Submitted to: Journal of Crop Improvement
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/8/2005
Publication Date: 11/1/2005
Citation: Sneller, C., Nelson, R.L., Carter Jr, T.E., Cui, Z. 2005. Genetic diversity in crop improvement: the soybean experience. Journal of Crop Improvement. Vol. 15, No. 1/2 (#27/28) pp. 103-144. Interpretive Summary: Soybean variety development is a long term effort. Over the past 50 years more than 300 public varieties have been developed in the US that have significantly raised yield level and have provided genetic resistance to many potentially devastating diseases. The general technology for these successes has been to identify good existing varieties, mate them and identify offspring that are better than either parent. This tried and true formula for success is running into problems, however. Recent studies show that soybean breeding is approaching a bottleneck in terms of yield improvement, especially under pest free conditions. The cause of the bottleneck is that varieties have become too closely related. For some regions of the US, the best soybean varieties are as closely related as brother and sister. These genetic similarities are too great to expect that their mating will produce desirable new varieties for farmers. Thus, breeding progress may come to a halt unless steps are taken. The ideal solution is to identify and bring new breeding stock into US breeding programs. The best breeding stock outside the US is found in Japan and China. Dr. Carter has been involved for some time in identifying, locating and using this Asian breeding stock. Dr. Carter's approach is unique in that he has been collaborating with Japanese scientists to help identify breeding stock that most benefit US farmers. This paper describes breeding patterns in Japanese varieties based on pedigree.
Technical Abstract: Crop diversity is essential to sustainable food production. Japan is a historical center of diversity for soybean (possibly introduced ca. 0 A.D.) but diversity of modern Japanese cultivars is not well characterized. The objectives of this study were to quantify genetic diversity of Japanese cultivars via coefficient of parentage (CP) analysis, to determine the relative importance of breeding factors in explaining that diversity, and to incorporate results into a practical guide for management of diversity. Eighty-six publicly released Japanese cultivars were subjected to CP and multivariate analysis for this purpose. The mean CP for the 86 cultivars was low (0.04), with eighty percent of all pairs of cultivars completely unrelated. These results indicated a potentially high degree of diversity in Japanese breeding. Despite the low mean CP value for Japanese cultivars, diversity patterns were evident in the Japanese pedigrees; and, cluster analysis was an effective discriminator of those patterns. Clusters encompassed a total of 54 cultivars, explained 57% of the variation in the CP relations, and had almost no pedigree in common with each other. The low mean CP for the Japanese cultivars was attributed to a continual incorporation of unique Japanese land races into the genetic base over time, and to the introduction of foreign germplasm from China and the US-CAN as breeding stock. We suggest that breeders may maximize their chances of finding good specific US-CAN by Japanese or Chinese by Japanese cultivar crosses through i) sampling a wide array of Japanese cultivar clusters rather than sampling extensively within a cluster, ii) avoiding Japanese cultivars with U.S. or Chinese pedigree, and iii) selecting cultivars with desirable phenotype such as high yield.