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Seasoned for Salt
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Salt makes its way into the rice paddies of coastal Bangladesh
every which way. During the dry season, when the flow of freshwater
out to the mouths of the Ganges is weakest, saltwater rides inland
on the tide, and saline groundwater rises and spreads laterally
across the delta. Salinity is less prevalent during the wet monsoon
but can still poison rice crops as it lingers in the soil,
percolates into paddies from the brackish ponds of neighboring
shrimp farmers and, during drought, rises as in the dry season.
"Nearly 1 million hectares of the Bangladesh coast are
affected by varying degrees of salinity," reports Zeba Islam
Seraj, a professor of biochemistry and molecular biology at the
University of Dhaka.
Seraj is a co-principal investigator of a project of the
Generation Challenge Programme (GCP) that aims to revitalize
marginal rice lands by discovering and breeding into popular rice
varieties genes for tolerating soils that are saline or deficient
in phosphorus. As the focal collaborator in Bangladesh, she is
responsible for the molecular evaluation and selection of rice
lines bred by the Bangladesh Rice Research Institute with which to
insert into popular farmers' cultivars the gene
Saltol, short for "salt tolerance."
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Faizabad (India) farmer Bismillah Khan
shows the rice he obtained from the salt-tolerant variety he grew
in an on-farm trial. His regular, nontolerant crop is in the field
in which he stands. The combination of salt stress and drought
meant he had to harvest his crop early and feed it to his cattle.
The good performance of the new varieties encouraged him to invest
in supplementary irrigation, which allows a good crop even under
the prevailing harsh conditions. (Photo: IRRI)
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Seraj is a co-principal investigator of a project of the
Generation Challenge Programme (GCP) that aims to revitalize
marginal rice lands by discovering and breeding into popular rice
varieties genes for tolerating soils that are saline or deficient
in phosphorus. As the focal collaborator in Bangladesh, she is
responsible for the molecular evaluation and selection of rice
lines bred by the Bangladesh Rice Research Institute with which to
insert into popular farmers' cultivars the gene
Saltol, short for "salt tolerance."
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Dr. Abdelbagi Ismail (right) shows former
Bangladeshi Minister of Agriculture M.K. Anwar (center) and IRRI
senior economist Mahabub
Hossain how researchers select for salt-tolerant rice plants in an
IRRI greenhouse. (Photo: IRRI)
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Using marker-assisted selection, which allows rapid screening of
large numbers of plants, the International Rice Research Institute
(IRRI) and its collaborators in the GCP project have mapped
Saltol - which accounts for 40-65% of the salt tolerance
observed - to a small segment of rice chromosome 1. Importantly,
Saltol and the other identified loci confer salinity
tolerance at the seedling stage.
"This is essential in the monsoon season, when salinity
tolerance is mainly needed during seedling transplantation and for
a few weeks thereafter, until rain has washed the salt from the
soil," explains Abdelbagi Ismail, the IRRI senior plant
physiologist who is the principal investigator of the GCP
project.
Rice is susceptible to salinity during two periods of
its growth cycle. The first is the seedling stage and the second
begins a few days before panicle initiation and ends with flowering
and pollination. As Ismail explains, salt tolerance at the seedling
stage is sufficient for the crop grown in the wet monsoon, known as
aman, provided there is no drought. This is the
traditional season for rice cultivation in Bangladesh, but the
spread of tube wells in recent years has allowed farmers to
irrigate and grow a second, boro (dry) season crop.
As the boro season coincides with high river water salinity,
rice grown in this season must tolerate not only moderate salinity
during the seedling stage but also much worse salinity during the
critical period from panicle initiation to the start of grain
filling. As food security and farmers' well-being in Bangladesh
depend increasingly on boro rice, rice varieties that yield well
under high salinity stress are needed more urgently than ever.
The GCP project aims to breed Saltol into at least one
aman variety and one boro variety already popular with farmers. The
goal is to develop improved varieties that are identical to popular
farmers' varieties in every way except that they have the
Saltol gene and so are able to provide a reasonably good
yield under conditions of moderate to high salinity in which salt
accounts for 0.4-0.5% of the soil.
A sister project led by Ismail under the Challenge Program for
Water and Food (CPWF) aims to harness the productivity potential of
salt-affected areas of three river basins, including the Ganges. In
that project, the partners use the newly developed lines that have
the Saltol locus and also search for additional sources of
salinity tolerance.
"Saltol and other genes conferring tolerance at
the seedling stage could be sufficient for the wet season,"
Ismail observes. "However, for the boro season, additional
genes for higher tolerance during flowering and pollination are
needed.
"The two projects actually work closely together to
maximize the benefits," Ismail adds. "The molecular
markers for Saltol developed through the GCP will help
speed the breeding progress of the CPWF project, and the material
will be further tested and scaled out through CPWF activities, as
well as other networks. Neither of the two projects could achieve
this without the other."
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