| Seeds of Medicago sativa L. Longdong were used as test material to study the effect of ultra-drying on seed vigor and seedling growth. Silica gel was used to reduce the moisture content of seeds to 7.09%, 6.93%, 6.36%, 5.72%, 5.46%, 5.18%, 4.97% and 4.59%, respectively, from the initial moisture content of 9.03% at room temperature. After a period of hermetic storage, seed vigor was tested, and simultaneously, standard germination experiments were conducted using un-ultradried alfalfa seeds to select the optimum saline and alkaline stress concentrations for the continuation of the subsequent pot culture.All ultra-dried seeds were pot cultured in neutral environment, 15mmol L-1 alkalinity and 40mmol L-1 salinity, respectively, with un-ultradried alfalfa seeds as control, and then were determined the morphological and physiological indices of the obtained seedlings, the main results were as follows:1: Seeds with moisture contents between 5.46% and 6.36% performed better than CK, and 5.72% treatment was the best. The germination rate, germination potential and vigor index of which were all better than CK after 15d germination (for both root temperature stored and aged seeds);2: Seeds with moisture content at 5.72% performed best among all the treatments. The soluble sugar contents and APX activity of which were 22.85% and 39%, 76.21% and 115.27% times higher than the CK, respectively, while MDA contents and relative reduction of TTC were only 50.15% and 52.32%, 95% and 93.05% than that of CK (for seeds stored at room temperature and aged seeds, respectively);3: Seedlings derived from seeds with moisture contents ranged from 5.72% to 5.18% performed better than CK. On the 22nd day of germination, shoot height and leaf area of seedlings grown in neutral environment were found 2.21%～18.38% and 4.83%～14.64% times higher than CK. Shoot height, leaf number and leaf area for seedlings grown under saline stress were found 47.46%～59.32%, 37.5%～41.25% and 23.8%～65.65% times higher than CK; and the indices for seedlings grown under alkaline stress were found 15.3%～47.33%, 37.5%～43.75% and 26.05%～67.95% times higher than the CK;4: Seedlings derived from seeds with moisture contents within 5.72% and 5.18% performed better than CK. On the 22nd day of germination, chlorophyll content and root activity for the above treatments that grown in neutral environment were found 4.61%～6.3% and 0.57%～4.98% times higher than CK; chlorophyll content, soluble sugar content and root activity for the seedlings grown under saline stress were found 21.61%～71.31%, 29.07%～92.39% and 44.18%～55.77% times higher than CK, while MDA contents was found only 60.24%～84.83% of the CK. Chlorophyll content, soluble sugar content and root activity for the seedlings grown under alkaline stress were found 60.55%～140.54%, 38.06%～135.95% and 17.99%～85.84% times higher than CK, while MDA contents were found only 46.67%～70.07% of the CK;All the above indicated that appropriate ultra-drying treatment may increase vigor of Longdong seeds and accelerate the growth as well as the alkaline and saline resistant capability of seedlings. Comprehensively, seeds with moisture content at 5.72% were the highest vigor among all the treatments, and seedlings derived from seeds with moisture content at 5.46% were the best among all the treatments. Which showed that ultra-drying treatment as a kind of seeds pretreatment is capable of accelerating the growth and increasing alkaline and saline resistant capability of seedlings when the seeds were used in the short-term storage. |
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