A Different Saline Solution

Rice farmers on 1 million hectares of salt-affected coastal areas of Bangladesh stand to benefit from new cultivars bred with Saltol.

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 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.

Salt tolerant varieties compared to non-tolerant varieties

"Nearly 1 million hectares of the Bangladesh coast are affected by varying degrees of salinity," reports Dr. Zeba Islam Seraj, a professor of biochemistry and molecular biology at the University of Dhaka.

Seraj is a co-principal investigator of a project in the Generation Challenge Programme 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 (BRRI) with the gene Saltol, short for "salt tolerance."

Bangladesh Minister of Agriculture is shown varieties by IRRI scientists.

Using efficient marker-assisted selection, the International Rice Research Institute (IRRI) and its collaborators in the 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 the monsoon rains have washed the salt from the soil," explains Dr. Abdelbagi Ismail, the IRRI senior plant physiologist who is the principal investigator of the project.

Rice is susceptible to salinity at the seedling stage and again from a few days before panicle initiation until flowering and pollination. As Ismail explains, seedling salt tolerance is sufficient for the crop grown in the monsoon season, known as aman, provided that 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 in many areas to grow a second boro (dry) season irrigated crop. As the boro season coincides with high river water salinity, the rice must tolerate not only moderate salinity during its seedling stage but also much worse salinity during its second susceptible stage. 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 project aims to breed Saltol into at least one aman variety and one boro variety, thereby producing improved varieties that are identical to popular farmers' varieties in every way except that they have the Saltol gene and so are productive under moderate to high salinity. As Dr. M. Abdus Salam, the chief scientific officer and head of BRRI's Plant Breeding Division, makes the crosses and backcrosses to advance the breeding material, Seraj collects leaf samples for testing with newly developed molecular markers (easily detectable stretches of DNA) for both Saltol and the popular variety background. Based on the results, she advises Salam and the BRRI team on which plants to use in further crosses.

Salam is the site coordinator for a sister project led by Ismail under the Challenge Program for Water and Food (CPWF), which 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 saline 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."

It is no coincidence that Salam - who was the 2006 recipient of IRRI's Senadhira Rice Research Award - will handle, through farmer participatory varietal selection, the final testing of Generation's Saltol varieties in 2008.

"The two projects actually work closely together to maximize the benefits," explains Ismail. "The molecular markers for Saltol 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."