- The problem: Flooding afflicts some 20 million hectares in Asia. And as much as one-third of the rainfed lowland areas in sub-Saharan Africa are thought to be affected by submergence. Submergence stress is estimated to cause annual losses of up to $1 billion in Asia. Modern rice varieties are not adapted to these conditionsfarmers suffer from either regular yield loss when they grow these varieties or low yield when they continue to cultivate local landraces.
- The objective: Identify the best sources of tolerance, elucidate the genetic control mechanism behind it, and develop and test improved submergence-tolerant varieties under farmers’ and improved management practices.
Promising breeding lines
| IR70213-10-CPA 4-1-1-1
||Submergence-tolerant (SUB1) and adapted to stagnant flooding
||Tolerant of both submergence (SUB1) and anaerobic germination
| IRRI 119
||Tolerant of submergence (SUB1) and stagnant flooding
||Very good submergence tolerance (SUB1+) and tolerance for stagnating water
| IR07F287 (Samba Mahsuri-Sub1)
||Good grain quality and submergence tolerance
| IR07F290 (BR11-Sub1)
||Widely grown mega-variety of Bangladesh with SUB1 gene introduced|
Confirmation of donors of submergence tolerance that do not have the SUB1 gene
After repeated screening at IRRI, breeding lines and varieties with greater tolerance than the SUB1 near-isogenic lines (NILs) have been identified. These lines show higher survival and more rapid recovery after de-submergence. IR49830-7, the donor of SUB1 in many of the NILs, has the same tolerance as that of the original source variety, FR13A. It is presumed to have additional genes controlling submergence tolerance and has been used in crosses to develop varieties with higher tolerance. Some varieties that do not have the tolerant SUB1A allele by molecular marker analysis show moderate submergence tolerance. Screening will continue to identify new sources of tolerance that could potentially provide new genes that would increase tolerance level above that conferred by SUB1A.
Development of breeding lines that combine good agronomic and quality traits with tolerance for submergence during germination
Varieties with high tolerance for submergence during germination (anaerobic germination) were identified through previous screening of more than 8,000 rice varieties. Four of the best varieties (Khao Hlan On, Mazan Red, Khaiyan, and Cody) were crossed with improved breeding lines. Seven advanced lines were isolatedthese possess the same degree of tolerance as that of the tolerant parent and have good grain and plant type and high yield. These lines were extensively evaluated in the field in 2008.
Released submergence-tolerant varieties
Identification of participatory varietal selection (PVS) network sites, suitable germplasm, and management packages for each selected NARES site
Participatory varietal selection through the Africa Rice Breeding Task Force for at least 15 lines with submergence and/or stagnant flooding tolerance conducted in Sierra Leone, Mali, and Madagascar and at least 30% of the participants are women: Seven rice varieties from Asia (with/without SUB1) were distributed to NARES partners in Mali and Sierra Leone. The NARES evaluated the lines at three sites each along with their local checks.
Evaluate promising lines through yield trials in researcher-managed and farmer-managed PVS trials at six sites. At least 30% of the participants are women: Data for 2011 PVS trials were analyzed. A staff member also visited PVS sites in eastern India and monitored trials as well as collected data during the kharif season, and these data were
Establishment of facilities
Phenotyping facilities for short-term submergence and stagnant flooding established at AfricaRice, Ibadan: Two tanks with dimensions of 37 m × 17 m and 37 m × 18 m have been constructed at Ibadan and they can accommodate 1,000 entries for screening for tolerance of submergence and stagnant flooding each season.
Establish multilocation observational and yield trials at seven sites in India, two in Bangladesh, and one in Nepal: A set of observational yield trials (n = 80) for the 2011 wet season was planned during the annual STRASA planning meeting in India. This includes 10 IRRI entries. Advanced yield trials (n = 25) for shallow and semi-deep areas have also been prepared. In Bangladesh and Nepal, a set of observational trials has been planned, including 25 elite IRRI lines, and at least two trials will be carried out in each country.