III-4. Radiation Chemistry & Biology

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Selection of high-yield rice mutant induced by heavy-ion beamirradiation
Y. Hayashi,∗1 Y. Shirakawa,∗1 K. Ichinose,∗1 R. Morita,∗1 T. Sato,∗1,∗2 and T. Abe∗1
Improvement in productivity is the main objective ofrice breeding. Rice grain yield is determined based on
three components: the number of panicles per plant,
number of grains per panicle, and grain weight. Amongthem, the grain weight is a stable varietal character andeﬀective target trait for the mutation breeding of highyield rice.
We performed mutant selection for achieving highyield rice from M2 populations obtained by heavy-ion
beams irradiation. M2 seeds used in this study were
derived from irradiated dry rice seeds of ‘Nipponbare’(Oriza Sativa L.) with C-ion, Ar-ion, and Fe-ion. Linerenergy transfer (LET) and irradiation doses are summarized in Table 1. These conditions were the most eﬃcientwith the highest mutation rate at each LET in our previous study.1,2)
There were 790 M1 lines in total and ten plants fromeach M1 line were planted in the paddy ﬁeld. In our previous study on rice, we isolated various mutants of theﬂowering period, plant height, leaf color, tillering, andweakness by visual evaluation in the paddy ﬁeld. However, the identiﬁcation of grain size in the ﬁeld for mutant
selection is not easy and is ineﬃcient. Panicle weightreﬂects the grain size and fertile grain number, which
are two major components of the yield. We adopted themethod of measuring the weight of the main panicle fromeach M1 plant to select the candidates of the mutant.
First, some lines were excluded from panicle weight selection when segregated mutations were observed in theﬁeld. We selected 18 candidates based on panicle weightfrom 462 M1 lines (Table 2).
Next year, we conducted a yield survey on a small
scale to conﬁrm their traits and narrow down the candidates. Thirty M3 seedlings of each candidate line wereplanted in a plot (0.9 m wide and 3 m long). ‘Nipponbare’ was used as control. To avoid the border eﬀect, 8plants from the inner plot (2.4 m2 ) were collected. The
panicle weight, spikelet number, seed fertility, and grain
weight were investigated on the main culms. The grainsfrom the line with the higher weight were dehulled; theTable 1. Irradiation conditions of heavy-ion beams.
Energy(MeV/nucleon)
C135
Ar (184)
160
Ar (290)
95
Fe
90Ion

LET(keV/µm)
30
184
290
650

Dose(Gy)
175
201020

Table 2. Number of lines selected in each generation.
IonCAr (184)Ar (290)
FeTotalPlanted
M1 line200200200
190
790

Surveyed
M1 line113121122106462

Candidates
M2M352404152
185

grain width, grain length, and grain thickness were measured using a rice analyzer (RGQ1 10B, SATAKE). However, some lines which had low fertility or low number ofgrains were not included in the grain size measurement
even though their grain weight were high, because thetrade-oﬀ relationship between the single grain size andgrain number should be considered. In addition, lines
with large individual diﬀerences were excluded. Finally,ﬁve lines were selected based on their large grain size.
There was a trend for long grains in all 5 candidates(Table 3). Among them, Ar-39 achieved the best resultsin most components. Our previous study succeeded indiscovering novel gene: LIN1 using the long grain mutant
induced by Ar-ion irradiation.3) The genetic analysis ofthese candidates to reveal relevant genes is in progress
while continuing repeated yield surveys on a large scale.
References

1) Y. Hayashi et al., RIKEN Accel. Prog. Rep. 50, 27 (2017).
2) Y. Hayashi et al., RIKEN Accel. Prog. Rep. 51, 238 (2018).
3) R. Morita et al., Molecular Breeding 39, 135 (2019).

Table 3. Mean ± standard error of yield-related characters and grain size for selected M3 lines.
Panicle weight Grain number Seed fertility Grain weight(g/one panicle)(/panicle)(%)(g/1,000 grain)‘Nipponbare’ 2.95 ± 0.07
130.4 ± 5.58
87.3 ± 1.86
24.2 ± 0.26
C-98
3.32 ± 0.14
135.6 ± 5.19
85.1 ± 1.44
25.0 ± 0.21
C-190
2.80 ± 0.06
118.0 ± 2.78
83.2 ± 1.70
25.8 ± 0.13
Ar-39
3.63 ± 0.14
148.8 ± 5.70
85.4 ± 0.89
25.7 ± 0.23
Fe-1343.10 ± 0.11
129.0 ± 3.91
83.5 ± 1.69
25.5 ± 0.17
Fe-1533.03 ± 0.10
126.6 ± 4.50
83.5 ± 1.48
25.2 ± 0.27
Line

∗1
∗2Length5.02 ± 0.03
5.08 ± 0.02
5.18 ± 0.02
5.17 ± 0.02
5.12 ± 0.02
5.08 ± 0.02

Grain size (mm)WidthThickness
2.81 ± 0.02
1.88 ± 0.01
2.77 ± 0.02
1.86 ± 0.01
2.85 ± 0.02
1.89 ± 0.01
2.89 ± 0.02
1.89 ± 0.01
2.85 ± 0.02
1.88 ± 0.01
2.85 ± 0.02
1.89 ± 0.01

RIKEN Nishina Center
Graduate School of Agricultural Science, Tohoku University- 173 -1