Stresses‎ > ‎

Salinity

  • The problem:
    Salt stress (both salinity and alkalinity/sodicity) is a worsening problem in inland areas in SSA such as in Mali, Ethiopia, and Burundi because of the buildup of salt as a consequence of the excessive use of irrigation water with improper drainage, coupled with the use of poor-quality irrigation water or sodic soils developed from salt-bearing rocks. Over 20 million hectares of land suited to rice production in Asia are currently either underexploited or unexploited because of excess salt and other related soil problems, and in India and Bangladesh alone, productivity of more than 7 million hectares of rice land is adversely affected by salt stress. Salt-affected areas are predominantly inhabited by impoverished communities with fewer opportunities for food security and livelihood options. Rice is suitable for rehabilitating these soils because of its ability to grow under flooding and its high potential for genetic improvement. Rice productivity in salt-affected areas is very low, <1.5 t/ha, but can reasonably be raised by at least 2 t/ha (Ponnamperuma 1994), providing food for more than 10 million of the poorest people living off these lands. Salt-tolerant rice varieties also offer great potential to grow rice in marginal lands, which are usually left fallow particularly during the dry season because of high salinity. The area under this type of land is quite substantial—approximately 0.83 million hectares in Bangladesh and over 6.7 million ha in India. In West Africa, an estimated 1.5 million hectares of cultivable mangrove swamps are affected by salinity (Jones 1986).

  • Objective: The project aims to identify donors of superior tolerance mechanisms, and develop and use DNA markers to combine underlying QTLs/genes into varieties and breeding lines adapted to target areas.


Salt-Tolerant Rice

Mapping studies identified QTLs associated with salinity tolerance in rice. A major QTL, designated Saltol (mapped on chromosome 1 and explaining most of the variation in salt uptake), was recently fine-mapped and a marker-assisted backcrossing (MAB) system is being developed for its incorporation into popular varieties. Additional QTLs with relatively large effects were also mapped on other chromosomes and at least two of them will be targeted for fine-mapping and development of a MAB system for their pyramiding with Saltol for higher tolerance. Mapping populations are also being developed to identify QTLs associated with tolerance during the reproductive stage.

Similarly, multiple abiotic stresses often coexist in farmers’ fields, which require the incorporation of several QTLs and genes for tolerance. Examples are salinity and submergence in coastal areas and iron toxicity and salinity in most acid soils. The project’s next steps involve pyramiding QTLs with multiple tolerance in the same recurrent parents to develop more resilient varieties for wider adaptation. To ensure that the products of these efforts meet farmers’ needs, material developed through this project will be packaged with the best management strategies for salt-affected soils, and evaluated with farmer participation in target areas in Asia and Africa.

Salt-tolerant rice varieties released 


Research progress 

Refine phenotyping of rice breeding lines for salinity tolerance
Phenotyping of rice breeding lines for seedling-stage salinity tolerance has been made more stringent to avoid selecting intolerant lines. Rice breeding lines were screened in comparison with tolerant (FL478) and sensitive (IR29) checks on the 1–9 scale of the standard evaluation system (SES) of IRRI. NARES institutions such as the Central Rice Research Institute (CRRI), India, and Bangladesh Rice Research Institute (BRRI), Bangladesh, also developed their screening systems, for both the seedling and reproductive stages, using the protocol of IRRI but under ambient conditions. The Central Soil Salinity Research Institute (CSSRI), Karnal, has developed a new facility for evaluating rice genotypes for salinity tolerance up to the adult plant stage while CRRI is doubling its capacity for seedling- and reproductive-stage screening by constructing additional concrete screening tanks. Salt-tolerance screening at AfricaRice has been standardized with the IRRI approach, notably through the introduction of a rapid screening method at the seedling stage in the screenhouse. Furthermore, the salinity in on-station trials has increased from 3.5 to 6 dS m–1 and similar tolerant (Pokkali, Nona Bokra, I Kong Pao) and sensitive (IR29, IR31785) checks were included in the set for screening. Some 200 entries were screened under these conditions at Ndiaye, Senegal, and postharvest operations are under way.



List of PVS network sites, suitable germplasm, and management packages for each selected NARES site

Five key sites in India and two in Bangladesh were established for the large-scale testing of salinity-tolerant rice varieties and advanced breeding lines, along with appropriate management practices under participatory varietal selection (PVS). Within each site, a number of locations and villages as well as farmers within villages were selected for trials in 2008. Focus group discussions (FGDs) and baseline surveys have been conducted at nine sites in India and at two sites in Bangladesh. NARES partners from Rajendra Agricultural University (RAU)-Patna, Assam Agricultural University (AAU)-Assam, Mau and Ballia-NEFORD sites, Rice Research Station (RRS)-Chinsurah, CRRI, and CSSRI-Canningtown, India, have submitted some of the completely filled-out survey forms to IRRI headquarters.




Crosses made among genotypes differing for predominant physiological and biochemical mechanisms responsible for salinity tolerance and improved lines advanced to PVS trials 

Seventy-four single crosses and 257 backcrosses and multiple crosses were made during the 2008 dry season (DS) involving contrasting parents (Na excluder, high K uptake, tissue-tolerant, high initial vigor) and donors in various combinations to develop superior genotypes for salinity tolerance and Fe-toxicity tolerance. An additional 243 single and double crosses involving diverse donor parents were successfully made during the 2008 wet season (WS). Ten lines (varieties/breeding lines) at CSSRI-RRS, Lucknow; 10 at Narendra Deva University of Agriculture and Technology (NDUAT), Faizabad; 16 at CRRI, Cuttack; 13 at CSSRI-RRS, Canningtown; and 8 at BRRI and 10 at BINA, Bangladesh, were included in the researcher-managed PVS trials in the 2008 wet season.

Developing salt-tolerant varieties by marker-assisted backcrossing

MAB target: Pokkali allele at Saltol QTL on chromosome 1
Goal: to use MAB to rapidly transfer seedling-stage salt tolerance to popular varieties

Strategies for released varieties

Buildup of network of partners for out-scaling of seed production, demonstration, and adoption 
Up-scaling of quality seed production (BS/FS/CS/TLS)
Creation of awareness and demand for seed of stress-tolerant varieties
Development of effective and efficient mode of diffusion of seed from producer to farmers
Capacity building in quality seed production and preservation



Strategies for promising lines 

Simultaneous evaluation and pre-release awareness, generation, and seed multiplication
Policy intervention for fast-track release of MAS-generated lines, particularly in background of mega-varieties 
Quality seed production and rapid diffusion to stress-prone areas