15 Reading 3-1 the methods are time consuming and expensive, compared to some of the other techniques. Discussion and references may be found in Brown et al. (ed.), Plant Population Genetics, Breeding and Genetic Resources (1990). No modern study of diversity has con f rmed the intuitive geographic patterns described by Vavilov. Some concentrations of diversity can be detected, to be sure, but they have little or nothing to do with origins. For example, Peeters (1988) used the Cambridge barley collection, recording 12 qualitative and 18 quantitative traits averaged over 3 yr, for more than 100,000 observations and concluded the greatest diversity in barley is in USA, followed by Turkey, Japan, USSR, and China. Afghanistan is 16th and Ethiopia 18th. There was no real center with geographic integrity. Other studies have given similar anomalous results. Vavilov had to concede that his method of “differential phytogeography” did not work very well. He invented the concept of secondary centers to account for the fact that centers of diversity are not the same as centers of origin. In fact, the variation in secondary centers is often much greater than in the centers of actual domestication where these can be located on independent evidence. He also developed the concept of
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