Genetic diversity of soybean cultivars from China, Japan, North America, and North American ancestral lines determined by amplified fragment length polymorphism

Asian soybean [Glycine mar (L.) Merr.] improvement programs have been conducted for many years almost completely independent of U.S. breeding programs. Productive, modem Asian cultivars may be a promising source of new yield genes for U.S. breeding programs. However, this hypothesis has not been tested. The objectives of this study were to determine the level of genetic diversity within and between Asian and North American soybean cultivars (NASC) by amplified fragment length polymorphism (AFLP) analysis and to identify Asian cultivars with significant genetic difference from NASC. The genetic diversity and relationships were assessed among 35 North American soybean ancestors (NASA), 66 high yielding NASC, 59 modern Chinese cultivars, and 30 modern Japanese cultivars. Five AFLP primer-pairs produced 90 polymorphic (27%) and 242 monomorphic AFLP fragments. Polymorphic information content (PIC) scores ranged from zero to 0.50. Only 53 of the 332 AFLP fragments provided PIC scores :0.30. Genetic distance (GD) between pairs of genotypes was calculated on the basis of the similarity indices determined by the 332 AFLP fragments. Within each of the cultivar groups' the average GD between pairs of genotypes was 6.3% among the Japanese cultivars, 7.1% among the NASC, 7.3% among the NASA, and 7.5% among the Chinese cultivars. The average GD between the NASC and the Chinese cultivars was 8.5% and between the NASC and the Japanese cultivars was 8.9%. Although these distances were not significantly different, they were greater than the average GD between all pairs of NASC (7.1%). Clustering and principal coordinate analysis using all 332 fragments showed a separation of the cultivars into three major groups according to their geographic origin. North American soybean ancestors overlapped with all three cultivar groups. The Japanese cultivars were more removed from NASA and NASC than the Chinese cultivars and may constitute a genetically distinct source of useful genes for yield improvement of NASC.