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

Flower Induction in Flower Induction in the Floriculture the Floriculture IndustryIndustry

HRT 301HRT 301

Roberto G. Roberto G. LopezLopez

Purdue Purdue UniversityUniversity

• Juvenility (plant size)• Photoperiod (day length)• Vernalization (cold treatment)• Hormones (Ethylene)

Outline

What plant is this? (Hint: It’s not Arabidopsis!!)

Flowering Can Be Influenced By:

• Juvenility – plant size or maturity

• Environmental signals– Cold (vernalization)– Photoperiod (day length)– Dormancy sequence

• Hormones– Ethylene

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

Juvenility

A young stage of plant development in which plants from seed are not capable

of flowering

Juvenility

• Juvenile period of woody plants usually lasts

many years (Table 25.1 in text)

• For most herbaceous perennials usually less

than one year.

Plant Developmental Stages

Juvenile stage

Mature stage

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

Incomplete Vernalization of Perennials

Examples of Leaf Number Requirementsfor 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 name Age Requirements

Aquilegia ‘Origami Red & White’Plants cooled for 6 weeks at 41 °F

Juvenile (Vernalized as a 128-cell plug)

6 weeks bulkingfrom 128-cell plug

Short days Long days

• Juvenility (plant size)• Photoperiod (day length)• Vernalization (cold treatment)• Dormancy sequence• Hormones (Ethylene)

Outline

What plant is this? (Hint: Sold for the holidays)

“Biological” photoperiod during the year

Definition of Flowering

• Botanical definition

• Horticultural definition

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

Types of Responses

• Facultative (Quantitative) response– Facultative SDP– Facultative LDP

• Obligate (Qualitative) response– Obligate SDP– Obligate LDP

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

Day-Neutral Plant

Short-Day Plant

Shortdays

Pennisetum glaucum ‘Purple Baron’8 weeks forcing at 20 °C

Longdays

Longdays +HPS

• 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

Obligate Long-Day Plant

Shortdays

Stipa tenuissima10 weeks forcing at 20 °C

Longdays

Longdays +HPS

Obligate Long-Day Plant

Critical Photoperiod

• That photoperiod above or below which

induces a population of plants into flower

completely, rapidly, and uniformly.

Facultative Long-Day Plant

Intermediate-day or Short-long-day Plant

Ambiphotoperiodic Plant

Sisyrinchium tinctorium ‘Puerto Yellow’10 weeks at 20 oC under photoperiods (h):

10 12 13 14 15 16 24 4-h NI

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

Long-day Lighting Strategies

• Night interruption (NI)

• Predawn lighting

• Day-extension lighting

• Continuous (24 h) lighting

Simple installation of incandescent lamps for photoperiodic lighting

7:00 am 1:00 pm 7:00 pm 1:00 am 7:00 am

12 hours

12 hours

12 hours 12 hours

Flowering of Asclepias tuberosawith different long-day lighting strategies

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)

• 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

Cyclic Lighting

Beamflicker Incandescent lamps

High-Pressure Sodium Lamps on Moving Boom

Effect of Night Interruption Intensity

• 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

• 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


Outline

What plant is this?

Vernalization

• Response categories

• Effective cooling temperatures

• Duration of cold treatment required

• Facilities to provide cold treatment

Easter Lily (Lilium longiflorum) has a vernalization requirement

Cold Treatment (Vernalization)

• Cold treatment beneficial or required– Facultative (quantitative) cold response– Obligate (qualitative) cold response

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)

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

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


• In a cooler

• In a greenhouse

• Under a thermal blanket outdoors

• Purchase plugs that have been cooled

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.

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)



28 32 37 41 46 50 55 59 64 68 Control


Achillea ‘Moonshine’6 Weeks Vernalization

6 Weeks Forcing at 20°C

28 32 37 41 46 50 55 59 64 68


Campanula ‘Birch Hybrid’

-2.5 0 2.5 5 7.5 10 12.5 15 17.5 20W

eeks

of

cool

ing

12

9

7

3

5

Temperature (ºC)

Miltoniopsis Augres ‘Trinity’

52 °F 57 °F 63 °F 68 °F 73 °F

9-h photoperiod

8 weeks at 73 °F with 9-h pre-vernalization photoperiodsFollowed by 8 weeks at:

46 °F

0 70 100 40 10 0

Plants were subsequently forced at 68 to 73 oF under 16-h

photoperiods

Phalaenopsis Miva Smartissimo × Canberra ‘450’12-h Photoperiod

20 Weeks Forcing at: (°F)

57 68 63 73 79

Visible Inflorescence Percentage

Flowering Percentage0 10 100 100 10

100 100 100 100 10

84

0

0


Outline

What plant is this? (Hint: It’s an epiphyte)

Hormones

Bromeliads flowering in Iguazu Falls National Park, Brazil

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

Acknowledgments

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

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