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Carbohydrate Reserve and Aerenchyma Formation Enhance Submergence Tolerance in Rice

MHR Pramanik
Department of Crop Botany, Bangladesh Agricultural University, Mymensingh 2202

IJ Shalley
Department of Crop Botany, Bangladesh Agricultural University, Mymensingh 2202

D Adhikary
Department of Crop Botany, Bangladesh Agricultural University, Mymensingh 2202

MO Islam
Department of Crop Botany, Bangladesh Agricultural University, Mymensingh 2202

Abstract/ Executive Summary:

An attempt was made to evaluate the submergence tolerance in rice using four Aman rice varieties viz. FR13A (local flood resistant, check), BRRI dhan 51 (HYV flood tolerant, check), BR 5 (HYV, susceptible) and a local aromatic rice,Ukunimadhu (local susceptible). Twenty days old seedlings of the rice varieties raised in earthen pots were submerged under 90 cm water depth in a submergence tank for 12 days and data were recorded on plant height, tiller number, carbohydrate reserve and internal anatomical structure of roots of the submerged and control (ambient) plants. Under submergence treatment Ukunimadhu showed rapid stem elongation with taller plants than the HYVs which showed shorter plant height. Tillering pattern was almost similar both in submergence treated and control plants in all the varieties. Variation in carbohydrate reserve was negligible among the varieties at ambient condition but the submergence treatment brought significant variation in carbohydrate content in them. Submergence treated FR13A and BRRI dhan 51 had the highest sugar and starch conservation ability while BR 5 and Ukunimadhu had the lowest. The higher reserved carbohydrate in the tolerant varieties might assist them to regenerate their normal growth rapidly after desubmergence. The cellular morphology of root tissue showed that intensity of aerenchyma development in submergence treated FR13A and BRRI dhan 51 was more pronounced compared to the local aromatic rice Ukunimadhu and perhaps this cellular large aerenchymatous development might be associated with the submergence tolerance of FR13A and BRRI dhan 51 than the local variety, Ukunimadhu.

Keywords: Submergence tolerance, Rice, Carbohydrate reserve, Root arenchyma

Location: Plant Ecology Laboratory of the Department of Crop Botany, Bangladesh Agricultural University, Mymensingh

Start Date:

End Date:

Program Area: Variety and Species

Commodity: Rice

Objectives:

To different rice genotypes responded morphologically as well as metabolically under fortnight submergence stress.

Methodology:

The experiment was conducted at the grill-house and Plant Ecology Laboratory of the Department of Crop Botany, Bangladesh Agricultural University, Mymensingh, during Aman season. The seeds of some selected varieties were collected from the Bangladesh Rice Research Institute (BRRI), Gazipur and some flood prone areas of Bangladesh. The treatments of the experiment consisted of four Aman rice varieties grown with submergence and ambient (control) condition. The varieties were a) flood resistant, FR13A, b) HYV BRRI dhan 51 (introgressed with SUB1 gene, flood tolerant), c) flood susceptible BR5 and d) Ukunimadhu (aromatic rice). Thus, there were altogether eight treatments. The experiment was laid out in a Randomized Complete Block Design (RCBD) with three replications. Seedlings were raised in earthen pots filled with field soil, cow dung and fertilizers. Pots were regularly watered to keep the soil moistened. Each pot contained 8 seedlings and finally three hills per pot were maintained. 20 days old seedlings were used for submergence treatment. Three pots of each variety were kept complete submerged condition in a concrete submergence tank maintaining water depth at 90 cm for 12 days. The rest three pots of each variety were grown in ambient condition as control. After 12 days of submergence treatment the pots were removed from the submergence tank and kept in ambient condition. Different intercultural operations like irrigation, fertilizer, weeding, insecticides application, etc. were carried out for better growth and development of the plants. Plant height and tiller number per hill for the rice genotypes grown in submerged and control conditions were recorded considering three hills from each pot. Plant height from each pot was taken at different growth stages during the growth period at 15 days interval starting from 20 days after sowing (DAS) till 95 DAS. The plant height was measured from ground level to the top of the longest leaf at vegetative phase and to the top of the panicle at reproductive phase. Tiller number hill^-1 from three hills of each pot was counted during the growth period at 15 days interval till 95 DAS. Immediately after de-submergence, roots of the submerged plants were collected and preserved in appropriate formalin and ethanol solution for future anatomical study in the laboratory. Anatomical investigation of the roots was carried out by preparing semi permanent slide. Transverse sections were made at 5 to 10 mm from root tips with a thickness of approximately 0.1 mm. The root sections were examined and imaged under Olympus high resolution compound microscope aided with digital camera and computer. Dried leaf samples collected from 35 days (ambient condition) and 5 days after de-submergence of the rice plants were ground finely by a grinding machine. After taking 1g powder sample, it was soaked in 20ml alcohol and filtered with another 20 ml alcohol. The filtrates were heated in water bath at 60^oC for 20 minutes. The extract solution was made up to a volume of 100 ml (stock solution). Four ml anthrone reagent solution was mixed with 1ml of the stock solution. After developing color, the solution was heated for 10 minutes and cooled in ice. When cooled, the absorbance was measured at 630 nm. A calibration curve was plotted taking absorbance of standard sugar solution at different concentrations. This curve was used as the standard curve for the estimation of sugar content of the sample. The regression equation obtained from the standard curve is given below- Y = 4.85x + 0.0382; Where, Y = Light absorbance at 630 nm x = Amount of glucose (mg). The amount of sugar in the extracts was obtained from the regression equation by putting the respective absorbance values of the extracts and taking into consideration the appropriate dilution factor. The glucose content of the sample using standard curve was measured and the value was multiplied by 0.9 to get the starch content.

Source of Information: Progressive Agriculture 27 (3): 256-264, 2016

Article Link (Online Journal): DOI: https://doi.org/10.3329/pa.v27i3.30805

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

From this study it may be concluded that th significant variation in morphological characteristics, carbohydrate contents as well as anatomical features among the genotypes for submergence stress. The genotypes FR13A and BRRI 51 did not exhausted their entire carbohydrate level even under the submergence stress like other genotypes and thus they are submergence tolerant; they also produced larger aerenchyma/air-cavity to cope with submergence stress. The most studied plastic response to flooding is the formation of aerenchyma in the root cortex. It is interesting to note that the varieties (FR13A and BRRI 51) produced larger air cavity/aerenchyma in root during submergence but the aerenchyma in them at ambient condition was very little or scanty. On the other hand, the local aromatic variety Ukunimadhu produced scanty aerenchyma at ambient condition, even under the same level of submergence stress. Aerenchyma development in other organs like stem and leaf including root at different levels of submergence stress might be more useful for valid conclusion. Finally, this study needs further experimentation in different condition like turbid water, high temperature, oxygen deficiency, longer submergence stress, etc. for exploiting their genotypic potential for submergence tolerance.

Knowledge Management: Journal