Tough grains
International
Rice Research Institute has adhered to precision plant breeding for
developing flood-resistant variety of rice. Times Food Processing Journal
reports
While
most modern rice varieties have superior characteristics like high yield
and good grain quality, few are tolerant of the abiotic stresses that
limit the productivity in unfavourable rain-fed areas, which are also
home to the world's poorest rice farmers. Conventional breeding has
produced some modern varieties with high yield and tolerance to stresses
such as flooding or drought. However, these varieties have generally
not been widely adopted due to other undesirable features. Put simply,
farmers expect all rice varieties now to have high yield, good quality
and some resistance to pest and disease – only then can breeders
add tolerance to abiotic stresses like flooding or drought. Anything
less will simply not be adopted by farmers.
A breakthrough
Fortunately, recent advances in gene mapping have identified QTLs for
abiotic stress tolerance that should allow for significant improvements
to most modern rice varieties. Before this, nearly all the breeding
work was done without an understanding of the underlying genetics. The
major QTL for submergence, Sub1 was only identified about 10 years ago.
A fine-scale map of the Sub1 QTL then provided a foundation for markerassisted
backcrossing to develop submergencetolerant versions of modern, higher
yielding varieties. A submergence-tolerant version of the popular South
Asian variety Swarna was then developed because it's already grown on
around six million hectares in India and Bangladesh. As the sequence
from the gene.
was available,
markers were also developed that could pinpoint the gene. The story
of the Sub1 gene is an example of how new scientific knowledge has greatly
accelerated progress in developing new varieties that offer farmers
a significant chance to improve rice productivity, despite environmental
challenges. This was confirmed by the recent discovery by scientists
from the International Rice Research Institute (IRRI) and the University
of California that submergence tolerance is conferred by the Sub1A gene,
one of three ethylene response factor genes at the Sub1 locus. However,
perhaps the most promising application of this breakthrough is the use
of the Sub1 sequence for allele mining of the gene bank to discover
new submergencetolerant genes. These genes are known to exist because
there are varieties with higher levels of tolerance than that can be
obtained from Sub1 alone. Being able to pyramid all these genes would
provide even more protection against floods. From a handful of the most
tolerant cultivars, IRRI researchers have already found some that do
not have the tolerant Sub1A allele and genetic analysis is underway.
The role of Sub1A and the other ERF genes is now being elucidated, which
should help identify other genes important for submergence tolerance.
The Swarna-Sub1 line is now under evaluation in India, Bangladesh and
Indonesia. At IRRI, it shows the same grain quality and yield potential
as the original parent under shallow conditions. Under submergence stress
of 12-18 days, IRRI researchers have noted a twofold to threefold yield
advantage, representing about 1-2 tonne of extra grain yield per hectare.
Preliminary field evaluations in target areas in India and Bangladesh
show similar results. While the Sub1A gene is not the answer to all
flooding problems, it will have wide applications and should be suitable
for incorporation into rice varieties grown in areas subject to frequent
submergence, estimated at around 15 million hectares.
Most excitingly,
it is not a phenomenon that is one-of-a-kind. The availability of the
complete genome sequence of rice and new molecular tools have provided
exiting new opportunities to finally overcome major problems in developing
world agriculture. IRRI is already taking advantage of gene discovery
research at advanced research institutions and applying it to the problems
faced by poor farmers. The opportunities have now shifted to the laboratory-field
interface where knowledge of germplasm, phenotyping skills and pathways
to delivery play an essential role. At this stage, IRRI is set to play
a crucial role in discovering and utilising genes that have the potential
to vastly improve the lives of the poor.
