Biology Reference
In-Depth Information
Chapter 9
Genetic ImprovementofGrain Quality
in Japonica Rice
KiyosumiHoriand MasahiroYano
Abstract
Rice grain quality largely determines market price and consumer acceptance. Rice grain quality is
determined by a set of complex traits encompassing a wide range of physical and cooking characteris-
tics. In general,
japonica
rice consumers prefer short, translucent grains that are sticky and soft when
cooked. To improve the grain quality of
japonica
rice cultivars, many genetic studies of grain-quality
traits have been conducted and have revealed the involvement of multiple genes and quantitative trait
loci (QTLs). Grain size QTLs have been identified, and some responsible genes have been isolated
by means of map-based cloning. A number of QTLs were found for grain chalkiness traits induced
by high temperatures during the grain ripening stage. Several of these QTLs have been fine-mapped,
but no genes have been cloned yet. The pasting characteristics and texture of cooked rice are largely
influenced by grain components of amylose, amylopectin, and proteins. Genetic analysis of rice en-
dosperm mutants has revealed many genes related to starch synthesis, such as
GBSSI
(
waxy
) and
SSIIa
(
alk
). Recently we detected QTLs for eating quality, as evaluated by sensory testing of a cooked
rice experimental population derived from a cross between
japonica
rice cultivars. Fine-mapping of
these QTLs and gene isolation could reveal novel aspects of eating quality, since the QTLs were
not associated with differences in amylose or protein content. Further progress in research, such as
improvement of evaluation instruments and genetic dissection by means of novel reverse genetic
approaches, is still needed to explain and improve grain-quality traits in
japonica
rice cultivars.
ically classified based on morphological traits
including seed shape, grain shattering, and plant
architecture (Kato et al. 1928; Matsuo 1952), and
were recently classified by using whole-genome
DNA polymorphism analysis (Kovach et al.
2009; Ebana et al. 2010; Famoso et al. 2011).
Indica
rice is produced worldwide and is more
Introduction
Rice (
Oryza sativa
L.) is the most important food
crop in the world, as it is a staple food for more
than half of the world's population. Rice cultivars
are divided into two major subspecies:
indica
and
japonica
. The two subspecies have been histor-
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