Ⅲ-4. Radiation Chemistry & Biology

RIKEN Accel. Prog. Rep. 53

Characteristics of heavy-ion mutagenesis in cultivated strawberry
T. Wada,∗1 T. Sueyoshi,∗1 K. Oku,∗1 K. Shimomura,∗1 and T. Abe∗2
A cultivated strawberry cultivar “Fukuoka S6” hasbeen a popular product in the Japanese strawberry market due to its high quality, which is attributed to desirable characteristics, such as large, deeply red, glossy andtasty fruits. However, this cultivar also has some disadvantages, such as late maturity and a soft fruit pericarp,which causes physical damage to the fruit while transporting. Ion-beam irradiation has attracted much attention as a novel technique for inducing spotted mutagenesis on plant genomes.1) This study developed mutantsof strawberry, which show early ﬂowering and high fruitﬁrmness, by using heavy-ion-beam irradiation.
An experiment was performed in 2014 and 2015. In2014, strawberry nursery seedlings (5 plants per treatment) propagated in a sterilized condition were exposed
to a 12 C6+ ion-beam (1.62 GeV, LET 30 keVµm-1) at theRIKEN Ring Cyclotron at doses of 0 (no treatment), 10,15, 20, or 30 Gy. In 2015, seedlings were propagated similarly, separated, and ﬁlled up in a 50-ml falcon tube (at7 g per tube). Eight tubes per treatment were exposed
to a 12 C6+ ion-beam. Irradiated seedlings were transplanted and cultured on 1/2MS media at 20◦ C with a
16-h light regime, the weight of seedlings after 2 months
from transplanting were measured, and the propagation ratio was calculated in comparison with the initialweight. The eﬀect of each treatment was evaluated bycomparing the propagation ratio to that achieved without treatment. Surviving seedlings were potted, acclimated, and transplanted in a greenhouse. The characteristics of mutants were examined using “Fukuoka S6”
as a control.
The propagation ratio decreased with an increase in irradiation dose, but the propagation ratio at 30 Gy, which
was the highest dosage, was 74% of that achieved without treatment (Fig. 1). Although many previous studies
using cultivated strawberry adopted a dosage of approximately 10 Gy, such as 8 to 16 Gy,2) 10 to 20 Gy,3) and
0.5 to 2.5 Gy,4) to obtain mutants in a practical breeding

Table 1. Characteristics of strawberry seedlings mutated bycarbon-ion-beam irradiation.
Trait
Fruit color
Fruit size

∗1
∗2

Fukuoka Agric. Res. Cent.
RIKEN Nishina Center

Total
75061

Fig. 2. Fruits of a mutant line developed from 15 Gy heavyion-beam irradiation (left) and “Fukuoka S6” (right).
Bars = 1 cm.

program, the median lethal dose (LD50 ) has not been
detected. The survival ratio at 32 Gy of 12 C6+ ionbeam irradiation was 91%,2) suggesting that the LD50of strawberry is greater than 30 Gy. Since the genome ofstrawberry was allo-octoploid (2n = 8x = 56), genes ona homoeologous genome might have compensated for theloss of functions of a certain gene. Summarizing thoseprevious studies and this study, the practical and suitable dosage of 12 C6+ heavy-ion-beam irradiation to obtain mutants of cultivated strawberry eﬃciently should
be further investigated.
Some surviving plants indicated characteristics different from “Fukuoka S6” in the forcing culture of thegreenhouse (Table 1). The fruit-pericarp pigmentationof mutants varied widely from darker red to lighter red(Fig. 2), but the fruit size only showed downsizing; further, some mutants showed harder fruit ﬁrmness thanthe control.
References

Fig. 1. Propagation ratio of strawberry seedlings mutated bycarbon-ion beam irradiation.

Darkening
Lightening
Upsizing
Downsizing

Absorbed dose (Gy)
10 15 203012131
4000000
12 23 10151) A. Tanaka et al., Genes Genet. Syst. 72, 141 (1997).
2) N. Chiba et al., JAEA-Review 2008-055, 78 (2008).
3) T. Abe et al., Breed. Res. 16, 67 (2014).
4) M. Yotoriyama et al., JAEA-Review 2010-065, 71(2011).

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