Genetic diversity and population structure in a world collection of Brassica napus accessions with emphasis on South Korea, Japan, and Pakistan

Information on genetic diversity and population structure is needed for continued improvement in Brassica napus L. A total of 169 B. napus lines, collected between 1970 and 2000 in Australia, Canada, China, Europe, Japan, Pakistan, and South Korea, were genotyped with 84 simple sequence repeat markers. Nei's unbiased genetic diversity (H) and Shannon's information index (SI) showed that genetic diversity was highest among lines from Europe followed by South Korea, Japan, China, and Pakistan while lines from Australia and Canada had the lowest diversity. Pairwise comparison of the populations using Nei's genetic identity (I) and genetic distance (D) showed greater differentiation between Australia and Canada versus China and Pakistan. Accessions from South Korea and Japan were most similar, confirming an historical exchange of germplasm. The analysis of unique alleles and allele richness revealed that the Pakistani population was the richest followed by Europe and South Korea. Analysis of molecular variance revealed that 9% of the variation was accounted for by geographical region and 91% by lines. Both Structure and principal coordinate analyses indicated two subpopulations in the collection confirming separation of genotypes due to growth habit adaptation. Information on B. napus genotypes containing unique alleles is valuable for breeding programs in different parts of the world seeking to improve agronomic traits and adaptability. © Crop Science Society of America.