Rapid phenotypic divergence of feral rye from domesticated cereal rye

Feral rye is an agricultural and ruderal weed of the western United States. We investigated how it has phenotypically diverged from its cultivated ancestor, domesticated cereal rye, and across its range since the introduction of its progenitor. Vegetative growth, flowering phenology, and reproductive characters of feral populations from across a 13 degrees range in latitude in the northwestern United States were compared to that of rye cultivars under both vernalized (cold-treated) and nonvernalized conditions. Feral populations as a whole had smaller seeds, thinner culms, and a delay in flowering relative to cultivars, regardless of cold treatment. Vernalized feral populations from northern latitudes (northern California and eastern Washington) produced more, but smaller leaves and more tillers than both vernalized rye cultivars and southern California feral populations. Northern feral populations also flowered significantly later, irrespective of vernalization treatment. We conclude that feral rye is phenotypically distinct from domesticated cereal rye and that feral populations have diverged regionally from one another. Reproductive isolation from domesticated rye, due both to the loss in popularity of the crop and to phenological shifts in feral rye relative to cultivars, may be contributing to the rapid evolution of this weed away from its domesticated ancestor in less than 120 yr since its introduction.