Effect of seed priming on germination, morphological and physiological characteristics of sesame (Sesamum indicum L.) under alkalinity stress

Background and objectives: Alkalinity stress caused by the alkaline salts such as Na2CO3 or NaHCO3 in the soil. Alkaline stress affected germination, growth and crop productivity. Moreover, the alkalinity stress can directly damage plant growth, alter the availability of nutrients, and disrupt the balance of ions and mineral nutrition. The application of different seed pretreatment methods is one of the ways to stimulate seed germination and growth in stress condition. One of the most common methods is the use of halopriming. Halopriming or soaking of seeds in salt solutions is one of method seed priming, which enhances germination and seedling emergence under adverse environmental conditions. So, the objective of this study was to investigate the effects halopriming on growth of sesame under alkaline stress condition.
Materials and methods: In first experiment, factors were priming with NaCl with concentrations 0, 50, 100 and 150 mM for 6, 12, 18 and 24 hours. In second experiment, factors were priming with NaHCO3 with concentrations 0, 10, 20 and 30 mM for different times 6, 12, 18 and 24. Third experiment was conducted basis on result were obtained from two previous tests. In this experiment, factors were priming (non-primed (control), distilled water (hydropriming), NaCl and NaHCO3) and alkalinity stress (0, 15, 30 and 45 mM). Alkaline stress in the pots was created by adding NaHCO3, to half strength Hoagland’s solution. Control plants were only irrigated with half strength Hoagland’s solution. In this experiment, shoot and root height, potential quantum yield (Fv/Fm), performance index (PI), proline, carbohydrate, malondialdehyde content, potassium content, sodium content and sodium to potassium rate were measured.
Results: Results obtained from first experiment suggested that 50 mM NaCl for 24 hours as the best treatment. Results second experiment suggested that 30 mM of NaHCO3 for 18 hours duration as the best treatment. Results third experiment showed that alkalinity stress reduced shoot length, leaf area, potential quantum yield (Fv/Fm), performance index (PI), potassium content and potassium to sodium rate, whereas increased proline, carbohydrate content and sodium content. Priming different treatments was increased root length, shoot length, leaf area, potassium and potassium to sodium rate compared to control (non-primed). In all of alkalinity levels, priming different treatments decreased malondialdehyde content, whereas increased Fv/Fm and root length.
Conclusion: Totally, results showed that alkalinity stress decreased growth of sesame and in alkalinity stress, seed halopriming decreased membrane damage (as indicated by low MDA concentration) and improved plant growth in sesame.