These 20 diverse varieties and landraces were used for SNP discovery by tiling arrays. Resequencing microarrays were used to interrogate 100 Mb of the unique fraction of the reference genome that captured the impressive genotypic and phenotypic diversity of domesticated rice. Introgression patterns of shared SNPs revealed the breeding history and relationships among the 20 varieties; some introgressed regions are associated with agronomic traits that mark major milestones in rice improvement.

The study was done by Dr. Kenneth L. McNally, et al. in 2009 in https://www.pnas.org/content/early/2009/07/10/0900992106