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K. Murai,∗1 Y. Kazama,∗2 and T. Abe∗2tetraploid�����
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derived from two wild diploid ancestral species: theA genome from T. urartu and the B genome fromAegilops speltoides or another species classiﬁed in
the Sitopsis section. Therefore, the tetraploid durum wheat genome contains duplicated homoeologous
genes, and this characteristic may increase the diﬃculty of screening for mutants in durum wheat. To
avoid this problem, we have chosen the use of cultivated diploid einkorn wheat (T. monococcum) with
the Am genome, similar to the A genome in breadwheat, for developing a large-scale mutant panel.1) andscreened and analyzed several mutants from the mutant panel.2) However, durum wheat is an importantcrop species for making pasta, and we have started tomake a mutant panel of durum wheat by heavy-ion
beam irradiation.
To avoid the rainy season for harvesting, early maturing is one of the important properties of breadwheat in East Asia, including Japan. Therefore, we
focused on identifying early-ﬂowering mutations in thescreening of the mutant panel.
Dry seeds of the durum wheat cultivar “Langdon”
were irradiated with 15, 30, or 50 Gy of 12 C6+ ions at
LET values of 30, 50, or 70 keV µm−1 , or 2.5, 5.0, 7.5,
10, or 20 Gy of 40 Ar17+ ions (290 keV µm−1 ) to determine the optimal conditions for mutant generation byusing the E5 beam line of the Ring Cyclotron (RRC) in
the RIKEN RI-beam factory. The M1 seedlings wereplanted in the ﬁeld in October 2014. The viability
rate for the Ar ion beam was reduced to less than 60%
with a dose greater than 7.5 Gy, and all plants diedwhen the dose was 10 or 20 Gy. The harvested seeds
from each individual M1 plant were used to produce
the next generation (M2 ) lines. 77–134 M2 lines (1068lines in total) for each LET-Gy combination were sownin October 2015 in the ﬁelds; ten seeds of each M2 line
were sown. The frequency of lines with albino plant(s)among the ten plants was determined to assess thecomparative mutation ratio of the diﬀerent irradiation
conditions. The frequency of albino plants in the M2generation was diﬀerent for diﬀerent LET-Gy combinations (data not shown). The highest ratio (>2.0%)
was observed for the LET50-30Gy treatment condition. On the other hand, the data of survival ratio∗1∗2

Department of Bioscience, Fukui Prefectural University
RIKEN Nishina Center
This work was supported by Council for Science, Technologyand Innovation (CSTI), Cross-ministerial Strategic Innovation Promotion Program (SIP), “Technologies for creatingnext-generation agriculture, forestry and fisheries.”- 239 -Fig. 1. Appearance of early-flowering mutant plants in M2
generation. Percentages (%) of M2 lines segregating
mutant plants are shown in each LET-Gy combination of ion-beam irradiation. Red and blue bars indicate moderately early-flowering and early-flowering mutants, respectively.

suggests that LET70-15Gy treatment was the optimal
condition for durum wheat.3)
In the mutant screening in 2016, we observed moderately early-ﬂowering mutation within a few days
and early-ﬂowering mutation before four days, compared with the wild-type. Figure 1 shows the percentages of the M2 lines segregating early-ﬂowering mutant(s). The moderately early-ﬂowering mutants wereobtained under relatively moderate treatment condition of LET70-15Gy with C, whereas early-ﬂoweringmutants were mainly obtained under harsher treatment condition of 5.0 Gy with Ar.
Durum wheat cultivars are usually late-heading andnot suitable for cultivation in Japan, because we havea rainy season from June to July. All known cultivars of durum wheat show pre-harvest sprouting whensubjected to prolonged rainfall before harvest. Furthermore, durum wheat cultivars are susceptible to
the Fusarium head blight disease. To develop durum wheat cultivars suitable for wide cultivation inJapan, we are focusing on identifying mutations ofearly-heading, short culm, and resistance against preharvest sprouting and Fusarium head blight in durum
wheat by using heavy-ion beam mutagenesis.
References
1) K. Murai et al., Nucl. Instrum. Methods Phys. Res. B
314, 59 (2013).
2) A. Nishiura et al., Breed. Sci. 64, 213 (2014).
3) K. Murai et al., RIKEN Accel. Prog. Rep. 50 (2017).