Towards control of flowering time of Protea cynaroides (L.) L. cv. Arctic Ice through studies of its bimodal inflorescence initiation and phenology

The marketing potential of Protea cynaroides (L.) L. cv. Arctic Ice, a popular, white King Protea selection, is limited by its flowering time. Despite having the potential for all-round flowering, current production is largely restricted to two distinct commercial harvest periods, in autumn and spring. However, most commercially grown P. cynaroides variants exhibit only coalesced harvests in spring, under southern hemisphere conditions. The largely unknown mechanism controlling floral initiation and flowering for King Protea poses a challenge to achieving marketing continuity of this niche cut flower. An ‘Arctic Ice’ flowering model is proposed which consists of bimodal floral initiation periods, occurring concurrently with seasonal vegetative flushing. Responsiveness to prevailing environmental conditions, along with lesser-known endogenous factors, are considered possible drivers for phenological events. Such factors may include episodic shoot flushing, synchronized inflorescence initiation, and irregular floral reversion. We present an observation- based report of inflorescence reversion. The indeterminate meristem of ‘Arctic Ice’ does not preform successive flushes nor floral appendages but produces primordia based on prevailing inductive conditions. Tracking of inflorescence buds recorded seasonal trends in maturation rates over 12 months. Winter-developing inflorescences required the longest time to harvest, ca. 20 weeks, while inflorescence buds that were first visible in summer, displayed a significantly shorter development time to harvest, approximately 16 weeks. The ‘Arctic Ice’ model suggests that for sustained production volumes to meet year-round market demand, alternative approaches to the current, conventional P. cynaroides management are required. New insights into the flowering phenology of P. cynaroides as reported in this study provide support for developing alternative approaches to achieve sustained production volumes of ‘Arctic Ice’ to meet year-round market demand. • Protea ‘Arctic Ice’ flowers in autumn and spring with reduced year-round flowering. • ‘Arctic Ice’ adheres to an alternate flowering model for commercially produced Protea. • Shoots function and should be managed as autonomous units. • Inflorescence reversion is a response to environmental conditions and reserves. • Flower buds develop slower through winter than summer.