Population Structure of a Worldwide Collection of Tropical Rice Indicates Limited Geographic Differentiation and Shows Promising Genetic Variability Associated with New Plant Type.

Abating the approaching yield plateau in rice requires taking advantage of potential technologies that requires knowledge on genetic diversity. Hybrid breeding, particularly in rice, requires the recruitment of large genetic variability from outside because the available genetic diversity of the cultivated pool has already been utilized to a great extent. In this study, we examined an assembly of 200 tropical lines collected worldwide for population genetic structure and variability in yield-associated traits. Tested along with 30 and six wild rice lines belonging to India, the tropical lines indicated great phenotypic variability, particularly related to new plant type (NPT) phenology, and formed six clusters. Furthermore, a marker-based characterization using a universal diversity marker panel classified the genotype assembly into four clusters, of which three encompassed tropical lines, while the last cluster included mostly lines. The population structure of the panel also revealed a similar pattern, with tropical lines forming three subpopulations. Remarkable variation in the allelic distribution was observed between the subpopulations. Superimposing the geographical sources of the genotypes over the population structure did not reveal any pattern. The genotypes sourced closer to the center of origin of rice showed relatively little diversity compared with the ones obtained from other parts of the world, suggesting migration from a common region of origin. The tropical lines can be a great source of parental diversification for hybrid development after confirming the presence of widely compatible genes.