[Relationship between leaf anatomical structure and heat resistance of 15 Rhododendron cultivars].

In this study, 17 anatomical structure indexes of 15 Rhododendron cultivars were mea-sured by scanning electron microscope (SEM). Leaf anatomical structure indexes were screened via coefficient of variation, analysis of correlation and hierarchical cluster analysis, and comprehensive evaluation on heat resistance for each cultivar was conducted by the subordinate function. The results showed that the leaves of Rhododendron cultivars were typical bifacial leaf and the epidermal anticlinal walls showed slightly sinuate. The stomata only distributed in the lower epidermis and the shape was ruleless. The anatomical structure indexes all reached a significant level difference among 15 cultivars (P<0.01), except for lower epidermis thickness (P<0.05). Thickness of lamina corneum, stomatal density, stomatal width, the thickness palisade tissue and looseness of leaf spongy tissue were the main factors related to the hardness, while other indexes, such as stomatal length, stoma aperture, stomatal opening, length and thickness of upper epidermis, length and thickness of lower epidermis, thickness of spongy tissue, the ratio of the palisade tissue to spongy tissue, tightness of leaf palisade tissue, leaf thickness and media thickness didn't show much effect on heat resistance. There were some differences among 15 cultivars in heat resistance, and the order was Rhododendron 'Song Jiang Da Tao Hong' > Rhododendron 'Zhuang Yuan Hong' > Rhododendron 'Lv Se Guang Hui' > Rhododendron 'Fen Zhen Zhu' > Rhododendron 'Wai Guo Hong' > Rhododendron 'Lan Yin' > Rhododendron 'Bi Zhi' >Rhododendron 'Da He Zhi Chun' > Rhododendron 'Guo Qi Hong' > Rhododendron 'Yu Ling Long' > Rhododendron 'Hong Shan Hu' > Rhododendron 'Ning Bo Hong' > Rhododendron 'Tao Ban Zhu Sha' > Rhododendron 'Ai Ding Bao' > Rhododendron 'Liu Qiu Hong'. According to the heat hardiness, the cultivars could be divided into 4 groups: R. 'Song Jiang Da Tao Hong', R. 'Zhuang Yuan Hong' and R. 'Lv Se Guang Hui' with high heat resistance, R. 'Fen Zhen Zhu', R. 'Wai Guo Hong', R. 'Lan Yin', R. 'Bi Zhi', R. 'Da He Zhi Chun', R. 'Guo Qi Hong' and R. 'Yu Ling Long' with medium heat resistance, R. 'Hong Shan Hu', R. 'Ning Bo Hong', R. 'Tao Ban Zhu Sha' and R. 'Ai Ding Bao' with lower heat resistance, R. 'Liu Qiu Hong' without heat resistance. However, the accurate heat hardiness evaluation of Rhododendron still needs to consider other factors, including morphological structure, physiological and biochemical indicators and genetic factor of heat resistance, the harmfulness of Rhododendron, and the recovery state after being injured by high temperature.