Ⅲ-4. Radiation Chemistry & Biology

RIKEN Accel. Prog. Rep. 53

Mutation induction in strawberry of original Saitama cultivar by C-ion
irradiation
H. Uchida,∗1 H. Oda,∗1 E. Kondo,∗1 Y. Hayashi,∗2 and T. Abe∗2
Agriculture in Saitama prefecture is in a poor situation owing to the aging of producers and the decreasein the number of new farmers. Strawberry is one of theimportant farm products of Saitama because of its highproductivity per unit area. We have been working on
the breeding of strawberry since 2008 to enhance theproduction of strawberry. We successfully produced ouroriginal cultivars “Saien I-1Go” and “Saien I-3Go” 1) andregistered them in February 2019. These cultivars havea rich taste with high sugar content and moderate acidity, as well as a good balance between sweetness andacidity. Therefore, the production of these cultivars isexpected to expand in the near future. On the otherhand, they have the disadvantaged of a late harvest period and low yield compared to general main varieties.
In addition, the peel color of “Saien I-3Go” darkens inthe warm season, which results in a reduced evaluationof the fruit appearance. To solve these problems, weconducted mutation breeding by using heavy-ion beams
and are in the process of developing promising lines withimproved yield factors such as an increased number offruit sets, an earlier harvesting season, and a desirable
peel color.
We used “Saien I-1Go” and “Saien I-3Go” for irradiation from 2015 to 2018. The seedlings were irradiatedwith C-ion beams (LET 22.5 keV/µm) at dose ranges of
10–30 Gy, 30–80 Gy, and 30–120 Gy in 2015–2016, 2017,and 2018, respectively. After irradiation, seedlings weregrown by cuttings. The survival rate was measured after
4 to 5 weeks, and the growth and changes in peel color
were observed after planting. Selected mutant lines werepropagated in a runner plant, and the stability of mutant
Table 1. Survival rate of “Saien I-1Go” and “Saien I-3Go.”

DoseSurvival rate (%)(Gy)

Saien I-1Go

Saien I-3Go

0

100.0

100.0

30

90.7

93.2

40

92.8

-60

78.3

61.9

80

60.0

-90-26.4120
4.4"Saien I-1Go" in 2017, and "Saien I-3Go" in 2018 The number of surviving plants was counted 4 ("Saien,*R RU 6DLHQ,*R ZHHNVDIWHULUUDGLDWLRQ
∗1∗2

Saitama Agricultural Technology Research Center
RIKEN Nishina Center

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Fig. 1. Peel color of a mutant of “Saien I-3Go” irradiated ata dose of 30 Gy.

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Fig. 2. High-branching mutant of “Saien I-1Go” irradiated at
a dose of 80 Gy.

traits was confirmed in the next year.
According to the result, both “Saien I-1Go” and “SaienI-3Go” survived even at a dose of 80 Gy or more. A previous study showed that the lethal dose 50 of C-ion irradiation for apple and Japanese pear scions are 18 Gy and13 Gy, respectively.2) This suggests that the seedlings ofstrawberry may be a viable plant species even at highirradiation doses relative to those of other plants of thefamily Rosaceae (Table 1).
We obtained several mutant lines in this study. One ofthese mutant lines changed the peel color from dark red
to light red (Fig. 1). Another line increased the number of branches and flowers owing to abnormal branching morphology (Fig. 2). We are currently investigating
the other characteristics of these promising mutant lines,
such as the grass shape, flowering time, and yield. Weare also investigating whether the target trait is inherited in progeny and examining whether it is promising
as a breeding stock.
The peel color of the mutant is lighter than that of thecontrol.
The number of branches and flowers increased in themutant.
References

1) H. Oda et al., Bulletin of the Saitama Agricultural Technology Research Center. jpn. 17, 7 (2018).
2) Y. Ito et al., RIKEN Accel. Prog. Rep. 37, 151 (2004).
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