Studies On Classification And Heat-resistance Characteristics Of Cultivars Resources In Genus Hosta

The study consist of two parts, the first is the cultivars classification of the hostas resources, the second is the effects of the high temperature on different cultivars.(1) with a briefly retrospect the history of taxonomy of genus Hosta , also a review is give to the advance in the current taxonomic systems and phytogeography the genus, then the current classification of the hosta cultivar is analyzed ,especially the hosta show classification adopted by the American Hosta Society(AHS). Based on the field study of over 400 cultivars , a new method and program of classification system of the major hostas in cultivation according to"Dual Classification"has been put forward by the author in the first time , though now it is just conceptive as more information is needed for the key, we think it will be more useful in horticulture and landscape practice. In this classification program , a 5-degrees of criteria for classification from the most important one to the less important one are used. We combine the morphorgical AHS classifications system's morphological characteristics with the ecology type of the cultivars and the species and form characteristics, this system consists of 4 branches (according to flower time),5 groups(according to leave size), 27origins (species or forms or hybrida), 8 leave color series and 6 sub-series , the last category is the cultivars and cultivar-group. According to the system,both evolutionary and development tendency as well as practical application and morphological characteristics of cultivars are considered, with the former of first consideration. (2) The research on the change trend of the physiological indexes in varieties of hostas with different heat-resistance under the normal and high temperature condition has indicated the rate of free water and tied water, relative electrolyte leakage increased more evidently under high temperature when they have lower heat-resistance, but the content of Proline, soluble proteins and the activities of SOD, POD and CAT increased more evidently under the same higher temperature in the varieties with higher heat-resistance. All of those physiological indexes would be considered as the system of heat-resistance select for the hostas, and at the same time, as a theory reference for the other ornamental plants.