IRRI’s drought stress research in rice with emphasis on roots: accomplishments over the last 50 years

Early recognition of the importance of roots for drought resistance, and the diversity in rice root architecture, provided a strong foundation for drought research at the International Rice Research Institute (IRRI). IRRI was founded in 1960, and large efforts for research on root growth in response to drought were ongoing by the mid-1970s, with an emphasis on deep root growth, formation of coarse nodal roots, and the root pulling force method. In the 1980s, aeroponic studies on root morphology and anatomy and line-source sprinkler field studies were commonly conducted. The use of crosses to better understand the genetics of root traits started in the 1980s. Further characterization of the genetics behind root traits was conducted in the 1990s, specifically the use of molecular markers to select for root trait QTLs. A shift toward rainfed lowland experiments in addition to upland conditions began in the 1990s, with increased recognition of the different types of drought stress environments and characterization of root water uptake. In the 2000s, drought breeding efforts moved from selection of root traits to direct selection for yield under drought. Today (the 2010s), we have identified two major drought-yield QTLs to be related to root traits, and phenotyping for association mapping of genes related to root traits and functions is underway. After direct selection for yield during the past decade that is now approaching impact at the farm level, we are seeing that root traits are indeed involved in improved yield under drought.