Abstract: In order to select the most suitable cultivar for planting in the tropical area of southern China，the tolerance toward high temperature stress of six summer chrysanthemum cultivars were studied. The summer chrysanthemum cultivars introduced from Nanjing，including‘Fengyunli’，‘Zaohuang’，‘Sijiju’，‘Aoyunjinkui’（referred to as‘Aojin’），‘Aoyuncaidie’（referred to as‘Aocai’），‘Aoyunhongxing’（referred to as‘Aohong’），and the Guangdong local chrysanthemum were used to be treated under high temperature stress at seedling and flowering stages，respectively. The results showed that the seedlings of‘Aojin’had no obvious heat injury under high temperature stress. Compared with those of the Guangdong local chrysanthemum，the cells were more stable in the heat-treated seedlings of ‘Aojin’，supported by the evidence that the increased extents of malondialdehyde（MDA）content，conductivity and chlorophyll degradation were smaller in‘Aojin’. Moreover，the proline content in the ‘Aojin’seedlings was significantly increased，and the survival rate of‘Aojin’seedlings was highest after recovery. In addition，the expression levels of heat shock genes CmHSP70，CmHSP90，CmHSP and CmsHSP in the‘Aojin’seedlings were increased significantly and reached the highest point after 1 h of high temperature treatment. The degrees of wilting and the physiological indexes of the‘Aojin’flowers under high temperature stress were consistent with those from the seedling treatment. According to the performance of these cultivars in both seedling and flowering stages，the heat resistance of‘Fengyunli’was inferior to‘Aojin’，while the heat resistance of‘Zaohuang’or‘Sijiju’was similar to that of Guangdong local chrysanthemum，which was inferior to‘Fengyunli’，and the heat resistance of‘Aohong’and‘Aocai’was worst. Collectively，our study indicated that‘Aojin’is the best heat-resistant cultivar and is suitable for planting in the tropical area of southern China.

Key words: summer-flowering chrysanthemum, high temperature stress, heat resistance, physiological index