Abstract:

Highly heat-tolerant Lilium Asiatic hybrids can be used as breeding materials to improve heat tolerance and ornamental properties of L. davidii var. unicolor. L. davidii var. unicolor and 23 Lilium Asiatic hybrids were subjected to long-term natural heat stress in summer, and the heat damage index for each organ of the lilies was calculated. 10 lilies with different levels of heat tolerance were subjected to short-term heat stress at 42℃ for 18 h during the budding stage, and changes in the physiological indicators of leaves and buds were measured to comprehensively evaluate their heat tolerance. Under long-term natural heat stress, the heat damage index of each organ was analyzed using membership function and cluster analysis to select nine highly heat-tolerant germplasm: ‘Easy Whisper’, ‘Trendy San Fransico’, ‘Sugar Love’, ‘Tiny Double Dutch’, ‘Trendy Havana’, ‘Heart Strings’, ‘Corsage’, ‘Landini’ and ‘Tiny Double You’; 11 moderately heat-tolerant germplasm: ‘Tiny Diamond’, ‘Secret Kiss’, ‘Red Twin’, ‘Tiny Icon’, ‘Orange Cocotte’, ‘Golden Matrix’, ‘Tiny Rocket’, ‘Tiny Moon’, ‘Matrix’, ‘Tiny Ghost’ and ‘Trendy Dakota’; and four lowly heat-tolerant germplasm: L. davidii var. unicolor, ‘Tiny Ink’, ‘Trendy Savannah’ and ‘Tiny Comfort’. Under short-term heat stress during the budding stage, the leaves and buds of highly heat-tolerant germplasm showed relatively large increase in proline content and antioxidant enzyme (superoxide dismutase, peroxidase, catalase) activities, relatively small increase in hydrogen peroxide content, and varying extent of increase in relative electrical conductivity. The short-term simulated high-temperature heat tolerance evaluation based on the results of principal component analysis, membership function, and cluster analysis was basically consistent with the results of long-term heat stress evaluation. Comparisons indicated that the long-term natural high-temperature heat tolerance evaluation was relatively comprehensive and accurate and was in line with production practice. The short-term simulated high-temperature evaluation reflected the stress response of plant when exposed to high temperatures and partially reflected their true heat tolerance.

Key words: Lilium davidii var. unicolor, Lilium Asiatic hybrids, heat tolerance, heat damage index, physiological indexes, principal component, membership function, cluster analysis