Temperature impacts changes in crown buds and flowering of gentian ‘Spotlight’

Abstract

A better understanding of the origin and development of crown buds in gentian may help explain the observed spread in timing of flower harvest maturity. The types and numbers of buds, the time of their macroscopic appearance, emergence and development to flowering were tracked over time, in two growing environments for two growth cycles of the gentian cultivar ‘Spotlight’. Although different types of buds were present, only pre-formed primary-crown buds produced flowering shoots. In the first growth cycle, only 73% of these pre-formed buds emerged, leaving the rest of the buds to senesce and degenerate. Hence, the observed spread in time of flower harvest maturity was not due to either bud type or buds that appeared during the current growth cycle developing into floral shoots. The appearance of new crown buds for the following growth cycle's flower production occurred over an 8-month period, from summer through to winter. The time of harvest maturity for a shoot was not strongly correlated with the time of bud appearance or shoot emergence, as originally hypothesised. Compared with those grown in the cooler environment outside, cultivation in a protected environment resulted in 50% longer shoots at harvest, did not influence the time to flower harvest, but increased the rate of appearance of buds by an additional 0.18 per month. With no chilling however, within the protected environment the crown buds failed to emerge as shoots during the second growth cycle. In contrast, with chilling received by outdoor-grown plants, crown buds emerged and flowered. The lack of any correlation between the time of appearance of buds and/or their emergence with that of stem harvest maturity, as well as the chilling requirement for shoot emergence, highlights that factors associated with growth and development of a crown bud after its appearance may have a greater influence on the time of harvest maturity in ‘Spotlight’ and, therefore, the spread in timing.