Ⅲ-4. Radiation Chemistry & Biology

RIKEN Accel. Prog. Rep. 53

Breeding of summer-autumn-flowering small-flowered spray-type
chrysanthemums cultivar ‘Nagasaki SWC1’ by heavy-ion-beamirradiation
A. Hisamura,∗1 J. Morooka,∗2 T. Abe,∗3 Y. Hayashi,∗3 and T. Hirano∗3,∗4
In Nagasaki Prefecture, the small-ﬂowered spray-type
chrysanthemums is promoted for planting in open ﬁelds
because producers can cultivate it at low cost. It has agreat demand during Obon (early in August) as a funeral ﬂower in Japan. It is necessary to ship three colors of ﬂowers (red, white, and yellow) simultaneously
from the market. However, the shipment time is unstable because of bloom delays or bud departing at theearly stage caused by high temperatures during the cultivation period. Therefore, the development of a new
cultivar that enables a stable shipment time has been
desired to meet the needs of the market. We conductedcross-breeding and selected a superior red lineage forwhich the blooming time can be controlled using longday treatment under lighting (Fig. 2(a)). In this study,
we irradiated this superior red lineage with a heavy-ion
beam to obtain cultivars of diﬀerent colors that have thesame shipment time as the superior red lineage. It has
been reported that the ﬂower color of the original cultivar is important to obtain a wide mutation spectrumof the ﬂower color in Chrysanthemum.1) This cultivar
was thought to be suitable for inducing mutations ofthe ﬂower color such as white or yellow. As a result,
we succeeded in developing a new cultivar known as“Nagasaki SWC1” with white ﬂowers in 2018.
We irradiated 27 scions of the superiod red lineagewith C-ion beams (LET: 23 keV/µm) at a dose of 5 Gy
at RIKEN Nishina Center in January 2015. We plantedand pinched the irradiated scions as a mother stock, following which we picked scions. We planted these scions
in the ﬁeld and obtained 984 candidate mutant plants,
including 49 ﬂower-color mutants. Some of these mutants were chimera. Therefore we isolated the plants
with only white ﬂowers in the ﬁrst selection. We multiplied these plants and cultivated them in the ﬁeld in2016. Subsequently we selected a superior plant named“W1-1” in the second selection. The third selection wasperformed in 2017 to conﬁrm its stability of characteristics and ﬂower color. The ﬁnal experimental productionof “W1-1” was performed at the ﬁeld of an agricultural
center, and “W1-1” gained high evaluation in a test ofadaptability to local ﬁelds in 2018. We named this superior cultivar “Nagasaki SWC1” and applied for theregistration of this variety on March 18, 2019.
“Nagasaki SWC1” has a white (white-group 155-C
on the R.H.S. color chart) single ﬂower (Fig. 2(b)). It∗1∗2∗3∗4Agriculture and Forestry Technical Development Center, Nagasaki Prefectural Government
Shimabara Development Bureau
RIKEN Nishina Center
Faculty of Agriculture, University of Miyazaki

Fig. 1. Original flower and the flower-color mutants.

Fig. 2. Original flower (a) and a new cultivar “Nagasaki
SWC1” (b).

blooms in the middle of July under natural long days.
It is also possible to control blooming by long-day treatment under light culture and adjust the shipment timeto the period of highest demand which is early August. Furthermore, “Nagasaki SWC1” has a small unnecessary inferior branch. This characteristic provides
a labor-saving plant shape which is suitable for bouquet
making. These characteristics of “Nagasaki SWC1” areinherited from the superior red lineage. Therefore, red
and white ﬂowers can be shipped simultaneously in theperiod of highest demand. This is a great advantage for
producers, and an increase in their income can be expected. Presently, we are working on breeding a yellow
ﬂower line. Our aim is to breed a new cultivar for a setof three colors of small-ﬂowered spray-type chrysanthemums.
Reference1) K. Tamaki et al., Hort. Res. (Japan) 16, 117 (2017).

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