Growth and development of Oenothera fruticosa is influenced by vernalization duration, photoperiod, forcing temperature, and plant growth regulators

Influences of vernalization duration, photoperiod, forcing temperature, and plant growth regulators (PGRs) on growth and development of Oenothera fructicosa L. 'Youngii-lapsley' ('Youngii-lapsley' sundrops) were determined. Young plants were vernalized at 5 degreesC for 0, 3, 6, 9, 12, or 15 weeks under a 9-hour photoperiod and subsequently forced in a 20 degreesC greenhouse under a 16-hour photoperiod. Only one plant in 2 years flowered without vernalization, while all plants flowered after receiving a vernalization treatment, regardless of its duration. Thus, 0. fruticosa had a nearly obligate vernalization requirement. Time to visible bud and flower decreased by approximate to1 week as vernalization duration increased from 3 to 15 weeks. All plants flowered under 10-, 12-, 13-, 14-, 16-, or 24-hour photoperiods or a ii-hour night interruption (NI) in a 20 degreesC greenhouse following 15-weeks vernalization at 5 degreesC. Time to flower decreased by approximate to2 weeks, flower number decreased, and plant height increased as photoperiod increased from 10 to 16 hours. Days to flower, number of new nodes, and flower number under 24 hour and NI were similar to that of plants grown under a 16-hour photoperiod. In a separate study, plants were vernalized for 15 weeks and then forced under a 16-h photoperiod at 15.2, 18.2, 20.6, 23.8, 26.8, or 29.8 degreesC (average daily temperatures). Plants flowered 35 days faster at 29.8 degreesC but were 18 cm shorter than those grown at 15.2 degreesC. In addition, plants grown at 29.8 degreesC produced only one-sixth the number of flowers (with diameters that were 3.0 cm smaller) than plants grown at 15.2 degreesC. Days to visible bud and flowering were converted to rates, and base temperature (T,) and thermal time to flowering (degree-days) were calculated as 4.4 degreesC and 606 degrees days, respectively. Effects of foliar applications of ancymidol (100 mg.L-1), chlormequat (1500 mg.L-1), paclobutrazol (30 mg.L-1), daminozide (5000 mg.L-1), and uniconazole (15 mg.L-1) were determined on plants vernalized for 19 weeks and then forced at 20 degreesC under a 16-h photoperiod. Three spray applications of uniconazole reduced plant height at first flower by 31% compared with that of nontreated controls. Ah other PGRs did not affect plant growth. Chemical names used: alpha -cyclopropyl-alpha-(4-methoxyphenyl) 5-pyrimidinemethanol (ancymidol); (2-chloroethyl) trimethylammonium chloride (chlormequat); butanedioic acid mono(2,2-dimethyl hydrazide) (daminozide); (2R, 3R+2S,3S)-1-(4-chlorophenyl-4,4-dimethyl-2-[1,2,4-triazol-1-yl] (paclobutrazol); (E)-(S)-1- (4-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl)-pent-1-ene-3-ol (uniconazole).