The Response of Stevia (Stevia rebaudiana Bertoni) Photosystem II Photochemistry to Fungi Symbiosis and Spermidine Application under Saline Water Irrigation

Abstract

Since the medicinal plants mainly are cultivated in marginal areas, are exposed to environmental stresses such as salinity, more than other plants. Salt stress causes damage to photosynthetic process, carbohydrates assimilation and photosystem I and II. However, recently, the role of fungi coexistence and polyamines in plants tolerance to saline conditions are pronounced. Therefore, the present study was conducted to evaluate the effects of endophyte symbiosis and spraying of polyamine spermidine (Spd) on chlorophyll fluorescence parameters of stevia (Stevia rebaudiana Bertoni) medicinal plant under irrigation with saline water. Treatments included non-inoculation (Control) or co-inoculation of Piriformospora indica + Trichoderma virens (Pi + Trich), foliar application of Spd (0 and 0.75) and three salinity levels of Caspian sea water (0, 6 and 12 dS m–1). Seedlings of stevia were transplanted in field conditions and were sprayed with Spd solutions after 9 weeks of planting. Seven days later, the plants were irrigated with three saline treatments for two weeks. The results showed that the foliar application of Spd had a positive effect on Fm, Fv and Fv/Fm and negative effect on Y(NO). Irrigation of plants with saline water had an adverse effect on fluorescence parameters. However, fungi inoculation markedly increased Fm, Fv, Fv/Fm and Y(II) while decreased Fo, Y(NPQ) and Y(NO) in all levels of salt stress. Fungal inoculation and Spd application with 0.75 mM remarkably enhanced Fm. Generally, inoculation of endophytic fungi and Spd spraying improved the chlorophyll fluorescence parameters and adjusted adverse effects of salinity stress in stevia plants.