Growth, yield and anatomy of alpinia calcarata (<em>Heen Araththa</em>) as affected by irrigation frequency

Alpinia calcarata, often known as Heen Araththa, is a precious medicinal plant owing to its chemical properties in herbal treatments. The growth, yield and anatomical features related to the synthesis and accumulation of secondary metabolites of this plant are highly affected by drought stress. Therefore, this work investigated the influence of irrigation frequency on growth, yield and selected anatomical features of A. calcarata. Five levels of irrigation frequencies including daily watering (T1), 7-day (T2), 14-day (T3), 21-day (T4) and 28-day (T5) intervals were investigated in a protected plant house under controlled environmental conditions. A. calcarata rhizomes with a similar number of sprouting buds planted in common potting media (topsoil: sand: compost- 1:1:1) were arranged in Completely Randomized Design in triplicates. After three weeks of establishment, five distinct irrigation frequencies were implemented, with pots being watered daily up until that point. Growth and yield parameters (shoot height (cm), number of roots, number of shoots, number of leaves per shoot, leaf area (mm2), rhizome dry weight (g)) and the anatomical parameters (root epidermis thickness (μm), rhizome epidermis thickness (μm) and oil cell density (μm2)) were collected 10 weeks after establishment. Data were analyzed using Analysis of Variance (ANOVA) employing the SAS analysis system. Results revealed that all selected growth, yield and anatomical parameters of A. calcarata were significantly (p<0.05) affected by irrigation frequency. Significantly (p<0.05) the highest mean shoot height (20.8cm), mean number of roots (11.3), mean number of shoots (6.8), mean rhizome dry weight (9.3g) and significantly (p<0.05) higher mean leaf area (24.9mm2) and mean number of leaves per shoot (4) of A. calcarata weregiven by 14-day irrigation frequency. It was also observed that the mean root epidermis and rhizome thickness of A. calcarata gradually increased in response to escalating drought stress. In contrast, the highest oil cell density was observed under the lowest drought stress. Based on the results, it can be concluded that the most promising irrigation frequency for higher growth and yield of A. calcarata is watering with 14-day intervals. Daily watering appeared to be the most suitable treatment to enhance oil cell density associated with secondary metabolite production of A. calcarata.