SNP Variation in Donor Germplasm Used in National Rice Breeding Programs.

The continuous use of few and genetically related parents in breeding contributes to the narrowing of the genetic base of modern varieties. In rice, to expedite the evaluation and utilization of genetic diversity in varietal improvement, the International Network for Genetic Evaluation of Rice (INGER; http://seeds.irri.org/inger/), established in 1975, has distributed thousands of unique breeding lines to over 80 countries in the past three decades. Hundreds of varieties have been developed and released from the more than 17,000 crosses made involving INGER entries as parents. This study aimed at determining the extent of genetic variation among INGER entries utilized as parents in rice breeding programs. Forty-five of the most popular genotypes utilized as genetic donors in 14 countries and 20 reference varieties were assayed using 377 SNP (single nucleotide polymorphism) markers. Genetic distances were computed based on CS Chord and clustering was based on UPGMA (unweighted pair group method with arithmetic mean) using Power Marker V3.25. Four distinct clusters were observed and genetic distances within groups ranged from 0.17 to 0.33. On the other hand, genetic distances between groups ranged from 0.27 to 0.56 (0.45 mean). Breeding lines utilized in a specific country were distributed in different groups. Thus, utilization of these genetic donors in different countries contributed to the maintenance and/or enhancement of genetic diversity in the different breeding programs.