Soybean; Drought; Photosy on thesis; Transpiration; Stomabal conductance

Location: Bangabandhu Sheikh Mujibur Rahman Agricultural University, Salna, Gazipur.

Start Date: 00-09-2012

End Date: 00-12-2012

Program Area: Variety and Species

Commodity: Soybean

Objectives:

To determine the changes of photosynthesis and some related traits in soybean under drought stress situation.

Methodology:

A pot experiment in a vinyl house was conducted at the Bangabandhu Sheikh Mujibur Rahman Agricultural University, Salna, Gazipur during September to December 2012. Three relatively water stress tolerant (Shohag, BARI Soybean 6 and BD2331) and one susceptible (BGM 2026) genotypes, selected from the previous experiment, were used in this study to determine the changes of photosynthesis and some related traits in soybean under drought stress at vegetative and pod development stages. Seeds of tolerant genotypes and susceptible genotypes were sown in plastic pots (24 cm internal diameter and 30 cm height). The pot was filled with mixture of soil and cow dung at a ratio of 4:1. Pot contained 12.0 kg of soil which was equivalent to 9 kg oven dry soil and holds about 28% moisture at field capacity (FC). Soil used in the pot was sandy loam. Fertilizer rates of 70 mg N, 35 mg P, 180 mg K and 20 mg S pot^-1 in the form of urea, triple super phosphate, muriate of potash and gyps um was added and well mixed with the soil before pouring into the pots. Six seeds pot^-1 were sown on 3 September, 2012. After seedling establishment two uniform and healthy plants pot^-1 were allowed to grow. Two watering treatments of the plants viz. drought stress i.e. water stress (50% water of the FC) and non - stress i.e. control (80% water of FC) were applied at 21 days after emergence (DAE) and maintained throughout the growing season. The pots were arranged in a completely randomized design under Facto rial arrangement with four replications (two plants pot^-1 considered as one replication). There were four genotypes and two water regimes treatments (hereafter referred to as non - stress and water stress treatments) were included as variable treatments. Weeding and spraying were done as normal management practices for all the treatments. Some growth parameters such as leaf area, leaf weight, transpiration rate and gas exchange was measured which are described below: Leaf samples were taken to determine leaf biomass accumulation at vegetative and pod development stages. At each sampling, leaves of two plants pot^-1 were removed and leaf area plant^-1 was measured by an automatic leaf area meter. Leaves were oven dried at 70 °C to a constant weight and dry weight taken. Specific leaf area (SLA) and specific leaf mass (SLM) were also measured.

Specific leaf area (SLA) is the ratio of leaf area to leaf dry weight. It is used to understand the quantity of plant tissue employed for photosynthesis per unit of leaf tissue. It was determined by the following formula: SLA ={ Leaf area/Leaf dry weight (cm² g^-1 )}. The specific leaf mass (SLM ) indicates the leaf thickness, and it was determined by the following formula: SLM = {Leaf dry weight/ Leaf area (g cm^-2)}. The transpiration rate and leaf gas exchange was measured at the pod development stage using a portable photosynthesis system (LICOR - 6200). The data were analyzed by MSTAT - C statistical package program. The difference between the treatments means were compared by Least Significant Difference (LSD) test (Gomez and Gomez, 1984). Functional relationship between stomatal conductance and photosynthesis was established through correlation and regression analyses by using Excel program.

Source of Information: Bangladesh J. Agril. Res. 41(2): 195-205, June 2016, ISSN 0258-7122

Article Link (Online Journal): DOI: http://dx.doi.org/10.3329/bjar.v41i2.28215

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

It is clear from this study that drought stress tolerance of genotypes Shohag, BARI Soybean 6, BD2331 was associated with higher photosynthetic efficiency and stomatal conductance, maintaining higher leaf area and lower transpiration rate and genotype BGM2026 showed lower tolerance to drought stress.

Knowledge Management: Journal