Abstract
Water stress significantly limits the growth and productivity of crops, particularly medicinal plants in arid and semi-arid regions. This study explores the use of salicylic acid (SA) as a means to enhance shallot (Allium hirtifolium) resistance to water stress, as well as improve growth, yield, and water use efficiency (WUE) under various irrigation levels. Conducted over three consecutive growing seasons in a field (2016-2019), The study was conducted as split plot based on randomized complete block design with four replications. Irrigation as the main factors included 100 % (full irrigation), 75 % and 50 % of plant water requirement and no irrigation (dryland) and SA foliar application as sub-factors including 0, 0.5, 0.75 and 1 mM in this study. After ensuring uniformity of variance of experimental errors for three years, composite analysis of data was performed for three years. The results of combined analysis of three-years data showed that water stress reduced several growth parameters, including plant height, leaf dimensions, bulb size, onion and grain weight, and yield. However, SA application notably mitigated these adverse effects. Specifically, applying 1 mM SA in dryland conditions, increased the pod diameter and 1000-seed weight by 10.17 % and 19.97 %, respectively. Also, in the condition of 50 % plant water requirement, 1 mM SA enhanced onion dry weight, daughter onion weight and plant height by 12.41 %, 21.68 % and 19.18 % respectively. Furthermore, shallot yield increased by 15.12 % in dryland and by 29.4 % under 50 % of the plant's water requirement with 1 mM SA. The WUE in the treatment of 50 % of the water requirement of the plant and the use of 1 mM SA increased by 19.1 % compared to the non-use. These findings suggest that applying 1 mM SA can be a viable strategy for improving the growth, yield, and water use efficiency of shallot plants under water-stressed environments.