Physiological effects of high temperature stress on seedlings of two Camellia oleifera cultivars and heat tolerance evaluation

To screen out Camellia oleifera cultivars with strong heat tolerance and provide a theoretical basis for breeding new heat-tolerant varieties.

A pot experiment was conducted using the method of high-temperature stress in an intelligent greenhouse on seedlings of two C. oleifera cultivars, ‘Dabieshan 1’ and ‘Changlin 53’. Nine time gradients were set: 0 (CK), 4, 7, 14, 21, 28, 35, 42 and 49 d. Ten physiological and biochemical indicators were measured, including relative water content, relative electrical conductivity, malondialdehyde content, hydrogen peroxide content, superoxide dismutase activity, peroxidase activity, catalase activity, soluble sugar content, soluble protein content, and free proline content. The heat tolerance of the two C. oleifera cultivars was comprehensively evaluated using the average membership function value of each physiological indicator.

1) The leaf relative water content of both cultivars decreased continuously with the extension of high-temperature treatment, and the decline accelerated after 7 days of stress. After 49 days of high-temperature treatment, the leaf relative water content of both cultivars reached its minimum, with ‘Dabieshan 1’ at 71.40% and ‘Changlin 53’ at 63.32%. The relative electrical conductivity, malondialdehyde content, and hydrogen peroxide content increased continuously with the extension of high-temperature treatment and reached their maximum at the 49th day; 2) The activities of superoxide dismutase and peroxidase in the leaves of both cultivars first increased and then decreased. The catalase activity in ‘Dabieshan 1’ leaves showed a continuous upward trend, while that in ‘Changlin 53’ increased in the early stage of stress and began to decrease after 42 d of stress; 3) The proline, soluble sugar, and soluble protein contents in ‘Dabieshan 1’ leaves continued to increase. In ‘Changlin 53’ leaves, proline and soluble protein contents continued to increase in the early stage of stress, reached their maximum at the 42th day, and then decreased; soluble sugar content continued to increase in the early stage of stress, reached its maximum at the 35th day, and then began to decrease; 4) The average membership function value of ‘Dabieshan 1’ was 0.559, and that of ‘Changlin 53’ was 0.449, indicating that the heat tolerance of ‘Dabieshan 1’ was superior to that of ‘Changlin 53’.

Under high-temperature stress, the physiological response patterns of the two C. oleifera cultivars seedlings were different. The comprehensive membership function evaluation showed that the average membership function value of ‘Dabieshan 1’ (0.559) was higher than that of ‘Changlin 53’ (0.449). The heat tolerance of ‘Dabieshan 1’ was superior to that of ‘Changlin 53’.