Germination responses of different alfalfa cultivars to temperature and simulated drought:An analysis based on thermal time and hydrotime models
Thermal time model is used to examine the germination response of seeds at temperatures below and above the optimal one,while hydrotime model is used to fit the relationships between germination rate and water po-tential.We examined the germination responses of six alfalfa cultivars from the northern China(viz.Aohan,Dong-mu 1,Gannong 3,Gongnong 1,Longmu 803 and Caoyuan 3)to temperature and simulated drought.Polyethylene glycol(PEG 6000)was used to simulate drought conditions.Germination tests were carried out at eight tempera-tures(5,10,15,20,25,30,35,and 40 ℃)and six water potentials(0,-0.2,-0.4,-0.6,-0.8,and-1.0 MPa).Results showed that different alfalfa cultivars responded differently to temperature and drought.The base ger-mination temperatures(Tb)for the six cultivars were between-2.3 and 6.2 ℃,with Caoyuan 3 the lowest and Longmu 803 the highest.Germination rate of all the cultivars was the highest at 20 or 35 ℃.40 ℃ high temperature significantly inhibited germination of all alfalfa cultivars.The base water potentials(Ψb)of germination for the six cultivars were between-0.91 and-0.68 MPa,with Aohan the lowest and Gannong 3 the highest.Low water poten-tials-0.8 and-1.0 MPa greatly inhibited germination of all alfalfa cultivars.From the perspective of seed germina-tion response,Caoyuan 3 and Gongnong 1 are more cold tolerant,while Aohan and Longmu 803 are more drought tolerant than other cultivars.These results provide important information for alfalfa cultivation and breeding.
germination ratepolyethylene glycol(PEG)thermal time modelwater hydrotime modelMedicago sativacold tolerancedrought tolerance
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