Water deficit stress impairment of morphophysiological and phytochemical traits of Stevia (Stevia rebaudiana Bertoni) buffered by humic acid application
Hadiseh Khorasani, Faezeh Rajabzadeh, Hamid Mozafari, Abdollah Ghasemi Pirbalouti
Abstract
In sustainable agriculture, the foliar application of humic acid can be an effective solution in reducing the adverse effects of water deficit conditions in crops without damaging the environment. In order to investigate the effect of humic acid on the growth parameters and secondary metabolites of stevia (Stevia rebaudiana B.) under different soil moisture conditions, a study was done at the experimental filed of Western Tehran, Iran during the growing season 2018–2019. The experiment was performed as a factorial in a randomized complete block design. The experimental treatments included the foliar spraying of humic acid at three levels (0, 150 and 300 g/mL) and irrigation frequencies (3, 5, and 7 days based on irrigation at 80–85% of field capacity). The results indicated that with increasing interval irrigation, the plant height and stem fresh weight as well as the leaves dry and fresh weight decreased significantly: whereas, the use of humic acid (especially at the level of 300 g/mL) caused a significant improvement in these indices under reduced irrigation conditions. The highest amounts of the leaf area index (LAI) and carotenoid content were related to the application of 300 g/mL humic acid. The chlorophyll a and b contents and the concentrations of two main active substances such as stevioside and rebaudioside A contents in the leaves enhanced significantly under increasing interval irrigation. The highest amounts of the stevioside and rebaudioside A contents (41.5 and 11.6 mg/100 g dry matter, respectively) were obtained in the interval irrigation of 7 days and without humic acid. According to results of the interaction effects of the application of humic acid and irrigation found, the application of humic acid can improve plant biomass which can reduce the harmful impacts of deficit irrigation on the plant growth parameters of stevia:however, reduced irrigation without the foliar application of humic acid could increase the quality yield of stevia such as stevioside and rebaudioside A.