Factors affecting flower development and quality in Rhododendron simsii

As part of the genus Rhododendron, azalea is well known for its luxuriant flowering. High-quality flowering is essential and is considered to be a homogeneous bud burst in the forcing greenhouse and a continuous development to fully open flowers at indoor conditions. Growers continuously strive to improve the quality of their products and a simple question arose: “Why do azalea flowers not always open at indoor conditions?” We tried to answer this question by an in-depth physiological approach of the complex flowering process. In a first part, we focused on the effects of altered production processes on flower differentiation and flower bud dormancy. The increased use of plant growth regulators (chlormequat, paclobutrazol) did not affect flower differentiation, but increased the need for cold to break flower bud dormancy. Overall, large genotypic variations were found. In the second part of this research, carbohydrate metabolism and source-sink relationships were investigated. Based on photosynthesis measurements and forcing experiments, we defined the minimal light level needed to force azalea. The reasons for the two main problems with flower quality (non-homogeneous flowering and the arrest of flower development at indoor conditions) have been identified and can be prevented by correct production techniques. First, flower homogeneity is influenced by the amount of cold which plants receive during the dormancy period. Unfulfilled cold requirements will lead to non-homogeneous flowering. Second, the arrest of flower opening at indoor conditions is due to insufficient leaf starch reserves. Forcing plants to flower with the appropriate amount of supplemental light will prevent this problem by building-up reserves before sale

Cold treatment breaks dormancy but jeopardizes flower quality in Camellia japonica L.

Camellia japonica L. is an evergreen shrub whose cultivars are of great ornamental value. In autumn, after flower bud differentiation, dormancy is initiated. As in many other spring flowering woody ornamentals, winter low temperatures promote dormancy release of both flower and vegetative buds. However, warm spells during late autumn and winter can lead to unfulfilled chilling requirements leading to erratic and delayed flowering. We hypothesized that storing plants at no light and low temperature could favor dormancy breaking and lead to early and synchronized flowering in response to forcing conditions in C. japonica ‘Nuccio’s Pearl’. Plants with fully developed floral primordia were stored at dark, 7∘C, and RH > 90% for up to 8 weeks. To monitor endodormancy release during the storage, we evaluated the content of abscisic acid (ABA) in flower buds and the expression profiles of five putative genes related to dormancy and cold acclimation metabolism in leaves and flower buds. In addition, the expression of four anthocyanin biosynthesis pathway genes was profiled in flower buds to assess the effect of the treatment on flower pigment biosynthesis. At 0, 4, 6, and 8 weeks of cold treatment, 10 plants were transferred to the greenhouse and forced to flower. Forced plant flower qualities and growth were observed. The ABA content and the expression profiles of two dormancy-related genes (CjARP and CjDEH) suggested that dormancy breaking occurred after 6–8 weeks of cold treatment. Overall, plants treated for 6–8 weeks showed earlier vegetative sprouting, enhanced, and homogeneous flowering with reduced forcing time. Prolonged cold treatments also reduced flower size and longevity, anthocyanin content, and pigment biosynthesis-related gene transcripts. In conclusion, the cold treatment had a promotive effect on dormancy breaking but caused severe drawbacks on flower quality

Adventitious rooting of Chrysanthemum is stimulated by a low red:far-red ratio

Adventitious rooting, a critical process in the vegetative propagation of many ornamentals, can be affected by both light intensity and light quality. We investigated the use of spectral light quality to improve adventitious rooting of Chrysanthemum morifolium cuttings by applying different combinations of blue, red and far-red light. Additionally, unrooted cuttings were treated before planting with two auxin transport inhibitors (TIBA and NPA) to study the effect of light quality on auxin biosynthesis and/or transport. Results showed that lowering the R:FR ratio (decreasing the phytochrome photostationary state, PSS) improved rooting significantly and decreased the inhibiting effect of the auxin transport inhibitor NPA. An extra decrease of PSS by adding blue light to a red + far-red spectrum further enhanced rooting. In contrast, adding blue light to solely red light decreased rooting, an effect which was more pronounced in combination with the auxin transport inhibitors TIBA and NPA. Our results show that phytochrome plays a role in adventitious root formation through the action of auxin, but that also blue light receptors interact in this process

Beworteling stek met lichtkleuren te sturen, maar lichtrecept noodzakelijk : onderzoek naar alternatieven voor stekpoeder

Wat te doen als je geen stekpoeder meer kunt gebruiken? Dan wordt de beworteling bij sommige gewassen een lastige kwestie. Door belichting met specifieke kleuren zijn zowel de vorming als het transport van auxine te sturen; het hormoon dat cruciaal is bij de beworteling. Het effect van de lichtbehandeling verschilt per gewas

Beworteling stek met lichtkleuren te sturen, maar lichtrecept noodzakelijk : onderzoek naar alternatieven voor stekpoeder

Wat te doen als je geen stekpoeder meer kunt gebruiken? Dan wordt de beworteling bij sommige gewassen een lastige kwestie. Door belichting met specifieke kleuren zijn zowel de vorming als het transport van auxine te sturen; het hormoon dat cruciaal is bij de beworteling. Het effect van de lichtbehandeling verschilt per gewas

Light quality and adventitious rooting : a mini-review

Efficient adventitious rooting is a key process in the vegetative propagation of horticultural and woody species. A well-rooted cutting is essential for optimal growth and high quality plants. The use of spectral light quality to influence adventitious rooting has been studied for many years, but got a lot more attention since LEDs came on the market for horticultural practices. Contrasting results of the effect of light quality on adventitious rooting are reviewed in this Paper. Even though more fundamental research is needed to easily determine which light quality can be used for a specific species, the use of LEDs for adventitiuus rooting is promising. For in vitro plantlets implementation can he done easily, for in vivo cuttings, the use of LEDs seems also promising in a multi-layered system. The controlled environment will lead to a year-round high quality rooted cutting Production

Flower differentiation of azalea depends on genotype and not on the use of plant growth regulators

Flowering is a complex process which starts with the induction and development of the flower buds. For azalea (Rhododendron simsii hybrids), flower induction was hastened by the application of chlormequat and took place within 11 days after treatment. Subsequent flower bud differentiation was not altered by the application rate of the plant growth regulators (PGR) chlormequat and paclobutrazol, nor by temperature or light sum. There were however, large genotypic variations in flower bud differentiation rate. For all cultivars a linear phase until flower primordia were fully differentiated and the style started to enlarge (flower bud stage 7), was followed by a slower final development (to stage 8). The linear phase was fastest for the semi-early flowering cultivars (‘Mont Blanc’, ‘M. Marie’ and ‘Otto’), requiring only 46 or 48 days to reach flower bud stage 7 after the first PGR treatment. Two late flowering cultivars (‘Thesla’ and ‘Sachsenstern’) had the slowest differentiation, requiring 64 days to reach stage 7. The early flowering cultivars (‘H. Vogel’ sports) and two late flowering cultivars (‘Mw. G. Kint’ and ‘Tamira’) required 54 and 52 days, respectively, after the first PGR treatment to reach stage 7. To reach flower bud stage 8, a similar trend in velocity was seen, the semi-early flowering cultivars requiring the least amount of days (17 to 18 days), the late flowering cultivars ‘Thesla’ and ‘Sachsenstern’ requiring the highest amount of days (24) and the early flowering cultivars and the late flowering cultivars ‘Mw. G. Kint’ and ‘Tamira’ requiring an intermediate number of days (20 to 22 days)

Flower development and effects of a cold treatment and a supplemental gibberellic acid application on flowering of Helleborus niger and Helleborus x ericsmithii

A

Changes in ABA levels in vegetative and flower buds during dormancy in Camellia

Camellia japonica L. is an evergreen acidophilic perennial, member of Theaceae Mirb. (Theales), that includes more than 3,000 named cultivars of great ornamental value. Bud dormancy is a key adaptive trait during the annual cycle of overwintering temperate woody plants and is present in Camellia. There is sufficient evidence that abscisic acid (ABA) is responsible for the initiation and, in a number of species, also for the maintenance of endodormancy. Increase of endogenous ABA is generally observed at the onset of endodormancy, while loss of bud dormancy is linked to declining ABA levels. To deepen our understanding of the role of ABA in C. japonica during dormancy, both vegetative and flower buds were studied. In a first experiment, we assessed the seasonal dynamics of ABA in vegetative buds from the onset of dormancy to its release. In this case, the results described a complex type of response, with several peaks of ABA in the middle of dormancy, and a major peak followed by a drastic reduction right before dormancy release of the vegetative bud. The second experiment concerned the quantification of ABA in flower buds during a cold treatment (7°C) performed after dormancy onset. Here, the results indicated a clear downward trend of flower buds ABA levels in response to increasing periods at constant low temperatures. Overall, morphological and physiological data confirmed the critical role of cold in the release of endodormancy in camellia. Future studies concerning the release of bud dormancy and correlated ABA levels in response to cold should focus on a wide range of C. japonica cultivars. This could allow selection of genotypes that bloom later in spring on the one hand (garden camellias) or genotypes that can be easily forced in flowering (flowering pot plants) on the other hand. This knowledge could also be exploited in breeding programs

Rooting of ornamental cuttings affected by spectral light quality

Adventitious rooting is a critical process in the vegetative propagation of ornamental plants. A well-rooted cutting is essential for optimal growth and high quality plants. We investigated the use of spectral light quality to improve adventitious rooting of cuttings in three ornamental species: Chrysanthemum x morifolium, Lavandula angustifolia and Rhododendron simsii hybrids (azalea). Different combinations of red (R) and blue (B) LEDs were tested: R:B 100:0, 90:10, 80:20, 50:50, 10:90 and 0:100 at a light intensity of 60 mu mol m(-2) s(-1) for chrysanthemum and lavender and 30 mu mol m(-2) s(-1) for azalea. No natural light was supplied. The rooting quality was assessed by determining the rooting percentage, the amount of roots and the root dry weight. For all three species, rooting was highly efficient under 100% red light. Polar auxin transport was also influenced by the different light spectra as demonstrated by the use of auxin transport inhibitors. For chrysanthemum, rooting was most inhibited under 10:90 R:B, while for azalea the inhibition in rooting was highest under 50:50 R:B. The use of LEDs for rooting of ornamental cuttings is promising if it can be used in a multi-layered system. The controlled environment will lead to a year-round high quality rooted cutting production