Cold Hardiness Of Eleven Introduced Evergreen Ilex Cultivars

Ilex cultivars are evergreen ornamental plants, which have beautiful shape and cute fruits. Meanwhile, they are resistant to low temperature. In USA, there are hundreds of Ilex cultivars widely applied in gardens.To explore the cold hardiness of Ilex cultivars introduced from USA, we take Illex cassine’Tensaw’, Ilex’Emily Bruner’, Ilex’Mary Nell’, Ilex × attenuate ’Forsteri’, Ilex × attenuata’Savannah’, Ilex × attenuata’Bronze Beauty’, Ilex glabra’Shamrock’, Ilex crenata’Schworbel’s Compacta’, Ilex vomitoria’Anna’s Choice’, Ilex vomitoria’Oscar Gray’ and Ilex × meservea’Blue Maid’as materials.The relative conductivity, malondialdehyde content, superoxide disproportionation enzyme activity, peroxidase activity, free proline content and soluble protein content of vitro leaves of each cultivar were measured under different temperature (0 ℃,-5 ℃,-10 ℃,-15 ℃,-20 ℃ and -25 ℃) at four periods of winter in December,2014, January, February and march,2015. The semi-lethal temperatures were calculated by relative electric conductivity(Rec) and logistic equation. The membership function of indexes was applied to evaluate the cold hardiness. The results are summarized below:1. Under low temperature treatment, the relative electrical conductivity of the eleven Ilex cultivars increased with "S" curve. During the winter, the temperature was increased firstly then decreased, the REC was positively correlated with the temperature. With the treatment temperature decreased, the MDA contents increased gradually. The MDA contents of eleven Ilex cultivars dropped as the dropping of temperature, rose as the rising of temperature.2. Under chilling treatment, the SOD activities of the eleven hybrid evergreen Ilex cultivars increased firstly then decreased. During winter, the SOD activities of Ilex cultivars were negatively correlated with the temperature, only’Shamrock’ gradually decreased. With treatment temperature went lower, the changes of POD activities of Ilex cultivars were different, POD activities of’Tensaw’and’Bronze Beauty’increased firstly then decreased, the POD activities of’Emily Bruner’,’Mary Nell’.’Fosteri’,’Savannah’,’Blue Maid’and’Schworbel"s Compacta’decreased firstly, then increased, but the POD activities of’Shamrock’,’Anna’s Choice" and ’Oscar Gray’gradually increased. During wintering periods, the POD activities of eleven Ilex cultivars decreased firstly then increased, positively correlated with the temperature.3. With treatment temperature decreased, proline contents of eleven hybrid evergreen Ilex cultivars increased firstly then dropped, while proline contents of ’Shamrock’gradually increased at February. During overwintering periods, the proline contents increased as the temperature dropping, decreased as the temperature rising. With treatment temperature decreased, the soluble protein contents increased firstly then decreased. During wintering periods, the soluble protein contents increased firstly then decreased, negatively related to the temperature.4. During overwintering periods, the cold hardiness of eleven Ilex cultivars had significantly differences. LT50 values of’Savannah’,’Mary Nell’,’Anna’s Choice’ and’Blue Maid’were lowest in January. LT50 values of’Tensaw’,’Emily Bruner’ ’Fosteri’,’Bronze Beauty’,’Shamrock’,’Schworbel’s Compacta’and’Oscar Gray’ were lowest in February. This indicates that cold hardiness was complex, and can not be assessed by LT50 of a period.5. Synthetic evaluation of LT50 and the membership function indicated that the ranking of cold tolerance of the tested Ilex cultivars was:’Shamrock’> ’Forsteri’>’Emily Bruner’>’Schworbel’s Compacta’>’Anna’s Choice’>’Blue Maid’> ’Tensaw’>’Bronze Beauty’>’Oscar Gray’>’Mary Neh">’Savannah’.