Effects of drought stress on morpho-physiological traits and mucilage yield in nine genotypes of Alcea rosea L

Hollyhock ( Alcea rosea L.) is an important medicinal and ornamental species characterized by high genetic diversity and mucilage content; however, its response to drought stress remains insufficiently understood. In this study, nine genotypes (‘Isfahan 1’, ‘Isfahan 2’, ‘Tabriz’, ‘Khomeini Shahr 1’, ‘Khomeini Shahr 2’, ‘Shahin Shahr’, ‘Shiraz 1’, ‘Shiraz 2’, and ‘Mahallat’) were evaluated under three irrigation regimes using a randomized complete block design. Drought stress (I3 vs. I1) significantly reduced vegetative growth, 1000-seed weight, and seed yield, while enhancing mucilage accumulation by 26% in leaves, 93% in petals, and 291% in seeds. In contrast to typical stress responses, chlorophyll content increased under severe drought, suggesting a compensatory acclimation mechanism. Clear genotypic differences were observed. ‘Khomeini Shahr 1’, ‘Tabriz’, and ‘Isfahan 2’ exhibited greater drought tolerance, maintaining higher growth, physiological performance, and yield stability under water-limited conditions. In contrast, ‘Shiraz 1’ and ‘Shiraz 2’ were identified as the most sensitive genotypes. Importantly, increased mucilage production under drought stress was not consistently associated with reduced yield, indicating a genotype-dependent relationship rather than a strict trade-off. These findings highlight the potential for selecting drought-tolerant genotypes that combine yield stability with enhanced production of bioactive compounds, offering valuable implications for hollyhock cultivation in arid and semi-arid regions.