RIKEN Accel. Prog. Rep.
51 (2018)
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Ⅲ-4.
Radiation Chemistry& Biology
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Argon-ion-beam mutagenesis of the plant-symbiotic edible
mushroom Tricholoma matsutake †䠆䠆

H. Murata,∗1 T. Abe,∗2 H. Ichida,∗2 Y. Hayashi,∗2 T. Yamanaka,∗1 T. Shimokawa,∗1 and K. Tahara∗1areas.
Tricholoma matsutake is a ﬁlamentous fungus that
produces prized mushrooms “matsutake” in association with conifers.1,2) Currently, no cultivars allow thefungus to fruit artiﬁcially, unlike commercially available edible mushrooms. Developing cultivars that are
suitable for spawn cultivation will greatly contribute to
the artiﬁcial cultivation of the plant-symbiotic mushrooms. We hypothesized that irradiation breeding
could help produce T. matsutake cultivars for fruiting during spawn cultivation. In the present study, asa prerequisite for generating T. matsutake mutants, weFig. 1. Lethality of argon-ion beam on T. matsutake (n=3).
analyzed the lethality of an argon-ion beam (40 Ar17+ ,95 MeV/u) and generated mutants; this nuclide wasused because it has an LET of 280 keV/µm with atheoretical penetrating range in water of 8 mm, which䠆䠆should be suﬃcient to penetrate the fungal mycelialcolony on an agar plate.
An argon-ion beam (0–300 Gy) was irradiated on
T. matsutake mycelia on agar plates, after which hyphae at the edge of the colony were picked and transferred onto fresh agars, conferring a lethality rate proportional to the radiation dose (Fig. 1). Irradiation
with 100–150
Gy accelerated the killing, and that with
300 Gy exterminated the fungi (Fig. 1). Tricholoma
matsutake strain NBRC 33136, which had fewer aerial
hyphae, was more sensitive to the radiation, while
NBRC 108262 and NBRC 112911 with more aerial hyphae were somewhat resistant (Fig. 1). No putative
mutants were obtained based on mycelial morphology
during the lethality experiment. Therefore, we irradiated NBRC 33136 mycelia on agar plates at a doseof 500 Gy and picked pieces from an internal portionof the mycelia, rather than hyphae at the edge of thecolony; we hypothesized that with such a high dose,the hyphae in less populated areas would be killed
Fig. 2. Mycelial morphology on agar plates of putative
Mycelial morphology on agar plates of putativecompletely, while mutants might occur in densely pop- Fig. 2.
T. matsutake mutants. a The wild-type NBRC 33136.
ulated areas.
b–e Putative mutants whose phenotypes reverted to
The protocol conferred some putative mutants withthat of the wild-type after a culture transfer. f Putacolony morphologies diﬀerent from that of the wildtive mutant whose phenotype is relatively stable. Scaletype strain. Compared with the wild-type strain
bar: 5 mm.
(Fig. 2a), most of the putative mutants exhibited abtant, which had much fewer aerial hyphae and grewnormal traits at the ﬁrst screening, including thinsolely in a planar manner on MMN+V8 agar plates
mycelial colonies (Fig. 2b), increased numbers of aerial(Fig. 2f). While heavy-ion beams may be useful for
hyphae (Fig. 2c), hyphae that were bundled and grewisolating mutants of T. matsutake, maintaining murather straight (Fig. 2d), and hyphae that were erecttants requires precautions to prevent given traits from(Fig. 2e); however, they generally reverted to the wildreverting after repetitively culturing their mycelia.
type phenotype during the second screening. Despite
such a problem, we isolated one relatively stable muReferences†∗1∗21) L. Vaario et al., Mycorrhiza 20, 511 (2010).
2) A. Yamada et al., Mycoscience 55, 27 (2014).

Condensed from the article in Mycorrhiza 28, 171 (2018)
Forestry and Forest Products Research Institute
RIKEN Nishina Center- 244 -