Rice Genomics and Genetics 2015, Vol.6, No.9, 1-9
2
sufficiently stable across a wide range of growing
environments and (iii) traits for high nutrient content
can be combined with superior agronomic and high
yield characteristics (Welch and Graham, 2004).
Thousands of SSR markers have been mapped and
developed as molecular markers (McCouch et al
.
,
2002;
). The microsatellite markers
are supposed to be particularly suitable for
evaluating genetic diversity and relationships among
closely related plant accessions or individuals, such
as different rice cultivars. Markers linked to the gene
can be used to select plants possessing the desired
trait, and markers throughout the genome can be
used to select plants that are genetically similar to
the recurrent parent (background selection). This
approach is thought to be promising in rice because
a number of rice cultivars are widely grown for their
adaptation, stable performance, and desirable grain
quality.
Alternatively, genetic transformation can be used to
transfer useful genes in commercially important rice
varieties without disrupting their otherwise desirable
genetic make-up. The development of efficient
protocols for
in vitro
culture and transformation of
japonica
as well as
indica
rice varietieswere reported
(Jain 2003; Veluthambi et al., 2003).
1 Rice and Genetic diversity for mineral
content
Oryza
is an agronomically important genus containing
species with highly diverse morphology. The genus
Oryza
includes cultivated rice species,
O. sativa,
which constitutes an important part of the diet of
more than half of the world’s population. More than
90% of this cultivated rice is grown and consumed
in Asia. India stands first in terms of area under rice
cultivation and second in rice production after China.
Worldwide, rice production has more than doubled
in 35 year period from 257 million tons in 1996 to
600 million tons in 2000. Rice (
Oryza sativa
) has
become a model cereal for genomic research
because of its small genome size (~430 million bp)
and diploid nature. International Rice Research
Institute (IRRI, The Philippines) and national research
institutions in various countries are maintaining >
200,000 germplasm accessions of rice. Rice is one
of the most diverse crops being grown as far north as
Manchuria (China) and far south as Uruguay and
New South Wales in Australia. In the last twenty
years, a rapid progress has been made towards the
basic and applied research in rice biotechnology and
molecular biology. In fact, progress towards
development of molecular techniques has been more
rapid with rice than any other cereal. Some of the
milestones includes: (i) development of the first
saturated restriction fragment length polymorphism
(RFLP) map; (ii) the application of polymerase
chain reaction (PCR) based markers such as simple
sequence repeat (SSR) markers, amplified fragment
length polymorphism (AFLP); (iii) the identification
of genes/quantitative trait loci (QTLs) for many
agronomically important traits and marker assisted
breeding; (iv) development of efficient techniques
for genetic transformation; (v) complete sequencing
and annotation of
indica
and
japonica
rice; (vi)
Development of new generation markers (SSR, SNP,
InDel, etc) (Shen et al., 2004), (vii) synteny between
genomes of rice and other cereals (Xu et al., 2005)
and (viii) access to several genome databases that
facilitate depositing, searching, querying and
analyzing information about rice and other cereals
that
makes rice a good entry point for characterizing the
genes of other cereals, and associating them with
various agronomic traits.
Gregorio et al., (2000) reported wide range of Fe
(6.3~24.4 µg/g) and Zn (13.5~58.4 µg/g) concentrations
in brown rice within the eight sets of genotypes,
which clearly indicates existence of genetic potential
to increase the concentration of these micronutrients
in rice grain. Genetic component analysis conducted
for high-Fe trait in grain using four traditional
high-Fe rice varieties (Azucena, Basmati 370, Xua
Bue Nuo and Tong Lang Mo Mi), three advanced
lines (IR61608, PP2462-11 and AT5-15), and three
IRRI released varieties (IR36, IR64 and IR72)
showed significant genetic effect on grain Fe
concentration, suggesting that selection among F
1
progenies is possible. Fageria (2001) identified
several Zn-efficient rice genotypes, which had Zn
concentration of 20~25 ppm. Results so far obtained
from various micronutrient projects across the world
indicate that the breeding parameters are not difficult
and are highly likely to be low cost.
