Ⅲ-4. Radiation Chemistry & Biology

RIKEN Accel. Prog. Rep. 47 (2014)

Isolation of early-heading mutants induced by heavy-ion radiation in an
Indonesian native rice cultivar
E. Hanzawa,*1 Y. Kazama,*1 Y. Hayashi,*2 T. Abe,*2,*3 A. Higashitani*1 and T. Sato*1,*2
Rice is cultivated as far as 50º N in China and 40° S inArgentina. 1) The period from seeding to heading isimportant for cultivation over a wide latitude. The heading
time can be determined by the period of vegetative growthphase, from seedling to panicle primordium initiation, andreproductive phase, from panicle initiation to heading.2) The
vegetative growth phase consists of the basic vegetative
phase (BVP) and photoperiod sensitive phase (PSP).
Cultivated rice is classified as a short-day plant, and it
exhibits a wide genetic diversity with respect to sensitivity
to photoperiod 3). Tanisaka et al. isolated a longer BVP
mutant line induced by γ-irradiation of seeds of theJapanese lowland rice cultivar ‘Ginbozu’ with a longer PSP
and shorter BVP.3) Indonesian rice cultivars belonging to
the ecotype bulu have a shorter PSP and longer BVP.4) The
aim for this study was to isolate a shorter BVP mutant line
induced by heavy-ion radiation.
Dry seeds of an Indonesian native rice cultivar (Oryzasativa L. ‘Gemdjah Beton’ belonging to the ecotype bulu)
were irradiated with C-ions accelerated to 135
MeV/nucleon by (RRC) at a dose of 125 Gy in April 2011.
LET values of the C-ions corresponded to 22.5 keV/μm.
In 2011, the M1 seeds were sown in seedling trays at theend of April and grown in a greenhouse for 4 weeks. Field
experiments were conducted in the paddy fields of theExperimental Farm Station, Graduate School of Life
Sciences, Tohoku University, in Kashimadai, Osaki, Miyagi,Japan (37º28’, 141º06’). A fertilizer was applied to thepaddy fields at rates of 30 kg of N, P, and K/ha. We
transplanted 3,000 seedlings (age, four weeks) into a single
lot at the end of May. Plants were grown at a density of aplant per hill, with 30-cm spacing between hills. In themiddle of September, more than 15 M1 plants flowered one
week earlier than the other M1 plants and the wild-type‘Gemdjah Beton’. We sampled the M2 seeds of these M1
plants in the beginning of November.
In 2012, we planted the M2 seeds of these selected lines atthe end of April and then transplanted 50 seedlings per eachline in a paddy field at the end of May. One mutant line
flowered over about ten days earlier than the other M2 lines
and the wild-type in the middle of September. At the end ofOctober, M3 seeds of 26 plants were sampled in the M2 line.
*1

Graduate School of Life Sciences, Tohoku University*2RIKEN Nisina Center*3

RIKEN Innovation Center- 291 -In 2013, we randomly selected 10 M3 lines from 26 M3lines and grew 50 plants of each M3 line. The period fromtransplanting to the heading of wild-type was 17 weeks. Six
M3 lines exhibited the segregation from 15 to 17 weeks. The
heading day of two M3 lines was the same as that of thewild-type. All plants of another two M3 lines showedheading two weeks earlier than the wild-type. Therefore, wesucceeded in isolating early-heading mutant lines inducedby heavy-ion radiation.
Seven loci that control the period of BVP were detectedin cultivated rice.5) We are currently attempting todetermine the locus of the mutant gene that shortens theperiod of BVP in the mutant lines isolated in this study.

Fig. Early-heading M3 mutant line (left) and wild-type(right) grown in a paddy field on October 18, 2013
References
1) D. A. Vaughan: Wild relatives of rice. A Genetic resources
handbook. (IRRI, Philippines 1986).
2) B. S. Vergara and T. T. Chang: The flowering response of therice plant to photoperiod . A review of the literature. 4th Edition(IRRI, Philippines 1985).
3) T. Tanisaka et al.: Japan J. Breed. 42, 657 (1992).
4) N. Takahashi: in Biology of Rice, edited by S. Tsunoda and N.
Takahashi (Japan Scientific Societies Press, Tokyo, 1984), P 31.
5) Q. Yuan et al.: Theor. Appl. Genet. 119, 675 (2009)