Flowering of Australian wheats and its relation to frost injury

Abstract

It is known that the onset of the reproductive stage in wheat is an important factor in determining severity of damage by frost. Nineteen Australian and five overseas varieties have been tested for their sesponse to cold treatment of the seed (vernalization) and length of day (photoperiod), two factors known to influence ear formation. Many of the Australian wheats, although of the spring type, show small but, definite acceleration of ear initiation after vernalization treatment, although the period of ear development after initiation is unaffected. The Australian winter type of Minflor behaves similarly, but with a greater acceleration, characteristic of its winter habit. Minflor Winter wheat may be vernalized by cold temperature not only as a seed, but at any time during vegetative growth. Neither guanosine nor gibberellin replaced vernalization in a winter wheat. Short (9 hr) photoperiod delays ear initiation in all varieties, vernalized or non-vernalized, compared with continuous light, but varieties differ greatly in their sensitivity to day length. After initiation, some varieties are relatively unaffected by short day in the development of the ear, while others continue to be delayed. Minflor Winter is one of the varieties least delayed by short day. No 'short day induction' of unvernalized plants could be demonstrated, although there was an early period of indifference to day length in both a spring and a winter variety. Field behaviour in the light of the vernalization and photoperiodic responses, and their influence on frost escape, are discussed. In view of the genetic bases of these responses, the wider employment of controlled conditions is likely to prove useful to Australian wheat breeders in the future.