5Dexter S T,Tottingham W E,Graber L F. I Investigations of the hardi- ness of plants by measurement of electrical conduetivity[J]. Plant Physiol, 1932,7 (1) : 63-78.
6Li R,Qu R,Bruneau A H,et al. Selection for freezing tolerance in St. Augustinegrass through somacl.onal variation and germplasm evaluation[J]. Plant Breeding, 2010,129 : 417-421.
7NiinoT, SakaiA. Cryopreservation of alginate-coated in vitro-grownshoot tips of apple, pear and mulberryl-J]. Plant Sci, 1992,87:119-206.
8Reed B M. Survival of in vitro-grown apical meri-stems of Pyrus following eryopreservation[J]. Hort Seience,1990,25:111-113.
9Scottez C,Chevreau E,Godard N. et al. Cryopreservation of cold- acclimated shoot tips of pear in vitro cultures after encapsulation-dehydration [J]. Cryobiology, 1992,29 : 691-700.
10J M Lyons.Chilling Injury in Plants[J]Annual Review of Plant Physiology,1973.