Long Term Low Concentration Ethylene Exposure Affects Growth, Flowering and Development of 28 Ornamental Taxa

Five plants each of 28 ornamental taxa were grown in equivalent greenhouse environments for two weeks after transplanting.  Ethylene was released daily for six more weeks in each house from 4 p.m. to 9 a.m. to achieve the treatment concentration of 0, 0.01 or 0.05 μL · L^-1 ethylene.  Growth and development responses were measured by number of abscised organs, flower counts, plant height, diameter, fresh and dry weight.

         Increased growth of Ocimum basilicum L., Solenostemon scutellarioides (L.) Codd, and Dahlia Cav. was positively correlated with ethylene concentration.  Cuphea hyssopifolia Kunth, Lobelia erinus L., and Osteospermum ecklonis (DC.) Norl. grew larger at 0.01 μL · L^-1 ethylene than at either 0, or 0.05 μL · L^-1 ethylene.  Increased growth was negatively correlated to ethylene concentration for Gerbera jamesonii Bolus ex Hook. f., Capsicum annuum L., Solanum lycopersicum L., and Petunia integrifolia (Hook.) Schinz & Thell.  While ethylene inhibited lateral branch growth of Fuchsia hybrida hort. ex Siebold & Voss, Calibrachoa Llave & Lex. and Portulaca oleracea L., it promoted the same for Ocimum basilicum, Lobelia erinus and Cuphea hyssopifolia.

           Flowering was variably inhibited by any ethylene amount for most taxa though some partially recovered from the effect over time.  Where flowering did occur in ethylene’s presence, flower size was reduced and flower senescence was more rapid compared to control.  Interestingly, 0.01 μL · L^-1 ethylene inhibited flowering of Antirrhinum majus L. yet 0.05 μL · L^-1 did not. 
            Clearly, a given ethylene concentration can be a growth inhibitor for some species while for others it encourages growth.  Additionally, ethylene may encourage a specific response at one concentration while suppressing that same response at another concentration.  These results lend support to the hypothesis that ethylene response, whether growth promotion or inhibition, is incorporated into a single concentration dependent biphasic response model.