Germination and seedling growth of ultra-dried alfalfa seed under alkali stress

The “Longdong” alfalfa (Medicago sativa L.) was used to determine the effect of alkali stress on germination and seedling growth of ultra-dried seeds. NaHCO₃ and Na₂CO₃ were mixed in the ratio of 9∶1 for a typical alkali stress. Alkali concentration gradients of 0 mmol·L^-1, 2 mmol·L^-1, 5 mmol·L^-1, 15 mmol·L^-1 and 25 mmol·L^-1 were used in the germination test of non-ultra-dried seeds. The germination test showed 15 mmol·L^-1 was the highest alkali concentration limit for “Longdong” alfalfa with significant stress effect. Silica gel was used to reduce the moisture content of alfalfa seeds to 7.09%, 6.93%, 6.36%, 5.72%, 5.46%, 5.18% and 4.97% from an initial moisture content of 9.03% (CK). Next, a sand culture was developed to study the germination and seedling growth of different seeds under 15 mmol·L^-1 alkali stress and neutral environments. The results showed that ultra-dried seeds with moisture contents of 6.93%~5.72% had better germination and seedling performance than CK under neutral environment. The 7-day seedling survival rate, 17-day shoot height and 23-day leaf number were respectively 18.18%~22.73%, 16.79%~32.49% and 15.65%~29.41% higher than those of CK. While seedlings of the ultra-dried seeds with 6.36%~5.46% moisture content performed obviously better in alkali stress compared with CK, the 7-day survival rate and 17-day shoot height were respectively 11.30%~30.66% and 1.64%~34.64% higher than those of CK. The 23-day leaf number was approximately 79.32%~98.24% of CK. The results suggested that ultra-drying pretreatment accelerated alfalfa seed germination and seedling growth under neutral and alkali stress.