Genetic Improvement of Grain Quality in Japonica Rice - Translational Genomics for Crop Breeding: Abiotic Stress, Yield and Quality - page 152

Fig. 9.2. Eating quality QTLs on rice chromosome 3 in genetic populations derived from Japanese japonica
rice cultivar Koshihikari. Boxes and triangles indicate significant marker intervals and QTL peaks, respectively,
in (a) chromosome substitution lines derived from a cross of Koshihikari × Kasalath (Takeuchi et al. 2007), (b)
recombinant inbred lines of Sakihikari (a progeny cultivar of Koshihikari) × Nipponbare (Kobayashi and Tomita
2008), (c) recombinant inbred lines of Moritawase × Koshihikari (Wada et al. 2008), and (d) backcross inbred lines
of Nipponbare × Koshihikari (Takeuchi et al. 2008). Black bars and triangles indicate that the Koshihikari allele
of that region/QTL improves eating quality; while white triangles indicate that the Koshihikari allele decreases
eating quality. Abbreviations are as follows: GL, glossiness; TA, taste; ST, stickiness; HA, hardness; OE, overall
evaluation of cooked rice by sensory test; AC, amylose content; HP, hot-paste viscosity; CP, cool-paste viscosity;
CO, consistency viscosity; BD, breakdown viscosity by Rapid Visco Analyzer; AM, (glutamine + asparagine)/total
amino acid; HN, hardness/adhesion; HV, hardness/adhesiveness by texturometer.

Takeuchi et al. (2008) confirmed the genetic
effect of these Koshihikari QTL alleles by ana-
lyzing a chromosome segment substitution line
(CSSL) containing a Koshihikari segment of the
short arm of chromosome 3 in the genetic back-
ground of Nipponbare, a japonica rice cultivar
with inferior eating quality. The CSSL grain
was glossier, tasted better, was stickier, was
softer, and had a superior overall evaluation score
compared to Nipponbare (Figure 9.3). It also
had increased contents of the starch precursors
glucose-6-phosphate and fructose-6-phosphate
(Hori et al. unpublished data). Follow-up studies
such as fine-mapping, gene cloning, and pheno-
typic characterizations could reveal genetic fac-
tors underlying aspects of eating quality other
than amylose or protein content, and biochemical
measures of good eating quality conferred by this
chromosome region from Koshihikari. Thus, the
QTL localized on the short arm of chromosome
3 is an important target region for the develop-

ment of new japonica cultivars showing superior
eating quality in practical breeding programs.

Other Traits Affecting Grain Quality

The aroma of fragrant rice is of particular impor-
tance as it has a clear local and national identity.
Jasmine- and Basmati-style cultivars are widely
known types of indica fragrant rice from Thai-
land and India, respectively. More than 100 com-
pounds that contribute to rice aroma have been
identified; of these, 2-acetyl-1-pyrroline (2-AP)
is the primary component (Tsugita 1986; Brad-
bury et al. 2005). However, strong aroma traits
are not demanded of most japonica cultivars,
because aroma is not a preferred trait in japon-
ica cultivation areas.
Opportunities for improving the nutritional
value of rice grains have become increasingly
evident. Nutritional components such as min-
erals and vitamins are either absent or present