1. Flower Induction in the Floriculture Industry HRT 301 Roberto G. Lopez Purdue University

2. Juvenility (plant size) Photoperiod (day length) Vernalization (cold treatment) Hormones (Ethylene) Outline What plant is this? (Hint: It’s not Arabidopsis!!)

3. Flowering Can Be Influenced By: Juvenility – plant size or maturity Environmental signals – Cold (vernalization) – Photoperiod (day length) – Dormancy sequence Hormones – Ethylene

5. Question: Why did only the 50- cell-sized coral bells flower in the previous example? Answer: It’s a matter of age or Juvenility! Heuchera (Coral bells) flowering in Yosemite National Park

6. Juvenility A young stage of plant development in which plants from seed are not capable of flowering

7. Juvenility Juvenile period of woody plants usually lasts many years (Table 25.1 in text) For most herbaceous perennials usually less than one year.

8. Plant Developmental Stages Juvenile stage Mature stage

9. What is the best way for a grower to measure juvenility? Determine the average leaf number by: Counting a random group of many individuals seedlings and then calculate the average

10. Incomplete Vernalization of Perennials

11. Examples of Leaf Number Requirements for Flowering Herbaceous Perennials Aquilegia Some require 15+ leaves to flower consistently Aster alpinus Plants require at least 15 leaves to flower consistently Coreopsis ‘Sunray’ Juvenile phase ends with about 16 leaves Euphorbia epithymoides Plants with six to eight leaves failed to flower Goniolimon tatarica Plants with 10 to 14 leaves failed to flower Heuchera sanguinea Plants require 16 leaves to flower consistently Plant nameAge Requirements

12. Aquilegia ‘Origami Red & White’ Plants cooled for 6 weeks at 41 °F Juvenile (Vernalized as a 128-cell plug) 6 weeks bulking from 128-cell plug Short daysLong days

13. Juvenility (plant size) Photoperiod (day length) Vernalization (cold treatment) Dormancy sequence Hormones (Ethylene) Outline What plant is this? (Hint: Sold for the holidays)

14. “Biological” photoperiod during the year

15. Definition of Flowering Botanical definition Horticultural definition

16. Types of Photoperiod Responses Day-neutral plants (DNP) Short-day plants (SDP) Long-day plants (LDP) Other responses Schlumbergera (Thanksgiving cactus) is a short day plant

17. Types of Responses Facultative (Quantitative) response –Facultative SDP –Facultative LDP Obligate (Qualitative) response –Obligate SDP –Obligate LDP

18. Plants in Temperate Climates DNP = no response to long days Facultative LDP = long days accelerate (but are not required) for flowering Obligate LDP = long days are required for flowering

19. Day-Neutral Plant

20. Short-Day Plant Short days Pennisetum glaucum ‘Purple Baron’ 8 weeks forcing at 20 °C Long days Long days +HPS

21. Experiments have shown that the term short-day is something of a misnomer; the cocklebur requires a sufficiently long night for flower induction. For example, cocklebur will flower only if exposed to darkness for at least 8.5 hours – the critical photoperiod. Interruption of an otherwise long night by red light (660 nm) is particularly effective and prevents flowering, unless it is followed by irradiation with far- red (730 nm) light. Photoperiodism in Short-day Plants

22. Obligate Long-Day Plant Short days Stipa tenuissima 10 weeks forcing at 20 °C Long days Long days +HPS

23. Obligate Long-Day Plant

24. Critical Photoperiod That photoperiod above or below which induces a population of plants into flower completely, rapidly, and uniformly.

25. Facultative Long-Day Plant

27. Intermediate-day or Short-long-day Plant

28. Ambiphotoperiodic Plant Sisyrinchium tinctorium ‘Puerto Yellow’ 10 weeks at 20 o C under photoperiods (h): 10 12 13 14 15 16 24 4-h NI

29. When natural photoperiods are short, long days can be created by providing electrical lighting. Factors that need to be considered for photoperiodic lighting include: the timing and duration of light delivery the light intensity provided the type of lamp used Creating Long Days

30. Long-day Lighting Strategies Night interruption (NI) Predawn lighting Day-extension lighting Continuous (24 h) lighting

31. Simple installation of incandescent lamps for photoperiodic lighting

32. 7:00 am1:00 pm7:00 pm1:00 am7:00 am 12 hours

33. Flowering of Asclepias tuberosa with different long-day lighting strategies

34. Effect of Night Interruption Duration 10 percent lighting program (lights on for 6 minutes, off for 54 minutes) 20 percent lighting program (lights on for 6 minutes, off for 24 minutes)

35. Night-break lamps can be cycled on for 6 minutes and off for 24 minutes to reduce costs and electrical load. This is termed “cyclical lighting”. Cyclical night-break lighting is mainly used for short-day plants, and is sometimes effective for long-day plants. Continuous night-break lighting is usually applied to long- day plants as “insurance” for a strong response. Night Interruption Lighting

36. Cyclic Lighting BeamflickerIncandescent lamps

37. High-Pressure Sodium Lamps on Moving Boom

38. Effect of Night Interruption Intensity

40. Plants must have attained the “capacity to flower” to be induced to flower (juvenility) Newly mature leaves are most capable of being induced to flower In most species, repeated favorable photoperiods (cycles) are required for flowering In most species, once a plant has initiated flowers, they continue to develop to anthesis even when under an unfavorable photoperiod Photoperiodism Generalities

41. Photoperiod is measured in the leaf, then some signal is transmitted to the shoot apex and acts upon the meristem “Florigen” - A graft-transmissable compound - Moves through the phloem - Generated in the leaf of one species that can be grafted onto another species and initiate flowering. Photoperiodism Generalities

42. Juvenility (plant size) Photoperiod (day length) Vernalization (cold treatment) Hormones (Ethylene) Outline What plant is this?

43. Vernalization Response categories Effective cooling temperatures Duration of cold treatment required Facilities to provide cold treatment Easter Lily (Lilium longiflorum) has a vernalization requirement

44. Cold Treatment (Vernalization) Cold treatment beneficial or required –Facultative (quantitative) cold response –Obligate (qualitative) cold response

45. Effective Temperatures Range from 28 to 55 °F (-2.5 to 12 °C) 41°F (5 °C) is recommended Temperatures below freezing can be used, but avoid temperatures below 28°F (-2°C)

46. Duration Varies by species In some instances, as little as 2 to 3 weeks is long enough to provide beneficial effects of cold. Generally 6 to 10 weeks of cold is adequate for most perennial species tested

47. Delivering Cold Treatment Cool seedlings or cuttings in the plug tray. Pot in finish container, grow for several weeks under short days (in the fall), and then cool plants. –Species with a juvenile phase

48. Delivering Cold Treatment In a cooler In a greenhouse Under a thermal blanket outdoors Purchase plugs that have been cooled

49. Delivering Cold Treatment

53. Vernalization Vernalization (for 6 weeks or more) improves flowering in many ways: more plants flower, flower count increases, and time to flower decreases. Thus, cold treatment is highly recommended.

54. Veronica spicata ‘Red Fox’ 6 weeks at 68 °F 2 weeks vernalization 28 32 37 41 46 50 55 59 64 68 Control Vernalization Temperature (°F)

55. Veronica spicata ‘Red Fox’ 6 weeks at 68 °F 4 weeks vernalization 28 32 37 41 46 50 55 59 64 68 Control Vernalization Temperature (°F)

56. Veronica spicata ‘Red Fox’ 6 weeks at 68 °F 6 weeks vernalization 28 32 37 41 46 50 55 59 64 68 Control Vernalization Temperature (°F)

57. Veronica spicata ‘Red Fox’ 6 weeks at 68 °F 8 weeks vernalization 28 32 37 41 46 50 55 59 64 68 Control Vernalization Temperature (°F)

58. Achillea ‘Moonshine’ 6 Weeks Vernalization 6 Weeks Forcing at 20°C 28 32 37 41 46 50 55 59 64 68 Vernalization Temperature (°F)

59. Campanula ‘Birch Hybrid’ -2.5 0 2.5 5 7.5 10 12.5 15 17.5 20 Weeks of cooling 12 9 7 3 5 Temperature (ºC)

60. Miltoniopsis Augres ‘Trinity’ 52 °F57 °F63 °F68 °F73 °F 9-h photoperiod 8 weeks at 73 °F with 9-h pre-vernalization photoperiods Followed by 8 weeks at: 46 °F 0 70 100 40 10 0 Plants were subsequently forced at 68 to 73 o F under 16-h photoperiods

61. Phalaenopsis Miva Smartissimo × Canberra ‘450’ 12-h Photoperiod 20 Weeks Forcing at: (°F) 5768637379 Visible Inflorescence Percentage Flowering Percentage 010100 10 100 10 84 0 0

62. Juvenility (plant size) Photoperiod (day length) Vernalization (cold treatment) Hormones (Ethylene) Outline What plant is this? (Hint: It’s an epiphyte)

63. Hormones

64. Bromeliads flowering in Iguazu Falls National Park, Brazil

65. Information and photos presented in this lecture were generated by Researchers at Michigan State and Purdue Universities. Acknowledgments