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.
THE STRASA SOLUTION
Donor identification and line development
Breeding populations have been developed from new drought-tolerant O. glaberrima accessions, leading to the identification of progenies with good drought tolerance and high yield potential. Polymorphism has been detected between genomes of sister lines NERICA 3 (drought sensitive) and NERICA 4 (highly drought tolerant) in populations developed between the two, revealing 27 homozygous SNPs, 12 indels, and 13 validated SNPs so far (Figure at right). The IRRI ESA breeding team identified 15 accessions which showed consistent drought tolerance in Tanzania for two seasons in rainfed lowland trials. These could be new sources of drought tolerance.
Donor variety identification: The project screened 500 Aus and traditional varieties at IRRI for tolerance to seedling stage upland drought, reproductive stage upland drought, and reproductive stage lowland drought, together with resistance to blast and bacterial blight.
These trials were conducted during the dry seasons from 2014 to 2018. Each year, selected donor genotypes were sent to NARES partner sites for testing under a range of conditions. In 2018DS and 2019DS, the project trialed the 60 "Best Donors", identified from 2014 to 2017, at IRRI under reproductive stage drought with the mentioned tolerant traits.
These were also shared with CRURRS Hazaribagh for blast and bacterial blight evaluation in the 2018 Kharif season to compare the pathogen resistance of the drought donors in response to strains at IRRI with their response to strains in Jharkhand, India.
Throughout STRASA Phase 3, these Best Donors have been used in drought breeding programs in NARES partner sites, and are being used to develop new material for the trait development breeding pipeline for marginal environments at IRRI.
Head to head trial in a project site in India
A participatory varietal selection (PVS) in Institute of Agriculture and Animal Science (IAAS), Lamjung, Nepal
A field ready for harvest in Tripura, India
QTL identification: The project identified five consistent QTLs (qDTY1.1, qDTY2.3, qDTY3.3, qDTY6.3, and qDTY11.2) for grain yield under drought stress. Two BC1F3 mapping populations – Swarna*2/Dular and IR11N121*2/Aus 196 – were phenotyped in 2016 and 2017 under reproductive stage drought stress and non-stress conditions. Genotyping was performed using the next generation sequencing (NGS)-based approach called genotyping by sequencing (GBS) using the DNA of these two mapping populations through MACROGEN, Korea. A total of 3,929 polymorphic SNP markers well distributed on all 12 chromosomes were identified from the GBS data of Swarna*2/Dular to identify the QTLs for reproductive stage drought tolerance.