Abstract:
The comparative study of the physiological responses of two soybean cultivars, i.e.,SJ.5 and KKU.35 at seedling stage grown in nutrient solution at the salinity level of 0, 40, 80 and 120 mM NaCI was conducted. The responses were monitored by measuring photosynthetic rate, water use efficiency, chlorophyll a and b content เท the 3rcl and the 5th leaves from the top, sodium, chloride and potassium ion content in roots, stems and leaves, and growth parameter, i.e., leaf area, stem and root dry weight, root/shoot ratio (R/S), relative growth rate (RGR) and specific leaf weight (SLW) at 0, 4, 8, 12, 16 and 20 days after salt treatments. It was found that both soybean cultivars responded to salinity. Photosynthetic rate, water use efficiency, leaf chlorophyll contents, and growth parameter, i.e., leaf area, stem and root dry weight, relative growth rate significantly decreased after 16 and 20 days of salt treatment. Sodium and chloride content significantly increased in stems and leaves, while potassium ion content in stems and roots decreased. At 120 mM NaCI treatment, the sodium ion accumulation in SJ.5s leaves was found on day 12 of salt treatment, while the sodium ion accumulation was detected on day 4 in KKU.35's leaves. The slower movement of sodium ion into leaf tissues in SJ.5 supported the better salt tolerant characters of SJ.5 when compared to KKU.35. The potassium ion accumulation in both SJ.5 and KKU.35 leaves suggested the K+ role in osmotic adjustment and Na detoxicity during salt stress เท soybean. เท addition, it was found that root/shoot ratio and specific leaf weight significantly increased for 16 and 20 days after salt treatments. At 120 mM NaCI treatment, KKU.35 plants wilted and died at the end of the experiment while SJ.5 plants still survived. This study suggests that it is possible to use photosynthetic rate, water use efficiency, leaf chlorophyll contents, ion contents in plant tissue and growth analysis as parameters for salt resistant line selection. From the two soybean cultivars studied, SJ.5 should be more salt-resistant when compared to KKU.35.