The analysis of variation in cultivated plants with special reference to introgression

Abstract

That introgressive hybridization played an important role in the origins and further development of cultivated plants is a likely hypothesis, yet at present we need to gather new kinds of evidence by analysis and experiment. Three likely directions are suggested. (1) The study of the origins of cultivated ornamentals. Some ornamental plants are among our oldest domesticates; others have been domesticated within the last century. These latter are valuable material on which to determine the steps in domestication and the resulting changes in the germplasms. As an example well worth further study, the Louisiana irises are now well established as a group of cultivated varieties. Introgression in disturbed habitats under the impact of man produced recombinants of more than local interest. This stimulated further collection and controlled breeding. (2) Analysis of variation. Analysis of variation complexes (by means of metroglyphs) in variable populations give critical data on domestication. This is illustrated in detail for a variable semi-wild population of coffee in Ethiopia, readily resolvable into two introgressing complexes. (3) Field variability studies in the small grains. Our present understanding of variation patterns in the small grains is based upon individual specimens collected here and there from varying populations. Particularly near their centers of variability, we need to have scrupulously careful studies of a few populations from which such samples were drawn. The durum wheat fields in Ethiopia, as an example, are shown to consist of mixtures of bread and durum wheats, frequently including barley and sometimes lesser millets. They are sown as mixtures, reaped as mixtures, brewed and baked as mixtures. In fields of such complexity, opportunities for introgression are greatly increased. We should perhaps be thinking about the origin of the small grains as a group.