Studies on the systematics of ectomycorrhizal fungi in axenic culture. IV. The effect of some selected fungitoxic compounds upon linear growth

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Abstract
When cultures of ectomycorrhizal fungi were grown on potato dextrose agar supplemented with either benomyl (10 μg/mL), cycloheximide (2 μg/mL), rose bengal (10 μg/mL), malachite green (2 μg/mL), or sodium chloride (10 mg/mL), characteristic differences in linear growth rate reduction were exhibited. These fungitoxic compounds were able to differentiate ectomycorrhizal fungi into three growth-response categories, namely sensitive, semitolerant, and tolerant, which reflected taxonomic affinity. Linear growth of the Russulaceae and species of Hebeloma, for example, was inhibited by benomyl (10 μg/mL), whereas members of the Boletaceae and most species of Cortinarius were tolerant and species of Tricholoma were semitolerant at this concentration. Lactarius, Leccinum, and most Suillus species were sensitive to cycloheximide (2 μg/mL); Laccaria, Rhizopogon, and most Hebeloma species showed tolerance. Hygrophorus and most Lactarius species showed sensitivity to rose bengal (10 μg/mL), whereas Cortinarius, Laccaria, Suillus, and some Lactarius species (section Dapetes) exhibited tolerance. Malachite green (2 μg/mL) inhibited species of Lactarius, whereas species of Suillus and Tricholoma were tolerant. Xerocomus, Rhizopogon, Hygrophorus, and most Tricholoma species were sensitive to sodium chloride (10 mg/mL), whereas tolerance was exhibited by most species of Suillus, Laccaria, and Hebeloma. The results reveal that growth responses to these fungitoxic compounds have potential as taxonomic characters for the differentiation and identification of isolates of ectomycorrhizal fungi. Key words: ectomycorrhizal fungi, fungitoxic compounds, cultures, identification, systematics.