Biochemical and Physiological Response of Marigold (Tagetes Erecta L.) to Foliar Application of Salicylic Acid and Potassium Humate in Different Soil Growth Media

Marigold flowers have great importance in the horticultural sector as an ornamental plant that is used not only in flavoring of foods, but is also important in the pharmaceutical and medicinal industries. The current study was carried out in pots under greenhouse conditions to evaluate the response of marigold plants to foliar application of salicylic acid (SA) and potassium humate (KH) using two growth media. Physiological and biochemical parameters were extensively evaluated along with the oil and beta carotene production potential of marigold plants. Different concentrations of SA (50, 100, 150, and 200 mg L⁻¹) and KH (500, 1000, 1500, and 2000 mg L⁻¹) were applied as foliar application in different soil growth media. Applied SA and KH treatments significantly increased all studied vegetative growth parameters except plant height, which remained nonsignificant. Enzymatic antioxidant activities were also enhanced under applied treatments of SA and KH. These activities were increased in the case of KH up to 1500 mg L⁻¹, whereas this trend was recorded up to 200 mg L⁻¹ in the case of SA with the exception of catalase. Photosynthetic parameters and chlorophyll fluorescence were decreased with increased doses of SA up to 200 mg L⁻¹, but this trend was typically the opposite for KH in both growth media. The oil productivity of marigold flowers increased up to 100 and 1000 mg L⁻¹ of SA and KH, respectively, whereas the highest oil yield was recorded after application 1000 mg L⁻¹ of KH. Therefore, production of marigold flowers could be achieved using poor growth media like sand, and further studies concerning different alternative growth media, particularly ecofriendly and cheap materials, are needed.