Nature and Genetic Control of the Vernalization Response In Phalaris Tuberosa L.

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Abstract
Vernalization of seed promoted flowering in P. tuberosa, particularly in ecotypes with an obligate cold requirement. The rate of thermoinduction was slower in seed than in seedlings, but all ecotypes responded to seed vernalization by flowering earlier and at a smaller leaf number. Combinations of vernalization of seed and seedling were additive in their promotion of flowering. Attempts to replace the inductive effect of low temperature with either short days or gibberellin treatment were not successful. Short days had a slight inductive effect, but only at intermediate temperatures close to the vernalizing range. Selection for vernalization requirement indicates that there is considerable additive genetic variation for this character in the Australian cultivar and that it is under polygenic control. Response to selection in both directions was rapid, and the difference in vernalization requirement between the high and low lines after 4 generations of selection was greater than the total range found among naturally occurring ecotypes. The vernalization requirement appears to be relatively independent of seedling growth characters, but is correlated with flowering time both in controlled environments and in the field. In view of the considerable genetic variation stored in populations of P. tuberosa, and the high heritability (0.63 [plus or minus] 0.06) found for the vernalization response, it should be possible to select for plants which will remain vegetative indefinitely when grown in a mild winter environment.