Abstract:

The aim of this work was to investigate the effect of chitosan as a seed treatment for alfalfa （Medicago sativa） to improve seed germination and seedling growth in saline alkali conditions. Seeds of 15 alfalfa varieties were soaked in chitosan solution and their germination and growth under saline alkali conditions were monitored. First， the seeds of the 15 varieties were subjected to saline alkali stress （0， 50， 75 and 100 mmol·L^-1， NaCl∶Na₂SO₄=9∶4， pH=8.3） to determine their tolerance at the germination stage. This revealed the optimal stress concentration for further experiments， and identified the cultivars showing saline alkali tolerance at the germination stage. The 75 mmol·L^-1 treatment was identified as the optimal stress concentration， and three alfalfa germplasm lines with tolerant， moderately tolerant， and sensitive genotypes were selected for further experiments. Seeds of the sensitive， moderately tolerant， and tolerant genotypes were soaked in solutions containing chitosan at a range of concentrations （0， 25， 75， 125， 175， and 200 mg·L^-1） for 12 hours and then exposed to 75 mmol·L^-1 saline alkali stress during the seed germination stage， or distilled water as the control （CK）. The results show that， for all three alfalfa materials， the seed germination indexes such as germination energy， germination percentage， germination index， vitality index， and seeding indexes such as root length， seedling length and fresh weight were higher after the chitosan-soaking treatment than after treatment with saline alkali stress alone. Across the chitosan concentration range tested， as concentration increased， each germination index first increased and then decreased. The optimal effect was achieved when seeds were soaked in chitosan at a concentration of 75 mg·L^-1. Additionally， soaking the seeds in different concentrations of chitosan had different effects on the germination indexes of the three germplasm lines， with a significant concentration dependent effect within a certain range. In conclusion， a chitosan seed soaking treatment can effectively alleviate the inhibitory effect of saline alkali stress on the germination of alfalfa seeds and significantly improve seedling growth. The results of this study provide an effective methodology for improving the adaptability of alfalfa and enhancing its establishment in saline alkali land.

Key words: chitosan, saline-alkaline stress, alfalfa, seed germination