Evaluating Drought Tolerance in Codonopsis pilosula Seedlings: Combining Growth, Physiology, Yield, and Tolerance Indices

Drought stress during the <i>Codonopsis pilosula</i> (Campanulaceae) seedling stage significantly affects its growth, quality, and yield. The aim of this study was to identify drought-tolerant cultivars of <i>C. pilosula</i> by using the growth-physiology-yield composite index (GPYCI) and drought-tolerant indices. Nine <i>C. pilosula</i> cultivars were evaluated under normal-watered (black plastic film hole sowing, BF) and water-stressed (spread in the open field, SF) conditions in a design that adopted a two-factor paired experiment with three replications. The emergence rate was significantly influenced by the water treatment, while both the water treatment and the cultivar affected root length, proline content, APX activity, and chlorophyll levels. The G1 cultivar performed better than others in multiple aspects. Yields and their attributes varied among cultivars under different water levels. The average yield was 7350.76 kg/hm² under BF conditions and 4856.32 kg/hm² under SF conditions. Drought stress reduced the total root length, single root fresh weight, and yield by 18.33%, 28.4%, and 33.9%, respectively. Correlation analysis revealed unique physiological response mechanisms to water changes among cultivars. Drought tolerance indices and comprehensive factor analysis indicated varying levels of drought tolerance among cultivars. This study has provided valuable insights into the growth, physiology, and yield response of <i>C. pilosula</i> under drought conditions and laid the foundation for breeding drought-tolerant cultivars.