The effects of endophyte symbiosis and spermidine foliar application on chlorophyll fluorescence and photosynthetic pigments of stevia (Stevia rebaudiana Bertoni) medicinal plant under salinity conditions

To evaluate the effects of endophyte symbiosis and spraying of spermidine on chlorophyll fluorescence and photosynthetic pigments of stevia (Stevia rebaudiana Bertoni) medicinal plant under salt stress conditions, a factorial experiment was conducted based on completely randomized design with three replicates. The treatments consisted of salinity in three levels (0, 6 and 12 dS.m-1), fungal symbiosis treatments including four levels: non-inoculated (control), inoculation with Piriformospora indica (Pi), at Trichoderma virens (Trich) and co-inoculation of two fungi (Pi+Trich) and spraying of spermidine in three levels (0, 0.75 and 1.5 mM). Seedlings of stevia after inoculation with fungi were irrigated with tap water until the end of vegetative stage and then irrigated with saline water treatments containing mixture of distilled and Caspian Sea water. The spermidine was foliarly sprayed one week before salinity stress. The results showed that the inoculation of endophyte fungi had a positive effect on Fm, Fv and Fv/Fm. The most increase of these parameters recorded when two fungi (Pi+Trich) were coinoculated. Also, fungi inoculation increased Y(II) while decreased Y(NPQ) and Y(NO) at different salinity levels. Fungal inoculation particularly Pi+Trich and spermidine application with 0.75 mM markedly increased Fm, Fv and Fv/Fm. Also, in all levels of salt stress inoculation with fungi as well as interaction of fungi and spermidine increased chlorophyll a content. In general, inoculation of endophytic fungi particularly co-inoculation of P. indica and T. virens, improved the chlorophyll fluorescence parameters and adjusted adverse effects of salinity. Also, the spermidine (especially at the rate of 0.75 mM) induced salt stress tolerance in stevia plant and showed synergetic effects with endophytic fungi in terms of the mentioned parameters.