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

Cumin (Cuminum cyminum L.) is an industrial plant whose quality is affected by foliar application and irrigation regimes. In the present study, a field experiment was designed to assess the responses of cumin to foliar nutrition with salicylic acid (SA), jasmonic acid (JA), paclobutrazol (PBZ), and chitosan (CS) treatments under drought stress in Sistan Agricultural and Natural Resources Research and Education Center during 2019-2020. This experiment was performed as split plots based on randomized complete block design with three replications. The irrigation regime included three levels according to the evapotranspiration percentage of reference plant (supply of 100%, 70% and 40% water requirement of the plant (WR)). Based on the results, drought stress negatively affected photosynthetic pigments, yield, and yield components. Morpho-physiological traits improved under drought stress and non-stress conditions following the foliar fertilization. Moreover, foliar nutrition, especially JA, PBZ, and SA, resulted in synthesizing more photosynthetic pigments and proline, rising antioxidant enzyme activity, and consequently increasing 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 without foliar application under non-stress treatment. Additionally, SA, JA, and CS applications under severe water stress showed the highest SOD activity. The effect of SA and JA was superior on RWC. PBZ application under non-stress conditions showed the highest seed yield (698.9 kg/ha).