The Alteration in Physiological Status, Growth and Essential Oil Profile of French Marigold (Tagetes patula L.) Owing to Seaweed Extract and Salicylic Acid Application

Abstract

Purpose: Medicinal plants show a relevant importance in human life and health. The use of natural substances in crop management is not only significant for the plant healthy growth and yield, but also for obtaining safe products. The study aimed to examine the effect of seaweed extract (SW) as a natural source of nutrition and salicylic acid (SA) on plant health, physiology and essential oil profile of French marigold (Tagetes patula L.). Methods: Three levels of salicylic acid, SA50, SA100 and SA200, (50, 100, and 200 mg L^{− 1}) and three levels of seaweed extract, SW2, SW4 and SW6 (2.0, 4.0, and 6.0 ml L^{− 1}), in comparison with control treatment (tap water) were applied as foliar sprayings. The seven treatments were arranged in randomized complete block design and were replicated thrice in two growing seasons (2020 and 2021). Results: Findings pointed out that SA200 increased plant height, branches number plant^{− 1}, stem diameter, leaf area, leaves number plant^{− 1}, plant fresh weight, and plant dry weight by 32.9, 112.2, 59.2, 34.4, 44.3, 33.0 and 56.9% (averages of the two seasons), respectively, compared to the control treatment (tap water). SW6 increased carotenoids content by 34.8 and 46.4% in 2020 and 2021 seasons, respectively. Salicylic acid at the rate of 200 mg L^{− 1} along seaweed extract at 6 ml L^{− 1} gave the highest values of total sugars and free amino acids. SA200 alone recorded the maximal value of peroxidase activity surpassing the other treatments. SW6 possessed the greatest essential oil content in both seasons, statistically equaling SA200 in the first season. Huge variations in essential oil profile were recorded under the tested trial treatments. Conclusion: It could be concluded that salicylic acid and seaweed extract foliar application unveiled their involvement in diverse physiological and developmental responses; pigment formation, enzyme activities, flower induction, nutrient uptake, essential oil metabolism, and overall plant growth and development. It is recommended to use the highest concentrations of the tested substances (SA at 200 mg L^{− 1} or SW at 6.0 ml L^{− 1}) for achieving distinctive improvements in physiological responses of French marigold plant.