The genus Streptocarpus contains ≈130 species (Hilliard and Burtt, 1971; Möller and Cronk, 2001). Hybrid streptocarpus, commonly called streptocarpus or cape primrose, are the most widely cultivated plants in the genus (Moore, 1957). Streptocarpus are flowering potted plants that grow and flower freely in interior or shaded outdoor areas. Leaf cuttings are commonly used by hobbyist growers or collectors (Ebert and Ebert, 1984), but commercial streptocarpus propagation requires a technique that produces more plants in a shorter time period. Modern streptocarpus cultivars are traditionally produced using F1 hybrid seed (Dole and Wilkins, 2005). Additionally, streptocarpus do not require an environmental stimulus such as daylength (photoperiod) or cool temperatures (vernalization) for flower induction and development. The new ‘Ladyslippers’ streptocarpus series are propagated using tissue culture (Uhl, 2012). While these plants produce showy finished flowering plants, they regularly flower prematurely (i.e., while still in the liner tray) during greenhouse production, requiring hand labor to remove inflorescences.
Ethephon is a plant growth regulator (PGR) that is commonly applied as a foliar spray (Whipker et al., 2011b). When absorbed by plant tissue, the change in tissue pH causes ethylene gas to be generated within plant cells (Barrett, 2001). As a PGR, ethephon has several effects when applied to containerized ornamental crops (Barrett, 2001; Whipker et al., 2011b). Ethephon may act as a plant growth retardant and minimize stem elongation by reorienting microfibril orientation in cell walls; this causes cells to expand laterally and minimize elongation, which restricts stem height or length. Additionally, ethephon may be employed to increase branching in crops by increasing the ratio of ethylene : auxin, which diminishes apical dominance and releases axillary buds, resulting in enhanced lateral branch development. However, one of the most common uses of ethephon is to delay flowering for vegetatively propagated ornamental flowering crops (Dole and Wilkins, 2005). Flowering delay of vegetatively propagated material is generally desirable to extend the vegetative phase of production (i.e., growth of leaves) to increase the size or “bulk up” a containerized crop and reduce the disease pressure posed by senesced flowers.
We have found no published information on effective concentrations of ethephon for foliar spray applications on streptocarpus to inhibit or delay flowering. The objective of our experiment was to quantify the impact of foliar ethephon applications on the growth and flowering of tissue culture–propagated ‘Ladyslipper’ streptocarpus.
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