The Influence of Breeding Habit on the Outcome of Natural Hybridization in Plants

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Abstract
Where the time available for reproduction by a natural hybrid is critical, as it is in annual herbs, biennials, and short-lived perennials, the natural hybridization will tend to run toward polyploidy under conditions of self-fertilization and toward introgression under conditions of out-crossing. We accordingly find in some annual and biennial groups, where hybridization has occurred on an extensive scale, that polyploidy is closely associated with autogamy and introgression with outcrossing. In long-lived perennial plants these tendencies may be obscured and reversed by other factors. The association of allopolyploidy with an outcrossing breeding system, which was noted by Gustafsson (1947), is found chiefly in plants with a perennial habit and/or vegetative means of propagation.