RIKEN Accel. Prog. Rep. 50 (2017)

Ⅲ-4. Radiation Chemistry & Biology

Effect of carbon-ion irradiation on the mycelial growth of Tricholoma
matsutake in the form of spawn
H. Murata,1 T. Abe,2 H. Ichida,2 Y. Hayashi,2 T. Yamanaka,1 T. Shimokawa,1 and H. Neda1Tricholoma matsutake is a filamentous fungus that
produces gourmet mushrooms, commonly known as“matsutake,” during mycorrhizal association with conifers,
most notably red pines Pinus densiflora in the Far East Asiaand Pinus sylvestris in Scandinavia. 1-3) Currently, neither
cultivars nor cultivation methods that allow T. matsutake tofruit artificially are available, unlike some wood-rotting
edible fungi, such as Lentinula edodes, commonly known as“shiitake,” and Pleurotus ostreatus, commonly known as“oyster mushroom.” Because we solely harvest the wild
fruiting body for trading, the matsutake yield has
devastatingly decreased over the past few decades in Japanand other countries that export the commodity. Developing
cultivars that are suitable for spawn cultivation to yieldmatsutake will greatly contribute to countermeasuresagainst overharvesting of the wild mushroom. Lyophyllum
shimeji, an ectomycorrhizal edible fungus that producesanother gourmet mushroom commonly known as “shimeji,”
are artificially cultivated for commercial trading after
selecting a few extraordinary strains suitable for spawn
cultivation. 4)
Since particle beams have been used widely in crop
breeding to generate superb cultivars and industrial
microbes with practical uses, we hypothesized thatparticle beams could be useful in breeding T. matsutake
cultivars for fruiting during spawn cultivation; note thatclassical breeding does not work on the fungus becauseof complex variable nuclear phases and the lack ofinformation on the mating system. 5) In the present study,
as a prerequisite for generating T. matsutake mutants, weanalyzed the lethality of carbon-ion irradiation and its
corresponding doses using the fungal spawn.

T. matsutake mycelia were cultured as spawn in amayonnaise jar according to a protocol for L. shimeji (Fig.
1), 4) which could be more practical for cultivar selection
than agar plate culture. Prior to the irradiation, the spawn
was transferred into either a sterile plant tissue culture box(60 × 60 × 60 mm) containing sheets (10 mm thick) of
hardwood or a sterile plastic Petri dish (90 × 15 mm) so thatthe particles pass through the spawn (Fig. 1). After
irradiation, the spawn was divided into 10 portions as seeds,inoculated into fresh sterile substrates, and incubated at 22o
C for 60 days (Fig. 2). The extent of mycelial growth in thespawn was scored (Fig. 2).

Fig. 2. T. matsutake growth after the carbon-beamirradiation. The irradiated spawn was divided as seeds,inoculated into fresh substrates and incubated for 60 days.
The 300-Gy irradiation dose resulted in little growth, as
the fungal mycelia only colonized the inoculated area on thesurface, while the 150-Gy dose resulted in growth to acertain extent by thinly invading the substrate (Fig. 2). In
the controls, the fungal mycelia grew well throughout thesubstrate (Fig. 2). Therefore, we conclude that the carbon
ion irradiation may be useful in generating mutants from T.
matsutake that is cultured as spawn with a barley
grain-based substrate.
References

Fig. 1. T. matsutake spawn. The mycelia axenically cultured
in a mayonnaise jar (left) were transferred to a sterile planttissue culture box (right) for irradiation.
1
2

Forestry and Forest Products Research Institute
RIKEN Nishina Center- 268 -1) L. Vaario et al., Mycorrhiza 20, 511 (2010).
2) A. Yamada et al., Mycoscience 55, 27 (2014).
3) M. Yamaguchi et al., Mycorrhiza 26, 847 (2016).
4) A. Ohta, Mycoscience 35, 147 (1994).
5) H. Murata et al., Mycoscience 56, 287 (2015).