Effect of Sodium Chloride (NaCl) on the Mycelial Growth and Ascospore Germination of Rhizina undulata, the Root Rot Fungus of Coniferous Trees

Rhizina undulata, the causal agent of Rhizina root rot, is a soil-borne fungus occurring on coniferous trees. The destruction of coastal forests caused by R. undulata infection has been mainly associated with bonfires at camping sites. However, Rhizina root rot was observed in the western coastal forests without fire. It was hypothesized that Rhizina root rot in this area might be closely related to the soil salinity, which can facilitate the growth and survival of R. undulata. So, the variation in sodium chloride (NaCl) resistance among isolates of Rhizina undulata was compared using liquid media containing different concentrations of NaCl ranging from 0 mM to 300 mM. Our results showed that, albeit of no growth at a higher concentration of NaCl (300 mM), most of R. undulata isolates were capable of germinating and grew at up to 100 mM, indicating that NaCl resistance varies among R. undulata isolates. It was further found that isolates from coastal areas seemed to be more tolerant to NaCl than those further away the coast. We demonstrated that R. undulata could be possible to survive in coastal areas, but was lower NaCl tolerance than other fungi.