Plants of Begonia x tuberhybrida ‘Nonstop’, ‘Clips’, and ‘Musical’ were exposed to 1, 2, 3, or 4 weeks of short
days (SD, 9 hours day length) initiated at 3 stages of plant development (immediately upon germination, 4
or 8 weeks after germination). Prior to and succeeding short days, plants were exposed to long days (LD, 16
hours day length). Musical flowered on average 68 days, Clips 78 days and Nonstop 83 days after germination under continuous LD conditions. In Nonstop, SD for 1, 2, 3, or 4 weeks delayed plant development by an average 12 days compared to LD grown plants. One, 2, or 3 weeks of SD resulted in 1 week slower flowering and 4 weeks of SD resulted in 2 weeks later flowering in Clips. The sensitivity to SD varied with plant stage in Musical. Three or 4 weeks of SD initiated at germination or 4 weeks after germination resulted in an average delayed flowering of 13 days compared to LD plants.  SD initiated 8 weeks after germination had no effect on rate of development in Musical

Karlsson, Meriam G.

Werner, Jeffrey W.

English

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Photoperiodic Control of Growth andDevelopment in ‘Nonstop’ Cultivar Seriesof Begonia x TuberhybridaMeriam G. KarlssonAssociate Professor of HorticultureAgricultural and Forestry Experiment StationUniversity of Alaska FairbanksJeffrey W. WernerStudent AssistantAgricultural and Forestry Experiment StationUniversity of Alaska FairbanksCircula r  91  July 1992Agricultural and Forestry Experiment S tationSchool of Agriculture and Land Resources ManagementU A FNIVERSITY OF LASKA AIRBANKSABSTRACTPlants of Begonia x tuberhybrida ‘Nonstop’, ‘Clips’,and ‘Musical’ were exposed to 1, 2, 3, or 4 weeks of shortdays (SD, 9 hours day length) initiated at 3 stages ofplant development (immediately upon germination, 4or 8 weeks after germination). Prior to and succeedingshort days, plants were exposed to long days (LD, 16hours day length). Musical flowered on average 68days, Clips 78 days and Nonstop 83 days after germina-tion under continuous LD conditions. In Nonstop, SDfor 1, 2, 3, or 4 weeks delayed plant development by anaverage 12 days compared to LD grown plants. One, 2,or 3 weeks of SD resulted in 1 week slower floweringand 4 weeks of SD resulted in 2 weeks later flowering inClips. The sensitivity to SD varied with plant stage inMusical. Three or 4 weeks of SD initiated at germina-tion or 4 weeks after germination resulted in an averagedelayed flowering of 13 days compared to LD plants.SD initiated 8 weeks after germination had no effect onrate of development in Musical.INTRODUCTIONThe ‘Nonstop’ series of Begonia x tuberhybrida Voss.was introduced during the 1970s by Benary Seeds ofGermany (Ewart, 1985). These Nonstop cultivars arepropagated by seed, have uniform growth over a widerange of environmental conditions and have semi-ns, *, **, *** Nonsignificant or significant at P < 0.05, 0.01 or 0.001, respectively.Duration of SD Days to Flower(weeks) Nonstop Clips0 83 781 94 852 95 893 95 894 97 97SignificanceControl vs. SD treatments *** ***Control vs. 1 week of SD *** *Control vs. 2 weeks of SD *** **Control vs. 3 weeks of SD *** **Control vs. 4 weeks of SD *** ***Duration, linear *** ***Duration, quadratic ** nsDuration, cubic * nsDuration, quartic ns nsdouble flowers in many colors. In addition to theNonstop series, many other seed propagated cultivarseries have been introduced and are produced com-mercially today.Tuberous begonias (B. x tuberhybrida) producetubers under short days (SD) and low temperatures(Peter, 1974; Fonteno and Larson, 1982; Oloomi andPayne, 1982; Fonteno and Larson, 1983; Djurhuus,1985; Ewart, 1985; Tonecki, 1986). In contrast to B. xhiemalis (hiemalis begonia, elatior begonia, Riegerbegonia), continuous long days (LD) and tempera-tures above 17 °C are required for proper plant devel-opment and flowering of tuberous begonia. Oncetuber formation has started, tuberous begonia plantswill not easily revert back to vegetative growth andflower formation (Ewart, 1985).Cultural recommendations for the seed propa-gated tuberous begonias are primarily based on ex-periences with cultivars propagated by tubers. Oneexample of such a recommendation is never to allowSD exposure of seed propagated tuberous begoniaafter germination. SD conditions are expected toresult in plant dormancy and tuber formation al-though the cultivars used today may respond differ-ently to photoperiod than the traditionally growntuberous begonias. This study was initiated to deter-mine the sensitivity of seed propagated tuberousbegonia to SD exposure during different stages ofplant development.1Table 1. Days to flower in Begonia x tuberhybrida ‘Nonstop’ and ‘Clips’ after exposure to short days (SD, 9 hours day length)for different durations during plant development. The remaining development occurred under a 16–hour photoperiod.Duration of SD Stage of SD Exposure(weeks) Early Intermediate LateDays to Flower0 68 68 701 72 70 722 74 68 693 77 79 734 83 85 68SignificanceControl vs. SD treatments ** ** nsControl vs. 1 week of SD ns ns nsControl vs. 2 weeks of SD * ns nsControl vs. 3 weeks of SD ** ** nsControl vs. 4 weeks of SD *** *** nsDuration, linear *** *** nsDuration, quadratic ns * nsDuration, cubic ns ns nsDuration, quartic ns ns nsns, *, **, *** Nonsignificant or significant at P < 0.05, 0.01 or 0.001, respectively.Table 2. Days to flower in Begonia x tuberhybrida ‘Musical’ after exposure to different durations of short days (SD, 9 hoursday length) initiated at the growth stages of germination (early), intermediate (4 weeks after germination) or late stage (8weeks after germination). The remaining development occurred under a 16–hour photoperiod.were randomized within each cultivar andrerandomized as SD treatments were initiated or com-pleted. There were 10 plants in each treatment. Flower-ing was recorded when the first bud on the plantshowed color. Data on time to flower, shoot, leaf andflower number, leaf area, and dry weight were col-lected 105 days after germination to allow most plantsto flower. The results in the text are given as the meanof the plants in a treatment ± SE (standard error).RESULTS AND DISCUSSIONThe time required for plants to flower under con-tinuous LD conditions throughout the developmentwas significantly different for the three cultivars (Fig-ure 1). Flowering in Musical was observed 68 ± 1.7 daysfrom germination. Clips flowered on average 10 dayslater or 78 ± 1.3 days from germination and Nonstopwas the slowest developing cultivar requiring 83 ± 1.7days for flowering. The least significant difference(P=0.05) for average number of LD to flowering amongcultivars was 4.1 days.Statistical analyses of the photoperiodic effects onrate of plant development within each cultivar showedhighly significant effects of SD duration. HoweverPROCEDURES‘Nonstop Orange’, ‘Clips Orange’, and ‘MusicalOrange’ were the cultivars selected for this study. Seedwas germinated at 21–24° C media temperature and 24hours of light. The experiment was initiated 2 weeksafter seeding. Plants at different stages of developmentwere placed under SD for variable duration and thenreturned to LD. The photoperiod during SD was 9hours at a photosynthetic photon flux (PPF) of 180 ± 20µmol • m -2 s -1. PPF level during the 16–hour LD periodwas 100 ± 10 µmol • m -2 s -1. The instantaneous PPFlevels from high-pressure sodium lamps were selectedto provide similar total daily PPF of 5.8 mol m -2day -1for both the 9– and the 16–hour day length. The daytemperature was maintained at 21 ± 2°C and the nighttemperature at 18 ± 2 °C. The day and night periods forthe temperatures followed the 9–hour photoperiod togive an average daily temperature close to 19° C. Stagesof plant development for SD exposure were at germina-tion (2 weeks after seeding), 4 or 8 weeks after germina-tion. The plant stages for initiation of SD will be re-ferred to as early, intermediate and late. The duration ofSD exposure was 0, 1, 2, 3, or 4 weeks. The treatmentswere arranged in a factorial experiment and plants25060708090100abcNonstop Clips MusicalDays to Flower847868Figure 1. Days to flower in Begonia x tuberhybrida ‘Nonstop’, ‘Clips’, and ‘Musical’ grown under 16-hour photoperiod.Treatments identified with the same letters are not significantly different by the least significant difference (lsd), P = 0.05.there were no significant effects of plant stage at SDexposure or the interaction of plant stage by SD dura-tion in Nonstop and Clips. The data were thereforepooled over the different plant stages in Nonstop andClips. Rate of development in Musical was signifi-cantly (P=0.05) affected by the plant stage at SD expo-sure and by the interaction between plant stage and SD.Average days required for flowering in Nonstopand Clips after exposure to different durations of SDare presented in Table 1. The delay in Nonstop plantswas similar for 1, 2, 3, or 4 weeks of SD exposurecompared to the plants under continuous LD. On aver-age, 95 ± 0.9 days were required for flowering in Non-stop after any SD during plant development. Nonstopplants maintained under LD conditions required anaverage 83 ± 1.7 days to flower. For Clips plants, therewas a trend for slower development with increasingnumber of SD weeks (Table 1). Four weeks of SDresulted in an average 19 days slower flowering com-pared to the control plants of Clips.Plant stage at initiation of SD altered the influenceby short photoperiods in Musical (Table 2). Duringearly development, longer exposure to SD resulted inprogressively larger delay with an average 15 daysslower flowering after 4 weeks of SD. Three weeks ofSD initiated during intermediate plant stage resulted inflowering 79 ± 2.2 days after germination compared toflowering in 68 ± 1.7 days under LD. The delay for a 4–week SD period during intermediate development was17 days. There were no significant effects on rate ofdevelopment by SD initiated during late developmentin Musical.Sensitivity of developmental rate to SD varied withcultivar in seed propagated tuberous begonia. Nonstopresponded with delayed development even after 1week of SD at any time during growth (Table 1). In-creasing the length of SD from 1 to 2, 3, or 4 weeks didnot appear to affect the amount of delay in Nonstop. SDfor 1, 2, or 3 weeks resulted in 1 week and SD for 4 weeksin 2 weeks later flowering in Clips (Table 1). Indepen-dent of when the short photoperiod was initiated dur-ing development, there were no significant delay inMusical following 1 SD week (Table 2). Musical plantsresponded with slowed development especially after 3or 4 weeks of SD during early or intermediate develop-ment. Plants of any cultivar kept under SD throughouttheir development grew very slowly, having 3 or 4leaves 100 days after germination.There were no significant differences among plantsfrom SD treatments within cultivars with respect toplant size characteristics. Musical plants were the larg-est plants and Nonstop the smallest plants of the 3cultivars. Musical had an average of 5 ± 0.1 shoots perplant, Clips 4 ± 0.4, and Nonstop 2 ± 0.2. Leaf and flowernumber on the main shoot were 12 ± 0.5 and 8 ± 0.9; 10± 0.4 and 4 ± 0.6; and 8 ± 0.1 and 3 ± 0.1 for Musical, Clipsand Nonstop respectively. Total average leaf area perplant for Musical, Clips and Nonstop were 836 ± 55cm 2, 659 ± 73 cm 2 and 485 ± 56 cm 2 respectively. Thecalculated average leaf size for the whole plant was3largest in Nonstop with 45 cm 2 followed by 27 cm 2 forClips and 23 cm 2 for Musical. Plant height at the termi-nation of the experiment was different among cultivarsbut not within cultivars. The average plant height was19 ± 0.5 cm for Musical, 15 ± 1.1 cm for Clips and 12 ± 0.4cm for Nonstop.Exposure to SD was expected to result in slowedgrowth and higher proportion of root dry weight (Pe-ter, 1974; Fonteno and Larson, 1982; Oloomi and Payne,1982; Fonteno and Larson, 1983; Djurhuus, 1985; Ewart,1985; Tonecki, 1986). Though shoot weight respondedto SD, there were no significant differences in root dryweight among plants in different SD treatments. Musi-cal plants had an average root dry weight of 2.7 ± 0.31gram, Clips plants 2.7 ± 0.12 gram and Nonstop 2.3 ±0.12 gram root dry weight per plant. Total plant dryweight among plants varied correspondingly amongcultivars such that the percentage root dry weight in aplant was close to 50% for all 3 cultivars.REFERENCESDjurhuus, R. 1985. The effects of photoperiod andtemperature on growth and development ofBegonia x tuberhybrida ‘Karelsk Jomfru’. ScientiaHortic. 27:123-131.Ewart, L.C. 1985. Tuberous rooted begonia. In: J.W.Mastalerz and E.J. Holcomb (eds.). Bedding plantsIII, a manual on the culture of bedding plants as agreenhouse crop, Third edition, p. 420-422. Pennsyl-vania Flower Growers.Fonteno, W.C. and R.A. Larson. 1982. Photoperiod andtemperature effects on NonStop tuberous begonia.HortScience 17:899-901.Fonteno, W.C and R.A. Larson. 1983. Flowering controlfor NonStop tuberous begonia. North Carolina FlowerGrowers Bulletin 27(3):1-3.Heide, O.M. and W. Rünger. 1985. Begonia. In: A.H.Halevy (ed.). Handbook of flowering, volume II, p. 4-23. CRC Press, Inc., Boca Raton.Oloomi, H. and R.N. Payne. 1982. Effects of photope-riod and pinching on development of Begonia xtuberhybrida. HortScience 17:337-338.Peter, J. 1974. Einfluss der Temperature auf dasoberirdische Wachstum und die Knollenbildungbei Begonia x tuberhybrida (Voss.).Gartenbauwissenschaft 39(3):301-308.Tonecki, J. 1986. Effects of short photoperiod and growthregulators on growth, flowering and tuberizationof Begonia x tuberhybrida. Acta Horticulturae 177:147-156.4

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