Flower initiation in Trifolium subterraneum L. II. Limitations by vernalization, low temperatures, and photoperiod, in the field at Canberra

Abstract

At various times throughout the winter, autumn-sown plants of five strains of subterranean clover were removed from the field to a series of day length and temperature treatments. The times to inflorescence initiation in all treatments were determined by dissection. As vernalization proceeded the requirement of all strains for long days was progressively reduced until, by midwinter, several strains had become virtually independent of day length. Similarly, with the progress of vernalization the inhibitory effects of high temperatures during short days became progressively less marked. Whereas exposure to long days at high temperatures greatly accelerated inflorescence initiation in all strains, long days at low field temperatures had little effect. Evidence is presented which suggests that the limiting effect of very low temperatures on initiation is due not only to retardation of the rate of inflorescence primordium formation (realization), but also to limitation of an inductive process other than vernalization and dark period inhibition. The flowering behaviour of the various strains is discussed in terms of their responses to the partial processes leading to inflorescence initiation, and the interrelationships of these processes are considered.