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
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