Genetic Diversity of Soybean Cultivars from China, Japan, North America, and North American Ancestral Lines Determined by Amplified Fragment Length Polymorphism

level that could limit continued breeding success. Introduction of new sources of germplasm into the breeding Asian soybean [Glycine max (L.) Merr.] improvement programs pool may provide the genetic variability to permit conhave been conducted for many years almost completely independent of U.S. breeding programs. Productive, modern Asian cultivars may tinued progress in developing high yielding cultivars. be a promising source of new yield genes for U.S. breeding programs. Though plant introductions (PIs) provide genetic variHowever, this hypothesis has not been tested. The objectives of this ability, they are less frequently used as sources of new study were to determine the level of genetic diversity within and yield genes than current cultivars and elite lines because between Asian and North American soybean cultivars (NASC) by they often yield less. Populations developed from crossamplified fragment length polymorphism (AFLP) analysis and to ing cultivars with PIs, which have been selected for good identify Asian cultivars with significant genetic difference from NASC. phenotypic traits, generally have a lower mean yield The genetic diversity and relationships were assessed among 35 North and lower frequency of desirable lines than those popuAmerican soybean ancestors (NASA), 66 high yielding NASC, 59 lations developed from crossing elite parents (Vello et modern Chinese cultivars, and 30 modern Japanese cultivars. Five al., 1984; Ininda et al., 1996). Recent studies have used AFLP primer-pairs produced 90 polymorphic (27%) and 242 monomorphic AFLP fragments. Polymorphic information content (PIC) molecular markers to help identify genetically diverse scores ranged from zero to 0.50. Only 53 of the 332 AFLP fragments PIs to use in crosses in cultivar improvement programs provided PIC scores 0.30. Genetic distance (GD) between pairs (Thompson and Nelson, 1998a,b; Thompson et al., 1998; of genotypes was calculated on the basis of the similarity indices Narvel et al., 2000). These studies have had more success determined by the 332 AFLP fragments. Within each of the cultivar than conventional selection programs in producing progroups, the average GD between pairs of genotypes was 6.3% among ductive lines from PI crosses with elite genotypes. Modern the Japanese cultivars, 7.1% among the NASC, 7.3% among the Asian cultivars, which share no ancestors with NASC, NASA, and 7.5% among the Chinese cultivars. The average GD represent a potential reservoir of new alleles available between the NASC and the Chinese cultivars was 8.5% and between for improving U.S. soybean yield, and is a different apthe NASC and the Japanese cultivars was 8.9%. Although these proach than using other germplasm in crosses with distances were not significantly different, they were greater than the average GD between all pairs of NASC (7.1%). Clustering and princiNASC. pal coordinate analysis using all 332 fragments showed a separation Acquisition of soybean germplasm from Asia has inof the cultivars into three major groups according to their geographic creased over time, though not all the introduced cultiorigin. North American soybean ancestors overlapped with all three vars or germplasm have been assessed for their usecultivar groups. The Japanese cultivars were more removed from NASA fulness in soybean improvement. There is a need for and NASC than the Chinese cultivars and may constitute a genetically extensive evaluation of new germplasm from Asia to distinct source of useful genes for yield improvement of NASC. determine its genetic diversity and to identify Asian lines to serve as sources of unique genes for U.S. soybean yield improvement. S is one of the world’s most important oil Conventional molecular marker analysis using restricand protein crops. By selection and hybridization, tion fragment length polymorphism (RFLP) (Apuya et breeders in the USA have increased soybean yield by al., 1988), ribosomal DNA (Doyle and Beachy, 1985), at least 20% (Fehr, 1984). More than 300 publicly develand random amplified polymorphic DNAs (RAPDs) oped cultivars have been released in North America in (Williams et al., 1990) have identified only low levels the past 50 yr (Thompson and Nelson, 1998b). However, of genetic diversity in cultivated soybean. Microsatellite it has been observed that the use of only a few plant markers can detect higher levels of genetic diversity introductions and intensive plant breeding have naramong soybean cultivars but this marker system rerowed the genetic diversity among North American elite quires the synthesis of primers and construction of genosoybean cultivars (Gizlice et al., 1994; Sneller, 1994). mic libraries (Maughan et al., 1996). AFLP is a PCRThe genetic similarity among NASC has reached a based, molecular technique that detects high numbers of polymorphic bands (Powell et al., 1996). AFLPs are G.N. Ude, W.J. Kenworthy, and J.M. Costa, Dep. of Natural Resource detected frequently in soybean, are inherited in a stable Sciences and Landscape Architecture, Univ. of Maryland, College Mendelian fashion, and exhibit high levels of diversity Park, MD 20742; P.B. Cregan, USDA-ARS, Soybean Genomics and Improvement Lab., Beltsville, MD 20705; J. Alvernaz, Dep. of Crop (Maughan et al., 1996). The objectives of this study were and Soil Sciences, Univ. of Georgia, Athens, GA 30602. This research to determine the level of genetic diversity within and was supported in part by a grant from the United Soybean Board. between Asian and NASC by AFLP analysis and to The research was part of a dissertation submitted by the senior author in partial fulfillment of the Ph.D. degree. Received 5 Feb. 2002. *CorAbbreviations: AFLP, amplified fragment length polymorphism; GD, responding author ([email protected]). genetic distance; NASA, North American soybean ancestors; NASC, North American soybean cultivars; PIC, polymorphic information Published in Crop Sci. 43:1858–1867 (2003).  Crop Science Society of America content; RAPD, random amplified polymorphic DNA; RFLP, restriction fragment length polymorphism. 677 S. Segoe Rd., Madison, WI 53711 USA