Morphological, physiological, and anatomical responses of Cattleya labiata Lindl. plantlets to mannitol-induced drought stress under in vitro conditions

Cattleya labiata Lindl. is a high-value ornamental orchid whose growth and development are highly dependent on adequate water availability. Drought stress disrupts cellular water balance, reduces photosynthetic activity, and restricts plant growth. Under in vitro conditions, drought stress can be simulated by incorporating mannitol into the culture medium as an osmotic agent. This study evaluated the effects of different mannitol concentrations on the morphological, physiological, and anatomical responses of C. labiata plantlets cultured in vitro. The experiment was arranged in a Completely Randomized Design (CRD) with five mannitol concentrations (0, 50, 100, 150, and 200 mM), each with five replications. The evaluated parameters included plantlet survival, morphological characteristics (root length, plantlet height, and leaf number), chlorophyll content, and stomatal density. Quantitative data were analyzed using analysis of variance (ANOVA), followed by Tukey’s Honestly Significant Difference (HSD) test at the 5% significance level. Mannitol concentrations ranging from 50 to 200 mM did not significantly affect plantlet survival, morphological growth, or chlorophyll content. In contrast, stomatal density decreased significantly with increasing mannitol concentration, indicating that anatomical responses were more sensitive to osmotic stress than morphological and physiological traits during the three-week culture period. These findings demonstrate that mannitol effectively induced drought stress responses in C. labiata plantlets under in vitro conditions, although the applied concentrations were insufficient to produce significant morphological and physiological alterations within the experimental period.