Ⅴ. EVENTS
RIKEN
Accel. Prog. Rep. 56 (2023)

RIKEN Accel. Prog. Rep. 56 (2023)

The 10th users’ meeting on mutation breeding in RIBF “Sustainablesociety and creation of specialty products realized byion-beam breeding”
T. Abe,∗1 Y. Hayashi,∗1 Y. Watanabe,∗1 N. Fukunishi,∗1 K. Ishii,∗1,∗2 K. Tsuneizumi,∗1 Y. Shirakawa,∗1S. Ohbu,∗1 and N. Asakawa∗1
The users’ meeting on mutation breeding in RIBF has
been held the RIKEN Symposium every two years since2003. Moreover, we have published the RIKEN Symposium abstracts and user reports. The 10th symposium was initially scheduled to be held in January 2022;
however due to the Covid-19 pandemic, it was postponed until January 19–20, 2023. The RIKEN Symposium was held in a hybrid manner with 32 on-site and50 online participants. Online participation from remote locations was eﬀective. The participants’ researchﬁelds were categorized by biology (development of fundamental technologies and gene isolation) and breeding as targets (microorganisms, trees, food crops andﬂowering plants). In the 10th meeting, there were notree-breeding researchers, and the number of microalgae
researchers increased. The proportion of other specialities remained relatively the same from recent trends(Fig. 1).1)

FlowerFood crop

Biology

MicrobeFig. 1. The specializations of symposium participants in2022.

The meeting featured ten presentations and two invited lectures on three research topics: developing
breeding techniques, identiﬁcation of novel genes using
mutants and analysis of gene function, and breedingnew varieties. The invited talks were on bioreﬁnery
using microalgae and upgrade concept of the RIBF accelerators. In addition, a tour of the accelerator facility
was conducted before the meeting.
(1) Development of breeding technology
It is clear that mutations at 30 keV/µm, which havea high mutation rate in Arabidopsis thaliana, are often base substitutions or small deletions of a few bp.
Whereas those at 290 keV/µm, which have a high lethal
eﬀect, are often large deletions of 100 bp or more andchromosome rearrange- ments. Similar results wereobserved with rice.2) Furthermore,we investigated ge∗1
∗2

RIKEN Nishina Center
National Institute of Radiological Sciences, National Institutes for Quantum Science and Technology

Fig. 2. Photograph of on-site participants.

nomic mutations of carbon and argon ions at 100–300 keV/µm to identify the LETs that increase the rateof large deletions and chromosomal rearrangements in
Arabidopsis.
(2) Identiﬁcation of novel genes using mutants andanalysis of gene function
A sex-determining gene located on the Y chromosome
in a dioecious plant, Silene latifolia, was determined.3)
Other discovered genes can be used for seed size increase in Arabidopsis,4) heat-stress marker in rice5) andbreeding in wheat.
(3) Breeding new varieties
New varieties applied for variety registration in 2018–2022 were three cherry blossoms and one hibiscus by thefarmers, two Chrysanthemum that blooms in all threecolors during the Bon Festival by the Nagasaki Prefecture, and a Satsuma mandarin that can be harvested
one month late and suitable for long-term storage by
the Shizuoka Prefecture.
Users could deepen their understanding of accelerator facilities and accelerator science through invitedlectures and a tour of the accelerator. In the other special lecture, useful mutants, such as those yielding highoil production, have been obtained even in microalgae.
It was conﬁrmed that to realize a sustainable world, wewill continuously contribute to solving problems of energy, environment and food, and create local speciality
products by ion-beam breeding. The next meeting isscheduled to be held in January 2025.
References
1) T. Abe et al., RIEKN Accel. Prog. Rep. 53, 231 (2020).
2) R. Morita et al., Cytologia 86, 303 (2021).
3) Y. Kazama et al., Mol. Biol. Evol. 39, msac195 (2022).
4) V. Q. Nhat et al., Plants 10, 1252 (2021).
5) R. Tabassum et al., Plant Prod. Sci. 24, 230 (2021).

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