Ⅲ-4. Radiation Chemistry & Biology

RIKEN Accel. Prog. Rep. 53

Approach toward isolating early-heading mutants from Tana Toraja
local aromatic rice “Pare Bau” irradiated with argonand carbon-ion beams
A. M. Okasa,∗1,∗2,∗3 M. Riadi,∗1 T. Sato,∗2,∗3 K. Toriyama,∗2 K. Ishii,∗3 Y. Hayashi,∗3T. Abe,∗3 and R. Sjahril∗1,∗4
Tana Toraja is a mountainous area in the northernpart of South Sulawesi, Indonesia. The area has been
known as an aromatic-rice-producing area.1) The aromatic rice cultivar “Pare Bau” has good grain quality
and fragrant aroma, making it relatively expensive inthe market, but it has several disadvantages including
late heading dates and long stems for modern farming
systems. The heading date can be determined by thebasic vegetative phase (BVP) and photoperiod sensitive phase (PSP).2) Indonesian rice cultivated in mountain areas has a relatively short PSP and relatively long
BVP. This study aims to isolate early heading mutant
lines induced by heavy-ion-beam irradiation.
Dry seeds of Tana Toraja local aromatic rice cultivar(Oryza sativa L. “Pare Bau”) were irradiated with carbon ions (30 keV/µm) and argon ions (300 keV/µm) in
the RI-beam factory, RIKEN Nishina Center, Japan.
Owing to a limited range of Ar-ion beams, seeds for Arion irradiation needed to be packed in a single layer.
For this purpose, a sponge was bedded as a bottom
plate in a plastic rectangular box (75 × 50 × 18 mm).
The doses of Ar-ion and C-ion irradiation were 10 and150 Gy, respectively.3,4) We investigated the heading
dates of Pare Bau lines irradiated with Ar and C ions
(PB-A and PB-C, respectively).
In May 2016, M1 seeds (1000 seeds of PB-A and 1000
seeds of PB-C) were germinated and sown in seedlingpots and grown in a greenhouse for three weeks. The
germination rates of M1 seeds were 53% for PB-C and
49% for PB-A, while that of the wild-type control was70%. The seedlings (94 PB-A and 79 PB-C plants)
were transplanted in the paddy fields of Hasanuddin
University (S: 5◦ 7′ 53.50′′ E: 119◦ 28′ 57.97′′ ; 20 m above
sea level) in June 2016. Owing to poor establishmentof seedlings, only small amounts of M1 plants (13 PBA and 13 PB-C plants) set more than 50 seeds inNovember 2016. In June 2017, 50 M2 seedlings perline were transplanted in the paddy field of mountainous Enrekang Regency (S: 3◦ 19′ 47.44′′ E: 119◦ 50′ 1.57′′ ;650 m above sea level) neighboring Tana Toraja Regency. Based on heading dates at least one week earlier ʢ<119 daysʣthan those of the wild-type control(>125 days), we selected 82 PB-A and 26 PB-C plants
as mutant candidates. From these M2 plants, we sampled M3 seeds with relatively large grain weights per∗1∗2∗3∗4

Faculty of Agriculture, Hasanuddin University
Graduate School of Agricultural Science, Tohoku University
RIKEN Nisina CenterCorresponding author- 211 -Fig. 1. Phenotypes of early-heading mutants induced byheavy-ion-beam irradiation in the paddy field of Enrekang Regency.

panicle from 18 lines of PB-A and one line of PB-C inOctober 2017. In May 2018, 50 M3 seedlings per line
were transplanted in the paddy field of Enrekang Regency. Heading dates of the M3 individual plants andwild-type control plants were recorded for the first 25
plants showing relatively early heading. The days toheading of the wild-type control was 126 to 130 days
with an average of 128 days, while those of the following nine lines were 108 to 126 days with an average of 117 to 121 days, which were over one weekless than that of the wild-type control (Fig. 1). Theselines are PB-A.5.3.45, PB-A.6.1.9, PB-A.7.1.30, PBA.12.2.4, PB-A.12.2.12, PB-A.14.2.14, PB-A.14.3.1,PB-A.14.4.3, and PB-C.20.1.49. We expect these lines
to contain mutant candidates. Genetic analysis will be
performed for M4 lines and their hybrids with the wild
type to investigate the mutated genes responsible forearly heading.
Acknowledgements
The authors would like to express their deepest
gratitude to the Directorate General of Resources
for Science, Technology and Higher Education (DGRSTHE), the Ministry of Education and Culture forEnhancing International Publication Program throughthe PMDSU Scholarship.
References

1) H. Sahardi, F. Djufry, Proc. National Seminar on Genetic Resources of Agriculture, (2013) pp. 1.34–43.
2) B. S. Vergara, T. T. Chang, The Flowering Response ofthe Rice Plant to Photoperiod: A Review of the Literature, 4th Edition (IRRI, Philippines, 1985).
3) Y. Hayashi et al., RIKEN Accel. Prog. Rep. 50, 27(2017).
4) Y. Hayashi et al., RIKEN Accel. Prog. Rep. 51, 238(2018).