Control of flowering in Kalanchoë: physiological, hormonal and molecular aspects

Research output: Book/ReportPh.D. thesisResearch

  • Lívia Lopes Coelho
The ornamental plant industry is highly competitive and demanding for constant releases of newplant varieties with novel traits. Cross-pollination is the easiest and most commonly used techniqueto create new hybrids; however it is limited by the lack of knowledge on the control of floweringtime. The Kalanchoë genus occupies one of the leading positions among the most commercializedpotted plants in Europe. Even though the genus comprises great genetic variety due to the numberof species with different traits, only few are suitable for breeding programs. The lack of knowledgeon flower inductive factors is one of the main challenges for the inclusion of several Kalanchoëspecies in breeding programs. Therefore, the aim of this study was to use current knowledge frommodel plants to increase knowledge on flowering aspects within this genus, by using physiological,hormonal and molecular approaches. The control of flowering occurs in response to endogenousand environmental cues as a strategic evolutionary achievement that conferred higher plants toadapt to different environments. The nature and identity of the flowering signal intrigued scientistsfor over a century, and it was named florigen. In model plants, six flowering pathways have beenidentified, which are much conserved among angiosperms. Several studies conducted in the last twodecades revealed that the protein FLOWERING LOCUS T (FT) is part of the florigen complex,acting as the mobile signal that triggers flowering. Thus, the experiments conducted in the thesisinvestigated the effect of cold night temperatures and exogenous gibberellin application onflowering of different Kalanchoë species. Moreover, an experiment was conducted to characterizethe critical cycles of short days (SD) photoperiodic induction to correlate the flowering response tothe expression of the FT homolog in Kalanchoë gracilipes. In the first experiment (publication 1),the floral promotive effect of cold night temperature was observed in K. prittwitzii, when plantsexposed to 12°C at night produced more flowers compared to 18°C and 6 °C. Nevertheless, K.marmorata had inconsistent flowering and K. longiflora did not flower. Therefore, the temperaturewas not a requirement to induce flowering in neither species evaluated. K. longiflora and K. pinnatahad a higher percentage of flowering and increased numbers of flowers and inflorescences whentreated with gibberellin; however the hormone applications have a subsidiary effect on flowering onboth species (publication 2). Furthermore, besides triggering flowering, prolonged exposure to SDphotoperiodic treatment enhanced flowering of K. gracilipes. The molecular analyses of the leavesand apical meristem revealed that one FT-like gene, KgFT1, is expressed in response to short dayinduction, being a good candidate to the florigen in this species (publication 3). A phylogenetictree constructed with genomic sequences of K. fedtschenkoi and K. laxiflora provides the firstinsight of the phosphatidyl ethanolamine-binding (PEBP) gene family within the genus(publication 4). Collectively, the results revealed great variation regarding flowering requirementswithin the Kalanchoë genus. While flowering requirements of K. longiflora was reported for thefirst time, the flowering requirement of K. marmorata remains unknown. Moreover, photoperiodwas confirmed to be the main requirement for flowering in the species studied, while nighttemperature and gibberellic acid only had secondary effects
Original languageEnglish
PublisherDepartment of Plant and Environmental Sciences, Faculty of Science, University of Copenhagen
Publication statusPublished - 2018

ID: 201161066