Response of Vanilla (Vanilla planifolia Andrews) to Osmotic Stress Induced by PEG 6000 Treatment

Vanilla (Vanilla planifolia Andrews) is a member of the Orchidaceae family with high economic value, yet it is highly sensitive to drought, which significantly hampers its cultivation. To simulate drought stress under controlled conditions, high-molecular-weight osmotic agents such as Polyethylene Glycol (PEG) are widely used. This study aimed to determine the maximum tolerable concentration of PEG 6000 for vanilla plants and to analyze their physiological responses, including chlorophyll a, b, and total content; stomatal index; total soluble carbohydrate content; reducing sugar levels; and stress tolerance index. The experiment was designed using a Completely Randomized Design (CRD) with five PEG 6000 concentrations: 0% (A1), 10% (A2), 20% (A3), 30% (A4), and 40% (A5). Data were analyzed using one-way ANOVA at a 5% significance level, followed by Tukey’s post hoc test. Results indicated that PEG 6000 concentrations up to 40% are still applicable for in vivo selection of vanilla plants. At this concentration, plants demonstrated drought tolerance as indicated by the stomatal index and stress tolerance index (STI). Increasing PEG 6000 concentrations reduced chlorophyll content (a, b, and total) while enhancing total soluble carbohydrate content in vanilla plants.