Morpho-physiological responses of cumin (Cuminum cyminum L.) to the application of growth regulators under drought stress

A field experiment was conducted as split plots based on a randomized complete block design with three replications to assess the responses of cumin (Cuminum cyminum L.) to foliar fertilization with growth regulators under drought stress. The study factors included three levels of irrigation regime according to the evapotranspiration percentage of reference plant (supply of 100%, 70%, and 40% water requirement of the plant (WR) as the main plot and 5 foliar treatments with salicylic acid (SA), jasmonic acid (JA), paclobutrazol (PBZ), chitosan (CS), and control (no foliar nutrition).Based on the results, drought stress negatively affected photosynthetic pigments, yield, and yield components while morpho-physiological traits improved under both drought stress and normal conditions following the foliar fertilization. Moreover, foliar nutrition, especially of JA, PBZ, and SA, resulted in synthesizing more proline and photosynthetic pigments, increasing antioxidant enzyme activity, and consequently improving yield components. The most positive effect of increasing chlorophyll content was related to the use of JA, which resulted in 27.9%, 29.4%, and 28.4% increase in chlorophyll a, b, and total, respectively. The highest SOD activity (3.89 U/mg protein) was related to the non-foliar nutrition under non-stress treatment. Additionally, SA, JA, and CS applications under severe drought stress showed the highest SOD activity. The effects of SA and JA were superior on RWC. PBZ application under non-stress conditions showed the highest seed yield (698.9 kg/ha). The lowest seed yield (103.4 kg/ha) was related to non-foliar nutrition under severe drought stress. The highest essential oil content (2.4%) was related to the JA application under severe drought stress (40% WR).