Cytological and morphological responses of the ectomycorrhizal fungus <i>Rhizopogon roseolus</i> to saline conditions

Ectomycorrhizal (ECM) fungi are widely recognized for their ability to enhance plant survival and growth under saline conditions. Although extensive research has focused on the development of salt-tolerant ECM fungal strains, the cytological and morphological responses of ECM fungi to salt stress remain unclear. Moreover, the cellular mechanisms underlying fungal adaptation to high-salinity conditions remain poorly understood. This study investigated salinity tolerance and cellular adaptations of three <i>R. roseolus</i> strains subjected to increasing artificial seawater concentrations. The mycelia were grown on modified Melin-Norkrans (MMN) medium containing 0%, 50%, or 100% artificial seawater then observed under a phase-contrast light microscope. The hybrid strain TUFC102052 exhibited the highest tolerance to 50% artificial seawater, whereas significant growth inhibition was observed in both the wild-type strain TUFC10010 and the salt-sensitive strain TUFC102053 at higher salinity levels. Cellular alterations including subterminal cell size reduction and vacuole fragmentation were observed, indicating potential adaptive strategies for survival under saline conditions. These findings provide new insights into the morphological adaptations of the ECM fungus <i>R. roseolus</i> to salt stress.