Agronomic traits and fruit quality of milk thistle ( Silybum marianum ) genotypes under water stress

Abstract Milk thistle ( Silybum marianum (L.) Gaertn.) is an important medicinal plant, yet limited research has addressed its agronomic performance and genetic diversity under water‐limited conditions. This study evaluated the potential of 28 Iranian ecotypes and one foreign accession to assess variation in agronomic traits, oil concentration, and methanol extractable dry matter under normal irrigation and drought stress during two growing seasons. Drought stress reduced several yield‐related traits; however, some ecotypes, particularly those originating from southern regions of Iran, maintained relatively superior performance and showed comparatively higher oil content (9.2%–34.8%) and extractable dry matter (4.5%–14.6%). Correlation analysis indicated that the number of capitula per plant was the most important trait for indirect selection of yield. Under normal conditions, a significant negative correlation was observed between the number of achenes per capitulum and oil concentration, whereas this relationship changed under drought stress. A negative association was also detected between extractable dry matter and days to flowering. Multivariate analyses revealed clear patterns of genetic divergence among ecotypes and demonstrated the combined influence of genetic background and environmental conditions on trait expression. The results highlight the considerable variability within Iranian milk thistle germplasm and indicate its potential for cultivation and improvement under water‐limited environments.