INFLUENCE OF THE TIMING OF THE APPLICATION OF SALICYLIC ACID ON THE QUANTITATIVE YIELD AND SOME BIOCHEMICAL CHARACTERISTICS OF BARLEY (Hordeum vulgare L.) UNDER DEFICIT IRRIGATION

Using salicylic acid (SA) to feed drought-stressed plants plays a vital role in reducing the adverse effects of water stress and improving plant performance. This study explores the role of salicylic acid and different barley cultivars in mitigating the effects of drought stress on barley.The study examined three irrigation levels—one-time irrigation (severe stress), two-time irrigation (moderate stress), and four-time irrigation (control)—along with foliar and non-foliar applications of salicylic acid (SA) at three key stages of the Zadoks Growth Scale (ZGS): ZGS 29 (end of tillering), ZGS 34 (50% stem elongation), and ZGS 39 (completion of flag leaf emergence). These treatments were applied to three barley cultivars—Khatam, Reyhan, and Nosrat— which are considered semi-tolerant to drought stress. The findings showed that the interaction of reduced irrigation and SA increased chlora (8.8%) and b (7.12%) in the ZGS34 treatment under control conditions compared to the treatment without SA. The proline content increased with increasing drought stress, with the highest proline content obtained at the end of the tillering stage in the control condition. Compared to the control, which had no foliar spraying, the specific leaf area increased by 3.8, 1.8, and 0.4%, respectively. Relative water content in Khatam (35.6%), Reyhan (33.3%) and Nosrat (30.5%) decreased with increasing stress in the control treatment compared to the minimum stress. The most sensitive cultivar to lack of irrigation was Khatam. The rate of yield increase by SA compared to the control was (10.33%) among the barley cultivars cultivated, the cultivar Reyhan had a comparative advantage in more measures, mainly when applied at ZGS29. In conclusion, SA improved the drought tolerance of the barley and increased the yield by improving the biochemical characteristics.