Submitted to: Proceedings of the OECD Conference on Biological Resources & Migration
Publication Type: Proceedings
Publication Acceptance Date: January 20, 2004
Publication Date: May 20, 2005
Citation: Carter Jr, T.E., Hymowitz, T.E., Nelson, R.L. 2004. Biogeography, local adaptation, vavilov, and genetic diversity in soybean. In D. Werner (ed):Proceedings of the OECD Conference on Biological Resources & Migration. p. 47-59. Interpretive Summary: Soybean landraces developed in Asia are irreplaceable agricultural genetic resources because they are the sum of genetic diversity that was amassed by farmers during the long transformation of soybean from wild plant to modern crop. These landraces were selected by the human eye for perceptual distinctiveness, traded north and south throughout Asia to allow further farmer selection for local adaptation, and formed a series of isolated gene pools to develop biogeographical genetic patterns in soybean which are present today. Many landraces were collected by plant explorers, germplasm curators, and breeders and are preserved today in extensive germplasm collections. These landraces serve as the basis for almost all modern improvements in soybean. Modern breeding expands the process of local adaptation initiated by ancient farmers in Asia to a global basis. The model for modern soybean breeding is hybridization of land races (and their derivatives), development of large numbers of progeny, and selection of those rare recombinant progeny which have beneficial characters from both parents. Many breeding successes have been achieved in this way. The legacy of genetic diversity resulting from the global spread of soybean has made these successes possible. Thus dispersal and adaptation to local conditions in the 20th century as well as in ancient times, is a part of soybean's genetic story.
Technical Abstract: It is the purpose of this paper to illustrate the impact of geography, climate, and humankind in shaping the present-day genetic diversity in soybean. Examination of soybean germplasm collections around the globe reveals that an enormous phenotypic range in genetic traits exists in soybean. The diversity in domesticated soybean is the result of 3000 years of cultivation in which Chinese farmers selected more than 20,000 landraces. The more recent spread of soybean out of Asia in the past 250 years, coupled with modern breeding efforts of the past 70, has increased the phenotypic range in soybean and this increase has a clear bio-geographical interpretation which relates to genetic alteration of photoperiod response, adaptation to latitude, and tolerance to climate extremes. It is important to note that global dispersal of soybean has NOT had a corresponding positive impact on genetic diversity in the modern breeding programs. DNA marker and pedigree analyses of diversity in modern cultivars indicate that diversity is greatest in cultivars developed in China, less in Japan and least North America. Phenotypic analysis of modern Chinese and North American cultivars follow the same pattern of diversity. Pedigree analyses of Latin American and Indian soybean breeding programs show that they are derived primarily from a subset of North American breeding stock and are less diverse than the North American breeding program. Although conscious breeding choices, economics, and historical factors can be used to explain the reduced diversity in breeding programs outside of China vs. within, these results are consistent with 1) Vavilov's principle of crop domestication which states that genetic diversity will be greatest at the center of domestication (China in the case of soybean), and 2) the concept of Darwinian genetic drift which can be used to infer that genetic relatedness or uniformity will increase within breeding populations that are derived from relatively few founding members. All soybean breeding programs outside China, regardless of the phenotypic superiority of their genetic breeding materials, should be examined to determine the adequacy of genetic diversity.