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Hydrangea macrophylla is an important ornamental plant which is popular for its large flowers, bright flowers colours, range of species and long flowering period. Hydrangea macrophylla is also a kind of eminent flowering shrub for garden landscaping and interior decoration, it has a higher market economic return. However, the drought resistance of Hydrangea macrophylla is so weak,which made it has high production and management costs. Drought not only affects the distribution and development of Hydrangea macrophylla, also affects its extensive using in landscaping. With the aim of providing simple and applied methods for the identification of Hydrangea macrophylla’s drought resistance, offering scientific and theoretical basis for the breeding for drought resistance, the experiment select four cultivars of Hydrangea macrophylla which have excellent quality and consistent growth. Using its one-year old plants from cuttings (the cultivars were numbered C, D, E, F respectively) as the test material and control the soil water content (80% PC,60% PC,40% PC,20% PC).The changes of external form, physiological and biochemical indexes under different degrees of soil drought stress were studied.The main results were shown as follows.1. The four cultivars of Hydrangea macrophylla show the different drought damage under different soil drought stress treatment. According to the drought injury index, the four cultivars of Hydrangea macrophylla’s drought resistance from the strongest to the weakest were as shown:E>F>C>D.2. Under different soil drought stress, the physiological and biochemical indexes of four cultivars Hydrangea macrophylla’s leaves were changed. With increased of the water stress, the relative water content of the leaves was decreased. The relative water content of E had the smallest change and the D had the highest decline. The E had least damage of membrane, and its soluble sugar content and praline content were higher than the other three species. SOD and POD activity of the four cultivars leaves were increased at first and then decreased, SOD and POD activity of E was higher and D had lower activity. MDA content in various cultivars shown an upward trend with increased of the soil water stress, the C, D most significant increase and the E, F increase lower. The root activity could reflect the drought resistance of different cultivars, the E maintained high root activity, and C, F second, D is the lowest at the end of water stress stage.3. The test data was treated by using principal component analysis and subordinate function analysis, and comprehensive evaluated the drought resistance of four cultivars Hydrangea macrophylla. The results showed that:the relative water content, membrane permeability, MDA content, POD activity and root activity can be used as the identification indicators for the drought resistance of Hydrangea macrophylla. The drought resistance of Hydrangea macrophylla comprehensive evaluation value (D value) to the size of:C (0.176), D (0.0152), E (0.803), F (0.354), the E has the maximum value and its drought resistance is the strongest, the worst drought resistance is D, F and C resistance center.
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