Recent studies at IRRI have shown that some hybrid rice lines perform well under drought stress. Elite hybrids with improved drought tolerance are being identified. Although improving grain yield under drought stress is the key to alleviating poverty in drought-prone environments, varieties incorporating “packages of traits” for maximum performance in the target environment hold the greatest potential. Elite drought-tolerant breeding lines are being tested for resistance to the prevalent diseases (blast and brown spot) and acceptable grain quality to identify the most promising lines for these harsh environments. Promising drought-tolerant breeding lines are also being tested under typical crop management constraints caused by drought such as delayed transplanting and beushening
(a farmers’ weed management strategy). In line with this, flexible crop management recommendations will be developed to accompany any new varieties released.
- The problem: Drought regularly affects 23 million ha of rainfed rice in South and Southeast Asia. In the eastern Indian states of Jharkhand, Orissa, and Chattisgarh alone, rice production losses during severe droughts (about one in five years) average about 40% of total production, with an estimated value of US$800 million. Drought is considered a major constraint in both upland and rainfed lowland rice production in South and Southeast Asia, and the presence of drought tolerance in African rice Oryza glaberrima was an important objective for developing new varieties.
- Objective: Identify the best sources of tolerance, elucidate the genetic control, and develop and test improved drought-tolerant varieties under farmers’ field and improved management practices.
Standardized drought-screening protocols established at 10 sites in South Asia (India, Bangladesh, and Nepal)
A total of 17 sites were selected for field-managed drought screening in India (i.e., eight for rainfed lowland and nine for upland), in addition to two experimental stations each in Nepal and Bangladesh for drought screening under rainfed lowland conditions. Wet-season drought-screening trials have been conducted, following a standardized drought-screening protocol, at all 21 sites across India, Bangladesh, and Nepal. Field-monitoring tours were conducted in October 2008 in the three countries to examine field trials and fine-tune the drought-screening procedures. Climate and hydrological data were obtained for detailed characterization of the screening sites, and seasonal climate data will be collected together with the results of the drought-screening trials. A training course was conducted in India, with representatives from all participating centers (10-15 November 2008), on drought-screening protocols.
* The official release/notification date by the government of Nepal is on 15 May 2012, although these 3 varieties were officially recommended by the technical committee of government of Nepal in 2011
Inventory of all germplasm previously screened at AfricaRice/IRRI completed (for the identification of drought-tolerant donors among O. glaberrima accessions and other germplasm)
In Africa, a list of rice lines screened for drought tolerance from 2005 to date, in collaboration with projects supported by the Rockefeller Foundation and Generation Challenge Program (GCP), was made. These include O. sativa, O. glaberrima, and interspecifics. In South Asia, a list of germplasm screened for drought at IRRI since 2006 was compiled and integrated into the International Rice Information System (IRIS) database (www.iris.irri.org). Additional data, including potential drought-tolerant donors, all breeding lines screened in India over the past 3 years, and those screened at IRRI before 2005, are being integrated in the new drought database.
Improved breeding lines developed for drought-prone conditions in sub-Saharan Africa and South Asian target environments
At the Africa Rice Center (AfricaRice, formerly WARDA), some 804 newly fixed lines have been developed for drought tolerance from interspecific topcrosses using as parents O. sativa varieties (WAB56-104, Morobérékan, and WAB638) and O. glaberrima accession CG14. Seeds of 18 fixed interspecific lines from Caiapo/IRGC103544 for rainfed uplands and IR64/TOG5681 for rainfed lowlands are also being multiplied. In South Asia, observation yield trials (OYT) (131 entries) and advanced varietal trials (AYT100-120) of 100−120-day duration (45 entries) materials and similar trials (AYTGT120) of greater than 120-day duration (23 entries) materials were sent to Bangladesh and Nepal in 2008. A drought-tolerant breeding line from IRRI, IR74371-70-1-1 (IR55419-04*2/Way Rarem), was identified for release as a variety by India’s Central Variety Release Committee (CVRC) for the states of Orissa, Madhya Pradesh, and Tamil Nadu and it is likely to be released very soon by the State Varietal Release Committee (SVRC) of Jharkhand, where it has already been tested on a large scale in on-farm participatory varietal selection trials.
Marker-assisted breeding initiated for major drought-tolerance QTLs
A large-effect QTL (qtl12.1) for grain yield under drought located on chromosome 12 was tested in multilocation trials, and was characterized physiologically. This locus is now mapped to a distance of 1 million bp (about 3 cM) in the region spanning 16.5−17.5 million bp on chromosome 12. The relative effect of this QTL on grain yield is higher under increasing intensity of drought stress—from having no effect under well-watered conditions to having an additive effect of more than 40% of the trial mean under severe drought stress. Additional QTLs governing grain yield under drought in the lowland ecosystem have been identified in the population Apo/Swarna. Marker RM520 on chromosome 3 showed a large effect on grain yield under severe lowland drought stress and explained about 50% of the genetic variance of the trait. This QTL was also effective in yield improvement under mild stress in upland conditions and under mild and severe stress in lowland conditions. Marker-assisted selection has begun for introgression of this QTL in Swarna.
A drought-tolerant line performing well in Raipur, India
Participatory varietal selection (PVS) for at least 20 drought-tolerant lines at six key sites in South Asian target environments
PVS trials were conducted at six sites in India, at three sites in Nepal, and at one site in Bangladesh. At each site, PVS was conducted at two on-farm locations and one on-station location, resulting in a total of 30 PVS trials in the target region. From 10 to 20 entries were tested at each location and the entry list was country-specific. At each location, 30 to 150 farmers participated in the germplasm evaluation. Apart from PVS data collection, basic location characteristics and agronomic parameters for all entries were recorded. In addition to the PVS trials, two agronomic trials for evaluating the new germplasm under site-specific management constraints (e.g., low to medium nutrient availability, late transplanting, direct seeding) were conducted on-station at nine sites. The harvest of all trials was completed but sample analysis and data entry are still going on.
PVS in Raipur, India
NILs and breeding lines for drought tolerance
Near-isogenic lines (NILs) developed for IR64/Adaysel (RM 511) QTLs
- NIL development for RM520, RM17435, and RM510 under way
- Advanced breeding lines with IR64/Adaysel, RM520, and RM511 QTLs under evaluation in national programs
- For upland: efforts under way to combine QTLs (RM6703, RM256) in Apo background and RM122 and RM17435 in IR55419-04 background
A drought-tolerant line at Raipur, India
Promising drought-tolerant entries in PVS: Raipur, 2008 wet season