HORTSCIENCE 36(5):953–954. 2001. Received for publication 20 Sept. 2000. Accepted for publication 24 Jan. 2001. Florida Agricultural Experiment Station Journal series No. R-04566. This research was supported in part by grants from the American Flower Endowment and Junta de Investigação Científica e Tecnológica (Programa Ciência, Portugal). We thank Yoder Brothers (Parrish, Fla.) for supplying the plants. The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regulations, this paper therefore must be hereby marked adver- tisement solely to indicate this fact. 1 To whom reprint requests should be addressed; current address: University of Algarve, UCTA, Gambelas, 8000 Faro, Portugal. E-mail address: jmontei@ualg.pt High Production Temperature Increases Postproduction Flower Longevity and Reduces Bud Drop of Potted, Miniature Roses ‘Meirutral’ and ‘Meidanclar’ José A. Monteiro 1 , Terril A. Nell, and James E. Barrett Department of Environmental Horticulture, University of Florida, Gainesville, FL 32611 Additional index words. keeping quality, night interruption, Rosa sp. Abstract. The effect of two temperature regimes (29 °C day/24 °C night and 24 °C day/18 ° C night) and of a 4-hour night interruption, during production, was studied on postproduction flower longevity and bud drop of ‘Meirutral’ and ‘Meidanclar’ potted, miniature roses (Rosa L. sp.). High production temperatures increased postproduction flower longevity and decreased postproduction bud drop. In ‘Meidanclar’, the high production temperature increased incidence of malformed flowers. No effects of night interruption could be shown on either postproduction flower longevity or bud drop. Postproduction flower longevity in potted miniature roses (Rosa L. sp.) is greater in plants produced in summer than in those pro- duced in winter, spring, or fall (Andersen et al., 1992; Chen, 1990). When ‘Meijikatar’ and ‘Meirutral’ miniature roses were grown in a growth chamber under long days (14 h) and high temperatures (30 °C day/21 °C night), flower longevity was greater than in plants grown under short days (10 h) and low tem- peratures (21 °C day/16 °C night) (Kyalo et al., 1996). The increased flower longevity could be the result of the high temperature, the increased daylight integral, a phytochrome- mediated response, or a combination of these three factors. The objective of this work was to assess the effect of production temperature and night interruption on postproduction flower longevity and bud drop of ‘Meirutral’ and ‘Meidanclar’ potted, miniature roses. ‘Meidanclar’ was included in the study; its pattern of flower senescence differs from that of ‘Meirutral’ (Monteiro et al., 2001). Materials and Methods Rooted cuttings of ‘Meirutral’ and ‘Meidanclar’ roses (Yoder Brothers, Parrish, and a 12-h photoperiod of 12 μ mol·m –2 ·s –1 PAR from cool-white fluorescent bulbs. Buds were divided into two stages: a) showing color with the sepals starting to separate (stage 1) and b) green buds (stage 0). Flower longevity refers to buds that opened in the interior rooms, and was established as the period from anthe- sis to flower death (flower drop, petal wilt, petal drop, or petal browning, whichever came first). The buds that failed to open because of bud drop, bud yellowing, or bud browning were counted under the general designation of bud drop. Since night interruption effects were nonsignificant, data from the two night inter- ruption treatments were pooled and tempera- ture effect was analyzed performing a two- sample t test for the equality of the means (Ttest Procedure, SAS software, SAS Insti- tute, Cary, N.C.). Percentage of bud drop was analyzed with the transformed variable PD = arcsin[square root (% of bud drop)]. Results and Discusssion Growing the plants at HT increased flower longevity and decreased bud drop (Table 1). In ‘Meidanclar’, temperature did not affect bud drop of stage 0 buds (Table 1). Nevertheless, under HT conditions ‘Meidanclar’ plants tended to have malformed flowers (overgrown, leafy ovaries); thus, the high temperature used in this experiment is unsuitable for commer- cial production of this cultivar. Possibly, tem- peratures in-between the ones used in this experiment would maintain the beneficial ef- fects on flower longevity and bud drop, with- out the detrimental effects on ‘Meidanclar’ flower morphology. Growing at high temperatures would not be expected to improve overall net CO 2 ex- change rates, as the optimal temperatures de- termined for similar cultivars (i.e., ‘Meijikatar’ and ‘Meilarco’) are ≈15 to 20 °C (Jiao et al., 1990). Modified priorities on carbohydrate partitioning seem a better explanation. Low night temperatures (12 ºC, as opposed to 18 °C) promote carbon translocation to the basal parts of rose plants, reducing the levels of reducing sugars in flower petals (Khayat and Zieslin, 1989). Also, since high temperature induces smaller flowers (Kyalo et al., 1996), reduced flower size may reduce the flower’s need for carbohydrates to achieve normal open- ing and development, thus increasing postproduction performance for the same amount of available carbohydrates. Summer production–increased longevities are, at least, partly due to the increase in Fla.) were grown, one cutting per 0.4-L plastic pot, as described by Monteiro (1993). Plants were grown at warm temperature (WT), 24 °C day/18 °C night, or high temperature (HT), 29 °C day/24 °C night, as well as with incandes- cent lights from 2200 to 0200 HR or without night interruption, in a split-plot experimental design with temperature as a whole plot. All plants were covered with black opaque cloth from 1630 to 0800 HR to supply a uniform 8.5- h photoperiod. The experiment included five repetitions over time: three repetitions in air- conditioned greenhouses (planting dates: 19 June, 25 July, and 21 Aug. 1992) and two in high-irradiance rooms (planting dates: 1 Oct. 1992 and 5 Mar. 1993). Each repetition in- cluded at least four plants per treatment. ‘Meirutral’ was included in all five repeti- tions, ‘Meidanclar’ only in the last three (once in the greenhouses, twice in the high-irradi- ance rooms). Light levels at plant canopy at noon on sunny days ranged from 900 to 1100 μ mol·m –2 ·s –1 photosynthetically active radia- tion (PAR) in the greenhouses and 600 ± 80 μ mol·m –2 ·s –1 PAR in the high-irradiance rooms (Sylvania 1000 Metalarc R bulbs; Osram Sylvania, Danvers, Mass.). To evaluate postproduction longevity, plants were moved to interior rooms when at least two buds showed color, with sepals start- ing to separate. Conditions in interior rooms were 21 ± 1 °C, 50% ± 5% relative humidity, Table 1. Effects of production temperature regime on flower longevity and bud drop, under interior conditions, of ‘Meirutral’ and ‘Meidanclar’ miniature roses. (Interior rooms provided a 12-h photo- period of 12 μmol·m –2 ·s –1 PAR, 21 ± 1 ºC, and 50 ± 5% relative humidity). Flower longevity (d) Bud drop (%) Temp (ºC) Meirutral Meidanclar Meirutral Meidanclar (day/night) Stage 0 z Stage 1 Stage 0 Stage 1 Stage 0 Stage 1 Stage 0 Stage 1 29/24 9.0 11.1 10.2 12.0 58.8 4.8 66.3 0.8 24/18 2.2 5.3 7.7 8.9 98.3 61.4 73.8 48.3 Significance y 0.0001 0.0001 0.0001 0.0001 0.0001 0.0001 0.3894 0.0001 z Stage 0 = green buds; Stage 1 = buds showing color with sepals starting to separate. y P values for temperature effect (two-sample t- test, two tailed).