Effects of drought and salt stress on seed germination characteristics of 14 Medicago sativa varieties

The tolerance of 14 Medicago sativa varieties to drought and salt stress during seed germination was compared and analysed. This provided the experimental basis for the rational selection of seed varieties with strong drought and salt tolerance in production and cultivation. Alfalfa seeds were treated with 0, 150, 200, 250, and 300 mmol·L^–1 NaCl solution and 0, 15%, 20%, 25%, and 30% PEG 6000 solution, respectively. According to the dynamic change of germination rate under different screening methods suitable to assess drought and salt stress concentration, the condition of drought and salt stress on the seed germination of different varieties of alfalfa using the standard test and the fuzzy mathematics method of subordinate function of alfalfa provided a comprehensive analysis of drought and salt resistance. The results showed that: 1) the appropriate concentrations of salt and drought stress in alfalfa were 250 mmol·L^–1 NaCl and 25% PEG-6000, respectively. 2) Under drought and salt stress, the relative germination potential, relative germination rate, and relative germination index of alfalfa seeds were significantly reduced, and the change trend of the three indexes was roughly the same, with significant differences among the different varieties (P < 0.05). The response mechanism of the relative root length of the seedlings to the two kinds of stresses was different. The root length of the seedlings was significantly inhibited under salt stress, whereas drought stress had a certain promoting effect on the root length of the seedlings, with significant differences among different varieties. Under the stress of salt and drought, the relative fresh weight was significantly reduced, with the relative dry weight less inhibited than the relative fresh weight. Under drought stress, the relative dry weight of all the varieties, except ‘Magna4030’, was greater than 1, and the difference among different varieties was significant. 3) The drought resistance of alfalfa during germination was as follows: ‘Magna995’ > ‘Sibemol’ > ‘Fado’ > ‘Magna601’ > ‘Magna551’ > ‘Salsa’ > ‘Magnum VII’ > ‘Mezzo’ > ‘Magna401’ > ‘Instinct’ > ‘Weston’ > ‘Vision’ > ‘Liangmu No.1’ > ‘Magna4030’. The salt tolerance was: ‘Fado’ > ‘Liangmu No.1’ > ‘Magna551’ > ‘Magna995’ > ‘Instinct’ > ‘Weston’ > ‘Sibemol’ > ‘Magna601’ > ‘Magna4030’ > ‘Vision’ > ‘Magna401’ > ‘Mezzo’ > ‘Magnum VII’ > ‘Salsa’. Among these, the seeds of ‘Fado’, ‘Magna995’, and ‘Magna551’ have strong drought resistance and salt tolerance and the potential for popularisation and application in arid and saline areas.