Abstract
Drought is a significant environmental stressor affecting a broad range of ornamental plants. Selecting and developing drought-resistant ornamental plants is a key strategy to solve this problem. This study comprehensively evaluated the drought resistance of 25 Hemerocallis fulva genotypes, which were collected from natural populations along the Taihang Mountain range in Shanxi Province, China. Five growth indices and eight physiological parameters were measured both prior to and following drought stress exposure in plants. These parameters included total chlorophyll (Chl) content, Chl a and Chl b contents, the Chl a/b ratio, carotenoid content, leaf relative water content (RWC), electrolyte leakage, and malondialdehyde (MDA) content. The results indicated that drought stress led to a reduction in plant height, canopy width, as well as leaf length, width, and area. Interestingly, under drought conditions, the contents of total Chl, Chl a, Chl b, and carotenoids, along with the Chl a/b ratio, generally increased, though the extent of these changes varied across different genotypes. On the other hand, the drought treatment resulted in elevated electrolyte leakage and MDA content, while RWC showed a marked decrease. To better understand the underlying physiological responses, Principal Component Analysis (PCA) was applied to condense the thirteen individual growth and physiological parameters into three principal components: (1) a plant growth index, (2) a photosynthetic pigments index, and (3) a comprehensive water status and cell membrane damage index. Based on the comprehensive evaluation scores, cluster analysis, and heatmap analysis, the 25 Hemerocallis fulva wild genotypes were categorized into three groups: high drought-resistance, moderate drought-resistance and low drought-resistance. Genotypes Taiyuan No.1, Taiyuan No.2, Qinshui No.1, Taigu No.1, Jiaocheng No.1 and Datong No.1 were classified as exhibiting high drought resistance. No significant correlation was observed between drought resistance and either chromosome ploidy or the number of flower petals in wild Hemerocallis fulva. Drought resistance showed a positive correlation with the Chl a/b ratio and a negative correlation with leaf electrolyte leakage. This study not only provides valuable genetic resources for landscape architecture in arid regions. Moreover, it establishes a comprehensive and reliable methodology for evaluating drought resistance across different Hemerocallis fulva genotypes.