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Susan S. Han and Jennifer Nobel

The study was conducted to determine if ethylene or ethephon, an ethylene-releasing compound, can be used to induce abscission of phylloclades of four cultivars of Easter cactus [Rhipsalidopsis gaertneri (Regel) Moran] to increase efficiency in vegetative propagation. Abscission occurred within 24 hours after commencement of the ethylene treatments. Phytotoxicity, as exhibited by water soaking, transparency, and darkening of the phylloclades, as well as percent abscission, increased with increasing concentrations of ethephon (0 to 10,000 μl·liter–1). Ethylene released from ethephon, not the acidity of the solution, was determined to be the cause of the phytotoxicity. In three out of the four cultivars, vegetative and root growth from propagated phylloclades was significantly restricted by treatments with ethephon. In comparison, vegetative growth from phylloclades treated with ethylene at 20 μl·liter–1 was the same as from those treated with air. Root growth of the ethylene-treated phylloclades was not studied. The acidity of the ethephon solutions likely affected the growing regions, resulting in a reduction in growth. The study shows that treatment with ethylene gas or the use of pH-adjusted ethephon solutions may be an alternative to the labor-intensive procedures associated with vegetative propagation of Easter cactus. Chemical name used: 2-chloroethylphosphonic acid (ethephon).

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Susan S. Han and Jennifer Nobel

Whitefly infestation of poinsettias arises frequently from cuttings that were infested at the start of the season. Experiments were conducted to investigate the feasibility of using short-term elevated CO2 to eliminate whiteflies on cuttings prior to planting. Results indicated that adult greenhouse whiteflies (Trialeurodes vaporarium) are highly susceptible to an elevated level of CO2. All adult whiteflies are killed after exposure to 25% or 50% CO2 for less than 10 hours. Eggs, however, are more resistant than adults where 80% survived 10-hr of 50% CO2 treatment. Tests on poinsettia cuttings demonstrated that prolonged exposure to elevated CO2 resulted in the development of toxic symptoms soon after the treatments. Tolerance of 'Lilo' exceeded that of 'Supjibi', revealing differences in susceptibility of the two cultivars to the elevated CO2 treatment. Believing that the reduction in O2, rather than the elevation of CO2, was the main cause of mortality, we are currently testing the effects of hypoxia on survival of whiteflies.