Mutagenesis—A Potential Approach for Crop Improvement - Crop Improvement: New Approaches and Modern Techniques - page 160

available in RARF (Japan). Six new flower varieties have been developed using
this technology and marketed in Canada, Japan, USA and the EU since 2002. Oka-
mura et al. ( 2012 ) demonstrated that ion-beam radiation mediated breeding can
alter and improve petal color and shading; this leads to the success creating the
most glittering carnation ever by taking advantage of new mutagenesis techniques
combined with exploiting genomic information. Here, Nakayam et al. ( 2012 ) sum-
marized their ideas obtained from their successive ion-beam mutant studies that can
be generally applied to the generation of mutants as follows:
1. Because of cooperative and compensative biosynthetic regulation between a tar-
get and its related compounds, mutants in which the target compounds either
increased or decreased could be generated by ion-beam irradiation.
2. When multiple compounds are concerned in the expression of one phenotype,
different types of mutants occur among the same phenotype.
3. Structural changes of the target compound influence the physical, chemical and
physicochemical properties, such as light-absorption, co-pigmentation effect and
solubility, respectively, resulting in the acquisition of a novel phenotype.
GammaPhytotron
Genetic improvement by chronic irradiation is another important option of mutation
breeding technique, especially when a wide array of mutants and minimal growth
arrest are needed. Therefore, a chronic irradiation of living plant materials has been
favored to induce useful mutants in mutation breeding. Unfortunately, these kinds'
of facilities are scarce and only a few Asian countries including Japan, Malaysia,
and Thailand have operational chronic irradiation facilities such as gamma field,
gamma greenhouse, and gamma phytotron, respectively. There are still many fac-
tors to consider when operating these types of facilities such as security and man-
agement issues. For this purpose, Kang et al. ( 2010 ) constructed a new gamma
phytotron which can be occupied with living pot plants or cultured callus during
long periods of chronic irradiation at lower doses. The ionizing source is 60 Co with
the radioactivity strength of about 400 curies. The facility consists of an irradiation
room, a non-irradiation room, a glasshouse for acclimation, an operating room, and
an office. The total area of the irradiation room is about 104.16 m 2 . The target plant
materials for a gamma ray irradiation can be arranged from 2 m (612.9 m Gy/h) to
7 m (60.1 m Gy/h) from the 60 Co source at present.
For safety reasons, the building, where the 60 Co source is located, is surrounded
by concrete walls with 1.2 m depth and a twofold lead shielded door between the
control room and the irradiation room. Moreover, the irradiation room is equipped
with two CCD camera systems, which enable an inner situation check of the con-
trol room. The irradiation room and non-irradiation control room have automatic
control systems for various ranges of temperature (15-35 °C), humidity (50-80 %)
and light condition (maximum 30,000 lx), which can be finely setup according to