Comprehensive evaluation and construction of drought resistance index system in Hydrangea macrophylla.

With the continuous drought stress treatment to five Hydrangea macrophylla varieties of different abilities of drought resistance, twenty-five physiological-biochemical indices were mea-sured. We evaluated the drought resistance of different varieties and established the mathematic model. The results showed that leaf mass per area, cell membrane permeability (CMP), the content of malonaldehyde (MDA), the activity of superoxide dismutase (SOD), soluble sugar content, proline content, intercellular carbon dioxide and non-photochemical quenching coefficient were significantly increased under drought stress for twenty days. In contrast, relative water content, net photosynthetic rate, stomatal conductance, transpiration rate, actual photochemical efficiency of PS2 and electron transport rate (ETR) were significantly decreased. The principal component analysis classified those indices into three independent comprehensive indices (accumulative contribution of 87.1%). The principal component 1 mainly reflected the information of photosynthetic and fluorescence. The principal component 2 mainly reflected the information of plant vigor. The principal component 3 mainly reflected the information of membrane system and osmotic adjust system. Five H. macrophylla varieties were divided into three categories by clustering analysis: drought-tolerant type (including H. macrophylla 'Lavblaa') and H. macrophylla 'Taube'), intermediate type (H. macrophylla 'You and me romance'), and drought-intolerant type (including H. macrophylla cv. Endless summer bride and H. macrophylla 'Tricolor'). Comprehensive evaluation of drought resis-tance (D value) showed that the ability of drought resistance decreased in order of H. macrophylla 'Lavblaa' > H. macrophylla 'Taube'> H. macrophylla 'You and me romance'> H. macrophylla cv. Endless summer bride > H. macrophylla 'Tricolor'. Four influential indices for drought resis-tance including CMP, the activity of peroxidase (POD), soluble protein contents (SP) and ETR was screened by stepwise regression analysis, which could be used for the rapid identification of drought resistance of H. macrophylla.