Genetic Improvement of Grain Quality in Japonica Rice - Translational Genomics for Crop Breeding: Abiotic Stress, Yield and Quality - page 144

Fig. 9.1. (a) Husked rice grains of indica (long-grain) and japonica (short-grain) rice cultivars. (b) Grain-size
variation in Japanese japonica rice cultivars of non-glutinous rice: (a) a large-grain cultivar, Oochikara; (b) a
Japanese brewing cultivar, Gohyakumangoku. Rice grains were supplied by Dr. Ebana of the National Institute
of Agrobiological Sciences Genebank. (c) Appearance of chalkiness in grains of (a) normal type (no chalkiness),
(b) white-back type, (c) white-based type, (d) white-belly type, (e) white-core type, (f) milky-white type, and
(g) abortive type. White scale bars represent 1 mm. For a color version of this figure, please refer to the color plate.

prevalent than japonica rice, but japonica rice is
preferentially grown and consumed in the north-
ern parts of the Asian rice cultivation region,
which generally lie in the temperate region.
Japonica rice cultivars are predominantly grown
in Japan, Korea, some parts of China, south-
ern Europe, Australia, and California (USA)
(Mackill 1995). The area of japonica rice
grown in China has expanded over the past
two decades, from 11% of the total rice cul-
tivation area in 1980 to 29% in 2000. Con-
sumer preferences and demand have increased
japonica rice production in both northern and
southern China (Wei et al. 2009). In Japan,
South Korea, and Taiwan, most of the rice
grown is japonica rice. Southern Europe is the
largest area outside Asia where japonica rice is
consumed.
Rice cultivars are required to show high
yield and strong resistance to biotic and abiotic
stresses. Of late, grain quality has become the
primary consideration of consumers, the food
industry, and seed producers (Champagne et al.
1999; Fitzgerald et al. 2009). Grain quality in
rice largely determines market price and con-
sumer acceptance, so it is a major target in rice
breeding programs (Peng and Khush 2003; Liu
et al. 2008). An understanding of the genetic

factors that influence rice grain quality is nec-
essary to efficiently develop new cultivars with
the high quality demanded by consumers. In fact,
“grain quality” represents a set of complex traits,
each controlled by multiple genes (or quanti-
tative trait loci, QTLs) and largely influenced
by environmental factors. Since grain quality in
japonica rice shows varietal differences (Figure
9.1) (Nakagahra et al. 1997; Kim 2009), many
researchers have been trying to identify the asso-
ciated genetic factors. Before the development
of molecular marker technology in the 1990s,
most genetic studies focused on the character-
ization of mutant lines that differed in grain
appearance (Takeda and Saito 1980; Satoh and
Omura 1981). Even now, many researchers study
mutants with clear phenotypic differences in par-
ticular traits (Ryoo et al. 2007; Satoh et al. 2008;
Fujita et al. 2009; She et al. 2010). During the last
two decades, genome-sequencing projects have
provided new and powerful genetic tools such
as DNA markers (McCouch et al. 2002; IRGSP
2005; Yamamoto et al. 2010; Nagasaki et al.
2010; Arai-Kichise et al. 2011). The use of DNA
markers has facilitated the identification and
molecular cloning of rice genes involved in mor-
phological and physiological traits, including
grain quality (Yano 2001). In addition, progress