Volume 19 Part 1 Article 82
Title: Induction of salt tolerance in Rhizopogon roseolus by ethyl methanesulfonate
Author: Qi Gao, Shota Nakano, Tadanori Aimi and Norihiro Shimomura
Rhizopogon roseolus (Corda) Th. M. Fr. (=R. rubescens Tul. & Tul.), known as “shoro” in Japanese, is a hypogeous basidiomycete and an important ectomycorrhizal symbiont of Pinaceae. Recent studies have suggested that ectomycorrhizal fungi play an important role in protecting host roots from environmental stresses such as high concentrations of heavy metals and salts. However, little is known about fungal strains that promote host defense mechanism against environmental stresses. Moreover, no mutagenesis studies on the selection of salt-tolerant ectomycorrhizal of R. roseolus strains have been performed. Here, to induce mutations, we treated two structures, the basidiospores and the homokaryotic mycelial fragments, of R. roseolus with ethyl methanesulfonate (EMS), a widely used chemical mutagen, and subsequently spread the cultures on diluted Modified Melin-Norkrans agar plates. On recovering the strains, we evaluated their salt-tolerance. Following EMS treatment, the number of colonies of isolates derived from the EMS-treated basidiospore suspension and homokaryotic mycelial fragments decreased in a concentration-dependent manner. We recovered R. roseolus strains from basidiospores and homokaryotic mycelia growing on both EMS-free media and EMS-containing media. The recovered strains were cultured on agar medium containing 0 mM NaCl and on that containing 300 mM NaCl. Among the isolates recovered from basidiospores grown on EMS-containing media, we identified salt-tolerant and salt-sensitive strains that showed a more vigorous or weaker mycelial growth in medium containing 300 mM NaCl, compared to that observed with the isolates derived from basidiospores grown on EMS-free media. Although salt-tolerant isolates derived from EMS-treated homokaryotic mycelial fragments were observed as well, most of these showed a significantly negative mycelial growth in medium containing 300 mM NaCl, compared to that observed with the parent strain. These results suggest that although the mutagen EMS may expand the salt tolerance of isolates derived from basidiospores, it induces negative mutation in isolates derived from homokaryotic mycelial fragments of R. roseolus.