Chondrilla juncea L. in Australia. I. Some factors affecting flowering

Abstract

The interaction between day length and vernalization, and the influence of growth temperature on flowering, in Chondrilla juncea L. (skeleton weed) have been studied.

Bolting and floral initiation in unvernalized plants were suppressed in a 9-hr photoperiod. Increasing the photoperiod beyond 12 hr resulted in progressively earlier bolting and floral initiation, the critical day length being slightly less than 12 hr. Interrupting a 16-hr dark period by 1 hr of low-intensity light near its centre caused some plants to flower. Prior vernalization further accelerated bolting and flowering and reduced the dependence on day length. Vernalization, however, was not an obligate requirement. Post-bolting development was favoured by high temperatures.

It was concluded that flowering in skeleton weed occurred in two stages. The first or photo-inductive phase was controlled by at least two partial processes. These were vernalization and a photoperiodic response in which the length of the dark period was the critical factor.

The relationship of the flowering processes to the distribution of skeleton weed in Australia is discussed briefly.