Identification of heat-tolerance cultivars of Delphinium and their acclimation responses to high temperature stress

Delphinium is an important summer-flowering ornamental, but its sensitivity to high-temperature stress limits its ability to over-summer in open fields, thereby hindering its widespread application. There are no reports on the screening of high-temperature-tolerant Delphinium and their mechanisms of response to high-temperature stress. We collected 25 Delphinium and assessed their high-temperature tolerance. Hunky Dory and Jenny's Pearl exhibited the greatest high-temperature tolerance, being able to flower and set seeds successfully in natural high-temperature environment of Guanzhong area of Shaanxi during summer. In contrast, Benary's Pacific and Blue Bird showed the least high-temperature tolerance and failed to flower and set seeds under the same conditions. Under high-temperature stress, Hunky Dory and Jenny's Pearl had significantly lower water loss rates compared to Benary's Pacific and Blue Bird. Under high-temperature condition, Hunky Dory and Jenny's Pearl exhibit a denser leaf structure, with their cuticular wax amount increasing by 42.62 and 30.79 %, respectively, and their soluble sugar content increasing by 91.62 and 144.02 %, respectively. Moreover, the stomatal opening ratio of Hunky Dory and Jenny's Pearl remained unchanged under high-temperature stress, while that of Benary's Pacific and Blue Bird decreased by 66.86 and 35.53 %, respectively. The superoxide dismutase activity of Hunky Dory and Jenny's Pearl increased by 203.19 and 45.23 %, respectively, under high-temperature stress, enabling them to more effectively scavenge reactive oxygen species and alleviate oxidative stress. These findings highlight that stronger capabilities of water retention and efficient ROS detoxification systems underlie the greater tolerance of Hunky Dory and Jenny's Pearl to high-temperature stress.