Cytogenetic and evolutionary studies in Secale. III. Cytogenetics of weedy ryes and origin of cultivated rye

Abstract

Several weedy forms of rye which have been variously recognized as varieties, subspecies or even species, and a new collection of primitive rye were crossed with the cultivated variety 'Merced'. They all crossed readily and produced vigorous F1's with normal meiosis and with F1 pollen fertility nearly as high as that of the parental materials. No evidence of structurel differences between the genomes of weedy ryes and cultivated rye was found. On the grounds of similar chromosome arrangements, identical breeding habits, equal periodicity, morphological continuity, crossability, regular meiotic behavior of their hybrids, normal F1 pollen fertility and geographical continuity, it is concluded that all these forms should be recognized as subspecies of S. cereale. Study of the meristematic activity of the seedlings of four strains of rye showed that forms with larger grains had greater meristematic activity, while those with smaller grains had less. It is concluded that large-grained forms originated probably by the accumulation of mutations causing increase in grain size because large-grained forms had adaptive advantage due to their better competitive ability. Similarly, it is suggested that the stiff rachis evolved due to unconscious selection by primitive farmers for polygenes conditioning that character. A figure showing the distribution of weedy ryes and the centers of maximum diversity is given. It is concluded that rye was first domesticated at several places independently and at different times. Cultivation of rye probably entered Europe by two routes: through northern Caucus and through central Asia.