Note to readers, attached is the complete final report for FNE96-141
Anyone who grows flowering ornamentals in a greenhouse knows that considerable time and effort must be devoted to pinching off the buds, to prevent them from flowering too early for the market. A low-cost alternative to pinching by hand is to spray the plants with ethylene, a simple (C2H4), naturally-occuring plant hormone, which causes flowers to drop. Some time after the exposure is terminated the plant will flower again; thus a grower may, with judicious use of ethylene, assure that his plants are in flower at just the right moment. Further, since plants that are not in flower will devote more photosynthate to vegetative growth, use of ethylene makes possible production of bushier, more attractive plants.
Timing, duration of the exposure, and dosage are all critical to the effective use of ethylene. Dr. Konjoian used his SARE grant to examine the effects of exposures of various durations on two species of ornamentals– impatiens and chrysanthemum. In a replicated experiment Dr. Konjoian grew impatiens in a greenhouse, sprayed the plants with a 500 ppm solution of ethylene after they had begun to flower, then washed them off, but varied the length of time between spraying and washing. He found that exposure to ethylene for as little as twenty minutes caused some flowers to drop. Exposures between two and twelve hours caused as much drop as not washing the ethylene off at all, however plants so treated did grow new flowers more quickly than the unwashed controls. Rates of drop and regrowth of flowers among plants exposed to ethylene for twelve hours or more were no different from those among the unwashed plants.
In another experiment, using chrysanthemums that had not yet begun to flower, Dr. Konjoian found that a one-hour exposure to ethylene caused a one-week delay in flowering. Longer exposures up to 24 hours caused longer delays; exposure to ethylene for 24 hours caused a two-week delay, which was the same as the delay observed among plants that were treated and left unwashed.
This information is useful to growers who may be interested in precise timing for the market, or in staggering maturity to assure a continuous supply. It also tells growers how soon after application of ethylene they may water their plants, and for those growing plants out-of-doors, whether or not a reapplication is necessary following a rain. Dr. Konjoian estimates that the substitution of ethylene for manual pinching may save two to three thousand dollars per year, per acre of greenhouse plants.