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Flowering Physiology of Hatiora
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FLOWERING PHYSIOLOGY OF HAT/ORA

By

Charles Loyd Rohwer

A THESIS

Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE

Department of Horticulture

2002

ABSTRACT
FLOWERING PHYSIOLOGY OF HAT/ORA
By

Charles Loyd Rohwer

Hatiora, or Easter cactus, is a tropical epiphyte sold as a flowering potted
plant from mid-winter through spring. Plants can be induced to flower as early as
January, but the plants may be of poor horticultural quality. Flower induction for
crops sold in January must begin in October, but environmental conditions at this
time may not sufficiently fulfill the unique flower induction requirements for
Hatiora. Studies presented here examined the interactive effects of photoperiod,
light sum, and daylength before vernalization, and vernalization temperature,
vernalization light sum, and vernalization duration on Hatiora flowering. A four-
to six-week short-day treatment and elevated daily light integral (=10 pmol-m'z-s'
1) before six to eight weeks of vernalization at 7.5 to 12.5 °C were optimal for
uniform and rapid flowering. It was also discovered that vernalization in darkness
was effective and may be a useful method to extend the season. The effects on
flowering of propagation date and apical phylloclade removal were also studied.
Plants vegetatively propagated in April flowered better than plants propagated in
later months. Flowering was reduced by removal of apical phylloclades during

inductive treatments.

ACKNOWLEDGMENTS

My sincere thanks to Dr. Royal Heins for bringing me to MSU, questioning
everything, and using his experience and patience to teach me about floriculture
and research.

I also appreciate the valuable insights, ideas, and comments from Drs.
William Carlson and Jan Zeevaart. Dank u wel and tusind tak to Hans de Vries,
Jorn Hansson, and Kristian Madsen for their financial support and for spending
time to teach me what they know about cactus. Thanks also to the greenhouse
growers who support MSU floriculture, as what is accomplished in floriculture
research at MSU would not be possible without them.

A special thanks to the faculty, graduate students, staff, and visiting
scholars who made being here more fun. The following deserve special mention:
David Joeright, Mike Olrich, and the undergraduates who kept my experimental
units viable and the greenhouse working, and Marcus Duck, Carmela Rios,
Genhua Niu, Lee Ann Pramuk and Roberto Lopez for tolerating my spreading

habit and lame humor.

TABLE OF CONTENTS

LIST OF TABLES .................................................................................................. v

LIST OF FIGURES .............................................................................................. vi
SECTION I

LITERATURE REVIEW ........................................................................................ 1

Introduction ................................................................................................... 2

Nomenclature and Biogeography of Easter Cactus ...................................... 2

Production Methods for Hatiora gaertneri and H. xgraesen’ .......................... 6

Propagation ........................................................................................ 6

Nutrition, water, light, and temperature .............................................. 8

Leveling and spacing ....................................................................... 10

Plant growth regulators .................................................................... 11

Control of Flowering in Easter Cactus ......................................................... 13

Photoinduction ................................................................................. 13

Short-day phase ....................................................................... 14

Long-day phase (forcing) ......................................................... 15

Therrnoinduction .............................................................................. 15

Prevernalization period ............................................................ 16

Vernalization period ................................................................. 17

Long-day phase (forcing) ......................................................... 20

Civil Twilight Effects .................................................................................... 22

Other Short-Long-Day Plants ...................................................................... 26

Summary .................................................................................................... 28

Literature Cited ........................................................................................... 29
SECTION II

DAILY LIGHT INTEGRAL, PREVERNALIZATION PHOTOPERIOD, AND
VERNALIZATION TEMPERATURE AND DURATION CONTROL

F LOWERING OF EASTER CACTUS ......................................................... 35
Abstract ....................................................................................................... 37
Materials and Methods ................................................................................ 41
Results ........................................................................................................ 46
Discussion .................................................................................................. 50
Literature Cited ........................................................................................... 59

LIST OF TABLES

Table Page

SECTION II
1. Effect of short-day (SD) duration before vernalization and vernalization
duration and temperature on days to flower from the beginning of long days

in Hatiora gaertnen' ‘Jan’ and ‘Rood’. ........................................................... 65
2. Effects of prevernalization photoperiod and vernalization duration on flowering
of Hatiora. .................................................................................................... 66

3. Effects of propagation date and leveling date on buds per flowering apical
phylloclade and days to flower in flowering Hatiora gaertnen' ‘Jan’ and H.

xyraesen' ‘Evita’. .......................................................................................... 67
4. Flowering of Hatiora gaertnen’ ‘Jan' and H. xgraesen’ ‘Evita’ vernalized in a
dark cooler at 0, 5, 7.5, or 10 °C for 23 or 56 d. ........................................... 68

LIST OF FIGURES

Figure Page
SECTION I

1. Daylength in East Lansing, MI (42°45’ N) and the native range of Hatiora
(near 26° S) .................................................................................. 23

2. Twilight intensity as a function of solar angle for different weather
conditions ..................................................................................... 24

SECTION II

1. Flowering of Hatiora gaerfneri ‘Jan’ given short-day (10-h) or long-day (16-h)
treatment at high daily light integral (DLI) [ =12 mol-m'z-d‘1 photosynthetic
photon flux (PPF)] or low DLI (=45 moI-m' ~d") for six weeks followed by
vernalization at am or =4 mol-m'z-d'1 PPF and 7.5, 10, 12.5, 15, or 17.5 °c
for eight weeks ............................................................................................ 69

2. Effects of vernalization duration, temperature, and a 10-h short-day
prevernalization treatment on flowering uniformity in Hatiora gaertneri ‘Jan’
and ‘Rood’ ................................................................................................... 70

3. Buds per apical phylloclade on flowering Hatiora as a function of short-day
(10-hour) duration before vernalization and vernalization duration and
temperature. ............................................................................................... 71

4. Number of buds per apical phylloclade above the minimum (one per flowering
phylloclade) as a function of proportion of flowering phylloclades. ............. 72

5. Effect of propagation date and leveling treatment on flowering uniformity in
Hatiora gaertnen' ‘Jan’ and H. XQraesen' ‘Evita’. .......................................... 73

6. Hatiora xgraesen' increase in plant temperature above air temperature as a
function of photosynthetic photon flux. ........................................................ 74

vi

SECTION I

LITERATURE REVIEW

Introduction

Hatiora spp. are epiphytic cacti native to tropical Brazil. They are sold as
a flowering potted crop from March to May in the United States, and are one of
the few dual-photoperiod floriculture crops grown, although a vernalization-long-
day sequence is more often used to induce flowering than a short-llong-day
(SLD) sequence. Northern European producers grow upwards of 5 million pots
of Hatiora for sale beginning in mid-January but sometimes encounter difficulties
with nonuniforrnity of flowering at these early dates. This problem could be due
to a combination of insufficient temperature control and insufficiently short
photoperiods during the early stages of induction. Current taxonomic opinions,
production methods and their scientific basis, so-called natural photoperiods, and

a brief description of other SLD plants (SLDP) are presented here.

Nomenclature and Biogeography of Easter Cactus

Easter cacti (Hatiora), also called spring cacti, belong to a group of
epiphytic shrubs native to the southeastern Brazilian states of Parana and Santa
Catarina (Barthlott, 1983; Barthlott and Taylor, 1995). These cacti are members
of Cactaceae, tribe Rhipsalideae. Other genera in this tribe include Lepismium,
Pseudorhipsalis, Rhipsalis, and Schlumbergera (Barthlott, 1987; Barthlott and
Taylor, 1995).

Nomenclature of Easter cactus has changed in recent years. Growers
often still refer to the genus as Rhipsalidopsis or Rhipsalis, as cited in Hon‘us

Third (Bailey, 1976). Hatiora is now considered the correct genus for Easter

cactus, although Rhipsalidopsis is still considered an acceptable synonym
(Barthlott and Taylor, 1995). Rhipsalis is a separate genus generally containing
cacti that have more lateral flowers, which are typically whitish or yellow, unlike
the predominantly terminal Hatiora flowers, which are typically shades of pink,
orange, or red. Rhipsalis stems are more often terete than flat or angled,
although two subgenera, Phyllarthrorhipsalis and Epallagogonium, are lateral-
flowering Rhipsalis characterized by flat stems. Rhipsalis and Schlumbergera
are closely related to Hatiora (Barthlott, 1979; Barthlott and Taylor, 1995).

Most recently and more accurately, Easter cacti have been properly
labeled as species of Hatiora by botanical, scientific, and educational literature
(Barthlott and Taylor, 1995; Dole and Wilkins, 1999; Karle and Boyle, 1999).
Rhipsalidopsis is the subgenus including Hatiora. Therefore, referring to Easter
cactus as Rhipsalidopsis may be correct, but this nomenclature includes H.
epiphylloides, a nearly extinct relative. The two other species in the
Rhipsalidopsis subgenus are H. gaertneri and H. rosea (Barthlott and Taylor,

1 995).

Hybrids of H. gaen‘neri and H. rosea are labeled H. xyraesen'. Hatiora
gaen‘nen' and, more commonly, H. xgraeseri, are the typical Easter cacti
cultivated today (Barthlott, 1979; Boyle, 1990; Boyle, personal communication).
Hatiora naturally flowers in the spring (Bailey, 1976). Hatiora rosea typically
flowers later in the season than H. gaertnen' and may therefore be referred to as

Mother's Day cactus. Phylloclades of H. rosea are smaller than those of H.

gaertnen'. Flowers of H. rosea are usually smaller and show lighter pastel colors,
unlike the red flowers of H. gaertnen’ (Barthlott and Taylor, 1995).

The native habitat of Hatiora species is reflected in their flowering
requirements. Therrnoinduction requirements are greater for H. rosea than H.
gaertnen‘ or H. xgraesen' (Boyle, 1990), although many H. xgraesen' clones also
flower poorly without a vernalizing treatment (Boyle, 1995b). In its native
Brazilian habitat, H. gaertnen' is found at altitudes of 350 to 1300 m, whereas H.
rosea is native to 1000 to 2000 m (Barthlott and Taylor, 1995). Plants native to
the higher altitudes are likely to have a stronger vernalization requirement than
plants native to lower, more temperate altitudes, which seems to be the case for
H. rosea (Boyle, 1990; Wilkins and Rflnger, 1985).

Photoperiodic flowering of Hatiora is not as strong as flowering after a
vernalizing treatment, but some cultivars flower as SLDP at nonvemalizing
temperatures. The photoperiodic nature of these cacti may be a remnant of
photoperiodic flowering in ancestral species of desert cacti. The response to
vernalization may then be considered an evolutionary adaptation to higher
altitudes. This remnant short-day (SD) response is similar to the response of the
high-arctic SLD grasses Poa pratensis and Cerastium regelii (Heide, 1994). The
shortest civil daylength reached in the Panara and Santa Catarina region (lat.
326°S) is 11 h 28 min (Fig. 1, p. 22), and the most current research shows that
the critical SD photoperiod for Hatiora is between 11 and 12 h (Boyle, 1991).

Schlumbergera tmncata and S. xbuckleyi, the Thanksgiving and

Christmas cacti, respectively, are also popular potted members of the

Rhipsalideae tribe (Barthlott and Taylor, 1995). Schlumbergera flowers are
zygomorphic with a well-developed perianth tube. Vegetative stems of S.
truncata are noticeably more serrate-dentate than those of either 8. Xbuckleyi or
Hatiora. Schlumbergera lack dependence on long days (LD) for profuse
flowering, which is contrary to the actinomorphic flowers and LD requirement of
Hatiora (Boyle, 1991; Boyle et al., 1988; Dole and Wilkins, 1999). Optimum night
temperature for flower initiation in S. truncate is 15 to 20 °C, which is 5 to10 °C
higher than for induction in Hatiora (Boyle, 1991; Erwin et al., 1990; Peters and
RIJnger, 1971).

The Hatiora cultivars under experimentation at Michigan State University
include ‘Jan’ (large red flowers, pronounced and separated stigmatic lobes,
slightly elongated phylloclades, often reddish new growth), ‘Rood’ (small darker
red flowers, stigmatic lobes often closed and erect, more rounded phylloclades,
dark-red new growth), ‘Evita’ (pink flowers, phylloclades similar to those of ‘Jan’
except that new growth is often yellowish, poor branching and horizontal growth
habit under insufficient light), and ‘Rose’ (pink flowers, small phylloclades that are
easily separated from the mother plant, petals often twisted when open, prolific
branching). Taxonomic status of these cultivars is unclear because of extensive
breeding, but the following is estimated for each cultivar according to flower color
and structure, vegetative habit, and information provided by Thomas Boyle
(personal communication) and Han and Boyle (1996): ‘Jan’ and ‘Rood’ are H.

gaertnen’ (Regel) Barthlott, and ‘Evita’ and ‘Rose’ are H. xgraesen’ (Werdermann)

Barthlott. To the best knowledge of the author, no pure H. rosea (Lagerheim)

Barthlott plants were studied at Michigan State University.

Production Methods for Hatiora gaertneri and H. xgraeseli
Propagation

Hatiora phylloclades are easily harvested and rooted. Rather than a
single phylloclade’s being propagated, a series of adjoining phylloclades may be
propagated from cultivars with small phylloclades (Boyle, 1995b). Propagation
typically occurs from 8 to 12 months before sale (Boyle and Stimart, 1989).
Mature phylloclades are twisted off stock plants or plants that are leveled for
production purposes (described later). Ethylene and ethephon [(2-
chloroethyl)phosphonic acid] have been used experimentally to induce
phylloclade abscission for propagation. Ethephon concentrations 21250 uL-L‘1
caused phylloclade abscission (33 to 99%), and 22500 pL-L‘1 caused
phytotoxicity on abscised phylloclades (2 to 78%) (Han and Nobel, 1995). A 7-d
treatment with ethylene at 20 uL-L’1 also caused phylloclade abscission and
phytotoxicity on abscised pylloclades but did not affect new growth from remnant
phylloclades. The ethephon caused phytotoxicity on new aerial growth, whereas
the ethylene did not. Therefore, the acidity of the ethephon solution was
considered phytotoxic to new growth (Han and Nobel, 1995). Propagule root
length and number were also reduced by treatment with ethephon (Han and

Nobel, 1995).

Stock plants require no special treatment, but keeping them disease-free
is important. Stock plants are grown at 8 to 10 °C if possible to moderate their
vegetative growth (Hans de Vries, personal communication). When cuttings are
taken, phylloclades close to the soil should be avoided because they are more
likely to carry diseases (Dole and Wilkins, 1999). Mother plants may be treated
with a broad-spectrum fungicide, such as iprodine or chlorothalonil, 1 d before
cuttings are harvested to reduce losses caused by Fusan'um in storage or during
propagation (Hans de Vries, personal communication). It may be advantageous
to let fresh cuttings dry for about two weeks at 13°C to allow callus tissue to form.
Cuttings may be stored in a cooler at 13 °C and approximately 90% relative
humidity for up to six months (Hans de Vries and Jorn Hansson, personal
communication). Losses to disease also may be reduced by soaking the cuttings
immediately before planting in a 1.5% bleach solution (volume commercial
bleachzvolume water) for 15 minutes and then rinsing the pads in water (PKM,
personal communication). In addition, treatment of Hatiora propagules with
benomyl or chlorothalonil reduced infection of plants in Fusan'um-inoculated soil
(Mitchell, 1987).

Phylloclades are easily rooted under standard or relatively dry propagation
conditions. Two to three phylloclades are stuck in plug trays or directly in pots.
During rooting, medium temperature should be 21 to 26 °C, and watering may be
provided by intermittent mist or by hand. Excess water during rooting will limit

strong root growth. Hatiora may be propagated under natural daylengths. The

first flower bud or phylloclade to form on a cutting should be removed when it is
large enough to handle to promote branching.

Depending on rooting and growing temperature, plugs may be
transplanted after 6 to 16 weeks. Transplant-ready plugs should have two tiers
of pads, including the original (Boyle and Stimart, 1989; Hans de Vries, personal
communication). If plants are left in propagation trays too long, poor branching
may result (Jorn Hansson, personal communication). Larger plants should be

twisted to two tiers before transplant (Hans de Vries, personal communication).

Nutritioanater, IightLandL temperature

Media and nutrition requirements for Hatiora are not unique, but there are
distinctions worth mentioning. Well-drained peat-based medium is used
throughout production. Moderate fertilization (N at 125-200 ppm) should
commence when roots reach the side of the container. High Mg requirements

have been reported for Hatiora (Dole and Wilkins, 1999), and fertilizer may be

supplemented with MgSO4, which creates a darker green plant (Jom Hansson,

personal communication). However, twice the normal level of Mg (amount
unspecified) did not increase the number of flowers or the amount of dry matter
accumulation (Penningsfeld, 1972). The best dry-matter production was
achieved with fertility programs of twice the level of K (amount not specified) or
no added Zn (Penningsfeld, 1972). To slow vegetative growth, all fertilization

may be terminated one to two months before flower induction begins (Dole and

Wilkins, 1999) and may be eliminated during induction and forcing until buds are
visible (PKM, personal communication).

Micronutrient nutrition may require special attention. Media pH is
maintained above 5.7 (Nell, 1988) or 6 (Hans de Vries, personal communication)
to avoid micronutrient (Fe and Mn) toxicity, which manifests itself as discolored
phylloclade margins. Twice the normal level of B (amount unspecified)
significantly increased flower number and dry matter accumulation of Hatiora
when used in a full fertility regimen (Penningsfeld, 1972). Compared with
Fuschia thbn'da, Chrysanthemum indicum ‘Yellow Delaware’, and Pn'mula
obconica ‘Bayernblut’, Hatiora gaertnen' showed a relatively high accumulation of
Zn and Mo (>100 ppm and 5.2-6.3 ppm, respectively) without noticeable toxicity
(Penningsfeld, 1972). Plants grown in 50% peat and fertilized without
microelements showed no significant change in number of flowers or dry matter
accumulation compared with those grown under a control fertility program with
micronutrients added (Penningsfeld, 1972). Therefore, commercial producers
may choose not to add micronutrients (PKM, personal communication).

Plants should be allowed to dry slightly between waterings, but they
should not be allowed to wilt, especially during forcing (after vernalization).
Excess water will encourage weak, rapid vegetative growth (Nell, 1988; PKM,
personal communication).

Shade is usually necessary for growth in the summer. A maximum of
about 3500 foot-candles (700 umol-m'z-s’1) is recommended (Dole and Wilkins,

1999). High light coupled with high temperatures will cause phylloclades to

become chlorotic and abscise (personal observation; Dole and Wilkins, 1999).
Too little light causes weak and spindly branching and low bud count (Boyle and
Stimart, 1989; Nell, 1988).

Growing temperatures are moderate (18-24 °C) prior to induction.
Photoperiod and temperature interact during flower induction of Hatiora; this is
explained later under “Control of F lowering.” Growers of Hatiora typically cool
plants (S10 °C if possible) for 9 to 10 weeks, beginning in October or when
temperatures are cool enough. This procedure is followed by 16-hour LDs or
night-interruption (NI) lighting at 18 to 22 °C if natural daylengths are insufficient
for an adequate response (daylength during forcing is described later) (Dole and

Wilkins, 1999; PKM, personal communication).

Leveling and spacing

Leveling is done to increase branching and create a more uniform plant.

Plants are leveled (pinched or twisted) approximately six weeks before cold
treatments are begun, if necessary. A new tier of phylloclades will grow after
leveling, and when these reach =75% of their maximum size, induction may
begin (Boyle, 1997; Jorn Hansson, personal communication). Depending on the
growing temperature, one new phylloclade forms in approximately six weeks
under LD conditions. Plants are usually leveled to two to four phylloclades.
More tiers are left on cultivars with smaller phylloclades or on plants in larger

pots. It is important not to damage subtending phylloclades when leveling plants

10

because the areolar meristem is the location of new reproductive and vegetative
growth.

Plants may be grown pot to pot for the duration of the growing season.
Some growers choose to give plants 25% more space approximately four weeks
before beginning flower induction if space is available (Jorn Hansson, personal

communication). For a 4-inch pot, this spacing is from 97 pots/m2 to 77 pots/m2.

Mowm regulators

The use of plant growth regulators in Hatiora production systems is
limited, but the effects of gibberellic acid (GA3) and benzyladenine (BA) have
been researched. Data show that GA3 at 5 to 500 mg-L'1 applied to Hatiora
gaertnen’ reduced the percentage of apical phylloclades flowering, buds per
flowering phylloclade, and number of buds per plant in favor of new phylloclade
formation (Boyle et al., 1994). Application before or at the beginning of LDs
(during 803) was more detrimental to flowering than application after LD were
started. One application of GA at 5 mg-L‘1 hastened flower development by 5 d
when applied to 1- to 2-mm-long buds (Boyle et al., 1994). Explants grown in
medium supplemented with 0.3 to 289 uM GA3 (harvested after SD treatment for
flowering) also showed a reduced number of flower buds compared with
untreated explants (Boyle and Marcotrigiano, 1997).

Benzyladenine increases organ formation in Hatiora gaertnen'. It
increased the number of new phylloclades in vegetative plants or explants and

the number of flower buds in reproductive plants (Boyle, 1992; Boyle and

11

Marcotrigiano, 1997; Boyle et al., 1988). Application of BA (200-1000 mg-L") at
27, 37, or 47 d after planting had no influence on the number of apical
phylloclades on the plant at 316 d after planting, but there were a greater number
of tertiary (3°) phylloclades [propagated phylloclade = primary (1°)] in treated
plants (Boyle, 1992). Multiple applications of BA at 200 mg'L'1 increased the
number of secondary (2°) phylloclades more than single applications of higher
concentrations. Benzyladenine applied to three- or six-month-old plants more
successfully increased branching and the number of apical phylloclades than
application to recently rooted phylloclades (Boyle, 1992). Application of BA at
>50 mg-L‘1 to plants 12 d after forcing treatments were begun increased the
number of buds per plant (from 48 to 89 maximum), number of buds reaching
anthesis (from 45 to 71 maximum), number of buds per flowering phylloclade
(from 2.1 to 3.4 maximum), nonapical phylloclades flowering (from 1.3 to 1.9
maximum), and percentage of aborted buds (from 6 to 20% maximum) (Boyle,
1995a). Most aborted buds were reported to be small (<1 cm). Benzyladenine
did not increase the percentage of apical phylloclades flowering, and BA at 10
mg-L'1 had little effect (Boyle, 1995a). Abortion of flower buds on BA-treated
plants was not reduced with silver thiosulfate treatment (Boyle et al., 1988).
Silver thiosulfate (2 mM) was shown to decrease bud abscission in plants with
small buds (<2.6 cm) or medium buds when applied one week before exposure

to ethylene (0.5 pL-L").

12

CLntrol of Flowering in Easter Cactus
Botanically, Easter cacti are short-long-day plants (SLDPs) for flowering
(Dole and Wilkins, 1999; Riinger, 1960). Using photoperiod to control flowering
is termed photoinduction. The SD phase of induction may be substituted with a
cold treatment (Boyle, 1991; Boyle and Stimart, 1989; Dole and Wilkins, 1999), a
process called thermoinduction. Photoinduction, although useful for breeding

purposes, is generally weaker than thennoinduction.

Photointhion

Easter cactus is considered an SLDP for flowering at 15 to 20 °C (Boyle,
1991; Boyle et al., 1988; Dole and Wilkins, 1999; Peters and Rflnger, 1971
Ranger, 1960). Hatiora gaertnen' “Crimson Giant’ given two, four, six, or eight
weeks of SDs (starting 11 Sept.) followed by 14-h LDs at 18 °C night temperature
responded with 100% of plants flowering, 1.3 to 1.7 buds per flowering apical
phylloclade (BPFAP), and 71 to 81% of apical phylloclades flowering (Boyle et
al., 1988). Plants grown first under LDs and then SDs flowered, with a maximum
of 80% of plants flowering, 1.0 BPFAP, and 32% of apical phylloclades flowering.
Continual SDs did not produce flowering plants (Boyle et al., 1988). Continual
LDs created the longest time to flower (89 d from the start of LDs) and the most
intermediate levels of BPFAP and percentage of apical phylloclades flowering
(PAPF) (Boyle et al., 1988). Previous experiments with H. gaertnen‘ showed no
substantial flowering for plants given 80 d of 8-h SDs followed by 16-h LDs at 2
20 °C (Peters and Riinger, 1971), indicating inhibition of flowering at

temperatures 2 20 °C.

13

Photoinduced H. xgraesen’ and H. rosea may flower more poorly than H.
gaertnen'. There was no substantial flowering at up to 90 d of 9-h SDs followed
by 15-h LDs for H. xgraesen‘ grown continually at 220 °C (Riinger, 1960), but
again this result may have been caused by high-temperature inhibition. Some
cultivars of H. rosea and H. xgraesen' flowered poorly or not at all following six
weeks of 8-h SDs followed by 14-h LDs at 18 °C night temperatures, while 100%
of H. gaertnen' ‘Crimson Giant’ grown under the same conditions flowered,
although with only 47% apical phylloclades flowering and 4.3 buds per plant

(Boyle, 1995b).

Short-da y phase

A minimum of four weeks of SDs is desired for horticultural flowering of H.
gaertnen‘. For H. gaertnen’ ‘Crimson Giant’, increasing duration of SDs at 20/18
°C (day/night) from two to eight weeks increased the percentage of apical
phylloclades flowering, number of BPFAP, and number of buds per plant for SD
photoperiods of eight to 11 h, although days to flowering increased (from start of
SD treatment on 4 Dec.) (Boyle, 1991). Minimum days to flower and maximum
BPFAP and percent apical phylloclades flowering were statistically achieved
following a minimum of 4 weeks of SDs (Boyle et al., 1988).

The critical SD photoperiod for photoinduction of H. gaen‘nen’ is between
11 and 12 hours. Eight weeks of 12-h photoperiods produced plants that
averaged 58% apical phylloclades flowering, 1.1 BPFAP, and 16.2 buds per

plant. Plants given the same duration of 11-h photoperiods had 82% apical

14

phylloclades flowering, 1.3 BPFAP, and 30.8 buds per plant (Boyle, 1991).
Number of BPFAP was significantly higher following eight weeks of 8-h SD

(BPFAP = 1.5) than eight weeks of 11-h SDs (BPFAP = 1.3) (Boyle, 1991).

Long-day phase (forcing)

Photoinduced H. gaertnen’ ‘Crimson Giant” do not flower or flower poorly
under continual SD (Boyle et al., 1988). The same is true for H. xyraesen'
(Riinger, 1960). However, after a minimum of eight weeks of 805, plants grown
at photoperiods >12 h or given 4-h NI treatments (beginning 17 Jan.) flowered.
Maximum BPFAP and percent apical phyllcoaldes flowering (=2.5 and 99%,
respectively) were achieved with photoperiods 214 h or NI. Plants flowered 15 to
25 d faster at these photoperiods than at 12 h (Boyle et al., 1988). Therefore, the
critical photoperiod for the LD phase is considered to be between 12 and 14 h,
and NI is equally sufficient. Microscopic analysis of the areolar meristem
showed that flower primordia were not present at the beginning of LDs following

an SD treatment (Boyle et al., 1994).

Thermoinduction

Response to photoinduction vs. therrnoinduction is genotype dependent.
Although Hatiora will flower as an SLDP, maximum flowering is achieved by a
cool treatment (vernalization) to supplement or substitute for the SD phase
(Boyle, 1991; Boyle and Stimart, 1989; Dole and Wilkins, 1999). Hatiora

gaertnen‘ ‘Crimson Giant’ showed 91% apical phylloclades flowering after six

15

weeks of 10 °C (night temperatures) and natural daylengths (beginning 24 Nov.,
preceded by natural daylength conditions and followed by 14-h LD at 21/18 °C
day/night). The same cultivar showed 72% apical phylloclades flowering after 18
°C treatment (under natural daylengths beginning 24 Nov.) and similar forcing.
However, H. xgraesen' ‘Evita’ flowered with 72% and 18% apical phylloclades
flowering, and H. xgraesen’ ‘Red Pride’ flowered with 90% and 22% apical
phylloclades flowering after the same respective treatments (10 °C vs. 18 °C)
(Boyle, 1995). Hatiora rosea flowered weakly after 16 weeks of photoinduction
(33% of plants flowering, 3.2 buds per plant) but flowered much better after 16
weeks of thermoinduction at 10 °C (100% plants flowering, 110.1 buds per plant)

(Boyle, 1990).

Prevernalization pen'od

Environment during the prevernalization affects flowering in Hatiora.
Before vernalization, 50 d of 9-h SDs effectively promoted flowering (greater
percentage of apical phylloclades flowering) than 50 d of 15-h LDs when H.
XQraeserf were vernalized for 60 d at 5, 10, or 15 °C. This effect was especially
apparent if vernalization was at 15 °C. In addition, prevernalization was also
more effective at 15 °C than 25 °C (Riinger, 1960), possibly because of the
thermoinductive nature of 15 °C. Only 38% of plants given 25 °C
prevernalization under 15-h photoperiods and then vernalized at 10 °C flowered,
with only 16 to 18% apical phylloclades flowering. On the other hand, 95% of

plants flowered when prevernalization was at 25 °C under 9-h photoperiods, with

16

32 to 34% of apical phylloclades flowering. Plants were damaged if
prevernalization temperature was 25 °C followed by a vernalization temperature
of 5 °C, most likely because of the strong temperature change. These data
emphasize the importance of 803 before cooling if vernalization temperatures
are 215 °C. Maximum flowering (100% flowering, 63% of apical phylloclades
flowering) was achieved with a 50-d SD pretreatment at 15 °C followed by SD
vernalization at 10 °C for 60 d (Riinger, 1960).

Hatiora gaertnen’ benefited from SD pretreatment similarly to H xgraesen‘.
Plants had significantly more apical phylloclades with flowers (maximum 81%) if
they were given 30 SDs instead of 30 L05 (starting 13 Oct.) at 15 to 20 °C before
a 50- or 70-d vernalization at 15 °C. Optimum temperature of the SD-
pretreatment was 10 to 20 °C over the range of 10 to 30 °C (Peters and Ranger,

1971).

Vernalization period

Vernalization is the “acquisition or acceleration of the ability to flower by a
chilling treatment” (Chouard, 1960). This definition applies to the cold treatment
given to Hatiora, during which initiation occurs or signals that allow initiation and
evocation during the subsequent LD treatment are made. Temperatures below
14 to 15 °C are vernalizing for Hatiora.

Hatiora gaertnen’ ‘Crimson Giant’ all flowered when given zero to eight
weeks of 18 or 10 °C (night temperatures under natural daylength beginning 4

Dec.) followed by LDs. However, vernalization at 10 °C yielded a greater

17

percentage of apical phylloclades flowering than induction at 18 °C after two or
five weeks of vernalization. After vernalization at 10 °C for durations beyond four
weeks, BPFAP and number of buds per plant were higher (2.3 BPFAP and 49
buds per plant at eight weeks) than at 18 °C (1.7 BPFAP and 33 buds per plant)
(Boyle, 1991). Days to flowering from the beginning of inductive treatment (4
Dec.), percentage of apical phylloclades flowering, number of buds per plant, and
BPFAP all increased with increasing duration of induction at 10 or 18 °C (Boyle,
1991)

Photoperiod was generally unimportant when vernalization was 90 d at 10
°C for H. XQraesen'. Percentage of apical phylloclades flowering at 10 °C was
slightly higher, although still poor (<65%) and not statistically significant, when
photoperiod during the vernalization was continual 9-h SDs rather than 15-h LDs.
Vernalization at 10 °C was better than that at 15 °C for LD photoperiods (Ranger,
1960).

Hatiora gaertnen‘ may show a larger response to photoperiod during
vernalization than H. xgraesen'. Hatiora gaertnen‘ plants vernalized for 80 d at 10
°C under 8-h SD (beginning 22 Dec.) had 75% apical phylloclades flowering,
whereas plants vernalized under 16-h LDs at 10 °C had only 43% flowering
apical phylloclades (Peters and RiJnger, 1971). The effect of photoperiod during
vernalization was more apparent after 80 d at 14 °C (beginning 30 Sept), when
74% percentage of apical phylloclades flowered under SDs and only 39%

flowered under LD (Peters and Ranger, 1971).

18

Response to photoperiod during vernalization may vary between
temperature treatments, species, cultivars, and even experiments. There was no
effect of photoperiod at 10 °C for H. gaertnen‘ vernalized for 50, 70, or 90 d
beginning 11 Nov. (Peters and RiJnger, 1971). Increasing photoperiods from 10
h to 24 h at 15 °C decreased the percentage of apical phylloclades flowering for
these same durations. Short-day photoperiods (10-h) were especially beneficial
(when compared with photoperiods 212 h or 10 °C vernalization) at 70 d of 15 °C
vernalization. Plants from these SD treatments at 15 °C had 80 to 85% apical
phylloclades flowering, whereas at 10 °C and the same photoperiod (10-h), the
percentage of apical phylloclades flowering was =40 (Peters and RiJnger, 1971).
These results further illustrate the tremendous variation, even using the same
clones and with data presented in the same paper, in Easter cactus research.
Possible reasons for this variation, especially relating to natural photoperiods and
starting date for inductive treatments, will be discussed later under “Civil Twilight
Effects” (p. 23).

As with some other plants, Hatiora respond to night temperature during
vernalization. In Xanthr'um, Pen'lla, and Kalanchoe, supra- and suboptimal
temperatures during the dark cycle in 805 reduced the effectiveness of the SD
treatment (Lang, 1965). With Hatiora, supraoptimal temperature during the dark
period in vernalization reduces effectiveness of vernalization, which is shown in
plants vernalized under SD at various day/night temperature regimens. Hatiora
gaertnen' vernalized at 10/10 °C or 20/10 °C (day/night) and 8-h SDs flowered

with 76 or 72% apical phylloclades flowering, respectively (Peters and Ranger,

19

1971). Only 9% of plants given 20/15 °C and SDs flowered, and 9% of plants
given 20/10 °C and 16-h LDs flowered (Peters and Riinger, 1971). Plants grown
at 10/20 °C and LDs flowered, although poorly (91 % of plants flowering, 32% of
apical phylloclades flowering). No flowering at any night temperature or
photoperiod was seen at 25 or 30 °C (day temperature) (Peters and Rilnger,
1971). Therefore, day temperatures during vernalization may rise to 20 °C with
no ill effects, as long as night temperatures reach 10 °C for the duration of
vernalization and photoperiods are sufficiently short.

Light has been considered necessary during vernalization of Hatiora.
During cooling treatments, 2000 lux (=30 umol-m'z-s'I) for 8 hours (=0.86 mol-m‘
2-d") produced the maximum percentage of apical phylloclades flowering of H.
gaertnen' (76% after 80 d of cooling at 10 °C), although there was no statistical
difference between any light treatment from 1000 to 4000 lux. Continuous
darkness during cooling did not produce any flowering plants, and considerable
phylloclade damage and abscission can occur under constant darkness (Peters

and Riinger, 1971; personal observation).

Long-da y phase (forcing)

As with photoinduction, therrnoinduced H. gaertneri flower poorly if forced
under SD photoperiods (Boyle, 1991; Boyle et al., 1988; Peters and RiJnger,
1971). The same is true for the SLDPs Festuca pratensis and Dactylis glomerata
(Heide, 1987; Heide, 1988), and for Campanula medium under certain

treatments (Wellensiek, 1960). Hatiora xgraesen' thennoinduced with a 90-d

20

vernalization at 10 °C (beginning 15 Nov.) followed by forcing under 15-h LDs at
20 to 22 °C had a greater percentage of apical phylloclades flowering (45%) than
plants forced under 9-h SDs (36% apical phylloclades flowering) (Riinger, 1960).
Hatiora gaertnen' ‘Crimson Giant’ vernalized for eight weeks followed by LDs had
a similar number of buds, BPFAP, and PAPF as plants that were moved from
LDs to 8-h SDs after five weeks of forcing, suggesting a five-week minimum
period of LDs following vernalization. ‘Crimson Giant’ plants forced under
continual LDs flowered only 3 d earlier than plants moved to 80$ after five weeks
of LD (Boyle, 1991). ‘Crimson Giant’ plants forced under continual SDs require a
minimum of six weeks of vernalization, although only 5.6 buds formed per plant if
eight weeks of vernalization was followed by continual SDs (Boyle, 1991).

Hatiora are typically forced at 18 to 22 °C (Dole and Wilkins, 1999).
Raising the temperature after vernalization too quickly may cause the buds to
drop during forcing. Raising the temperature 2 to 3 °C per week to reduce bud
drop is typically recommended (PKM, personal communication; Nell, 1988), but
this practice may be beneficial because it lengthens the inductive period.

Experimentation has been performed on forcing under 10- to 24-h
photoperiods at 15, 20, and 25 °C. There were no differences in the percentage
of apical phylloclades flowering, days to flower, or BPFAP among H. gaertneri
vernalized at 15 °C for 70 d under naturally short photoperiods (beginning 20
Nov.) and forced at 10- to 24-h photoperiods at 15 °C for 30 (1 (followed by LDs at
20 to 22 °C until flowering). All apical phylloclades flowered with 2.4 to 2.8

BPFAP, and flowering took =66 days from the beginning of forcing. Percentage

21

apical phylloclades flowering decreased as forcing temperature increased to 20
°C (91-98%) or 25 °C (31-51%). Days to flower and buds per flowering
phylloclade also declined with increasing forcing temperature, to a minimum of
49 days (from beginning of forcing) and 1.4 buds at 25 °C (Peters and RiJnger,
1971). The advantage of forcing at 15 °C is that induction likely continues at this
temperature.

Light quantity during forcing may affect flowering following
thermoinduction. Data suggest that flowering in Campanula medium, another
SLDP, is influenced by light quantity during the LD forcing phase (Wellensiek,
1960). Light, C02 concentration, or both affect plant assimilation directly, and
assimilation before, during, and after inductive processes has been implicated in
the flowering response of many photoperiodic and vernalization-requiring plants
(Bodson and Bernier, 1985). Forcing of Hatiora may be accelerated by
increasing the light levels of an LD or NI treatment (PKM, personal
communication), which may be a result of increased plant temperature caused by

increased irradiance and therefore more rapid development.

Civil Twilight Effects

Civil daylength is the time it takes the sun to move from 6° below the
horizon before sunrise to 6° below the horizon after sunset (The Astronomical
Almanac, 2000). Civil daylength in East Lansing, Mich. (lat. 42°45’N) does not
decrease to 12 h in the autumn until approximately 15 Oct., with slight variations

caused by elevation and weather conditions (data interpolated from The

22

Daylength (h)

20

 

 

 

 

 

 

I
I
15
I
10
V /
é/ . j _ é/
0 1 L 1 1 L 1

 

 

June Aug. Oct.

Figure 1. Daylength in East Lansing, Mich. (lat. 42°45’N) and the

native range of Hatiora (near 26°S). The dark solid curve

represents civil daylength in East Lansing, the dashed curve is

actual daylength in East Lansing, and the thin solid curve is civil

daylength at lat. 26°S. A reference line is shown at 12 h (data

interpolated from The Astronomical Almanac, 2002).

Astronomical Almanac, 2000). Civil daylength is 56 minutes longer than actual

daylength in March and October and 71 minutes longer in mid-June (Fig. 1).

Most plants are able to perceive some part of civil twilight (the duration of

time when the sun is -0.85° to 6° below the horizon) for photoperiodic responses.

Light quantity plays a role in detection of the beginning and end of night (dark)

treatments in plants (Hughes et al., 1984; Cockshull, 1984). Minimum irradiance

causing a response in end-of-day treatments ranged from 0.02 to 4 umol-m‘z-s‘1

for Glycine, Pharbitis, and Xanthium (Cockshull, 1984).

23

 

 

 

 

1000 I r-
L
500-
400i
300-
200-
100-
50- Clear
40-
30* Fine
d I ll
3 20_ Middle clou 0 0
V
N Low cloud
2:
13 IO» j
a l-
3 g .
.5 I
a. 5 I .. 0 Clear orro- mo
If; . co Fine zrio-arlo “
.4 ’° f 0 Middle cioud 9IIO-IOIIO ‘
3 ~ , " 0 Low cloud 9IlO-IOIIO -
: O Roln
2 ~ ’ n | 0 Snow -
I
1' : r I.. J
I- I '§ .1
L I I :3 -I
r- | If -r
0.5 'f' ' O? '3, '-
o.I.- 5% "E .
>0.
0.3? 3: '5’, 1
l of. '
0.2- 0 I . E: "h .
I «:32: '6
| I I u I a
o_11-—_—-I_‘:1 .1 L 1 L 4 , g I] 1 j. 1 1 1

 

 

-ro-9 -e -7 -e -5‘-z.-;-a -2 -r o r 2 3 I. 5
Solar altitude H (deg)

Figure 2. Twilight intensity as a function of solar angle for different weather
conditions (Kishida, 1989).

24

Light during civil twilight is often strong enough to cause a photoperiodic
response. Luminous intensity of light (I, in lux) during twilight can be expressed
as a function of solar altitude (H, in degrees) and a variable 8 that ranges from —

5.15 for a sky obscured by low clouds to —7.43 for a clear sky (Fig. 2). This

relationship is defined by the equation I = e[(H—B)/O.87] from 0.2 to 50 lux
(Kishida, 1989). By this equation, plants with photoperiodic sensitivity to >1 lux
(0.02 umol-m‘2 s") of light will respond at solar altitudes of > -5.15° to 443°
under overcast or clear skies, respectively (Kishida, 1989). Therefore, in October
in East Lansing, Mich., the duration of light at intensities >1 Ix is 48 to 69 minutes
longer than actual daylength, depending on weather conditions. As stated, civil
daylength is 56 minutes longer than actual daylength in October. However, the
data to support these conclusions were recorded on the roof of a building, not in
a greenhouse. Internal greenhouse structures (or, in a natural Hatiora
environment, forest canopy) would increase the critical value of H for a
photoperiodic response, reducing perceived civil daylength.

Assuming a minimal schedule of eight weeks of induction followed by six
weeks of forcing to a marketable stage on 15 Jan., induction must begin on 9
Oct. On this date, daylength is 11.4 h (in East Lansing, Mich), but civil daylength
is approximately 12.3 h. A civil daylength of 11 h is not reached until
approximately 8 Nov. (The Astronomical Almanac, 2000). Therefore, if night
temperatures are insufficiently cold for a thermoinduction treatment (Peters and

Rt'Jnger, 1971), which may be possible in October, daylength is also likely to be

25

insufficiently short for a full photoinductive treatment (Boyle, 1991 ), and the

plants are not being induced to flower maximally by 15 Jan.

Other Short-Long-Day Plants

Campanula medium responds as an SLDP in much the same way as
Hatiora. Experiments have shown that C. medium may also be photoinduced,
but thermoinduction is stronger (Wellensiek, 1960). Campanula pyramidalis
requires photoperiods longer than 13 or 14 h after a vernalization treatment
(Zimmer, 1985). The juvenile phase, only after which flowering will occur, was
shorter for photoinduction than for thermoinduction, which suggests different
mechanisms for the two induction methods (Wellensiek, 1960). In addition, older
plants require less vernalization than younger, although still mature, plants
(Wellensiek, 1960; Wellensiek, 1985). More recently, two new C. medium
cultivars (‘Champion Blue' and “Champion Pink’) flower under continuous long
days without vernalization (Cavins and Dole, 2001).

Coreopsis grandiflora responds as an SLDP. Following SDs, horticultural
quality of the flowering plant is increased with an LD treatment (Ketellapper and
Barbaro, 1966; Runkle, 1996), as is the case with C. Ianceolata (Damann and
Lyons, 1993). Vernalization can replace the SD phase and create a more
uniform and prolific flowering response. Longer vernalization durations hastened
development and increased the percentage of plants flowering (Ketellapper and

Barbaro, 1966; Runkle, 1996). It was also suggested that 12.5-week-old plants

26

respond less strongly to vernalization than 21-week-old plants (Ketellapper and
Barbaro, 1966).

Plants from a New Zealand seed stock of Tn'folium repens responded as
SLDPs, with a minimum of 3 SDs to fulfill the SD requirement. One day of
continuous irriadiation saturated the LD requirement (Thomas, 1961).

Echeven'a hamisii behaves as an SLDP. Plants flowered only if the
photoperiod before LD was 12 h or shorter, and plants flowered after SD only if
the photoperiod was 12 h or longer. A minimum of 20 SDs is required for the
short-day phase, although longer durations are more beneficial for flowering
(Rtinger, 1962).

Some temperate grasses respond as SLDPs at temperatures above 15
°C. The responses are genotype and ecotype dependent (Heide, 1994). Ten or
more weeks below 18 °C during 8-h SDs, followed by LDs, were required for
heading in three Dactylis glomerata cultivars. These cultivars were sensitive to
photoperiod at vernalizing temperatures. Approximately 12 LD (24-h) cycles at
15 °C were necessary to satisfy the LD requirement (Heide, 1987).

Festuca has a more obligate requirement for cold temperatures than some
other SLD grasses, although many still respond to photoperiod during
vernalization. In F. pratensis, critical temperature for SD vernalization was 15 °C,
whereas critical temperature for long-day vernalization was 12 °C. Critical
photoperiod for the long-day phase was around 13 hours (Heide, 1988). Of three
SLD Fetsuca rubra varieties studied, one was photoperiod insensitive during

vernalization. The other two favored SDs during vernalization. Few F. rubra

27

plants flowered after vernalization at 15 °C, regardless of photoperiod (Heide,
1990b)

Similarly, Phleum alpinum requires temperatures below 15 °C for
adequate primary induction (vernalization). Short days (8-h) were substantially
more effective than LDs, especially at moderate (9 to 2 °C) vernalization
temperatures and short (6 to 9 week) vernalization durations. Increasing the
number of LD cycles after primary induction increased the number of

inflorescences, the culm height, and the development rate (Heide, 1990a).

Summary

Hatiora is one of the few mass-produced commercially profitable
floriculture cacti. Growing conditions and techniques are relatively simple and
space-efficient. Photoperiod and temperature treatments sufficient for flowering
are less straightforward. Physiologically significant photoperiod on any given day
is an objective function of the day of the year, latitude, plant characteristics,
weather conditions, and greenhouse superstructures. Variable response of
flowering between years within one Hatiora cultivar may be due to variable
annual photoperiods, weather conditions, and temperature during and before

induction.

28

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Raton, Fla.

33

Zimmer, K. 1985. Campanula pyramidalis, p. 127-129. In: A.H. Halevey(ed.).

CRC handbook of flowering, vol. 2. CRC Press, Boca Raton, Fla.

34

SECTION II

DAILY LIGHT INTEGRAL, PREVERNALIZATION PHOTOPERIOD, AND
VERNALIZATION TEMPERATURE AND DURATION CONTROL FLOWERING

OF EASTER CACTUS

35

Daily Light Integral, Prevernalization Photoperiod, and Vernalization
Temperature and Duration Control Flowering of Easter Cactus.

Charles L. Rohwer1 and Royal D. Heins2

Department of Horticulture, Michigan State University, East Lansing, MI 48824

Additional index words: Hatiora gaen‘nen', Hatiora xyraesen’, dark vernalization,

leveling, propagation, civil twilight

Received for publication . We gratefully acknowledge funding from J.

de Vries Potplantencultures bv., CB Cactus, Project GREEEN, and greenhouse

growers providing support for Michigan State University floriculture research.
Graduate Student. Current address: Dept. of Horticultural Science, Univ. of
Minnesota, St. Paul, MN 55108.

2Distinguished Professor, to whom reprint requests should be addressed (E-mail:
heins@msu.edu).

36

Abstract

Experiments were performed on Hatiora gaertnen' (Regel) Barthlott ‘Jan’
and ‘Rood’ and H. xgraesen' (Wedermann) Barthlott ‘Evita’ to determine their
flowering response to 1) daily light integral (DLI) before and during vernalization,
2) 0 to 6 weeks of short-day (SD) or long-day (LD) photoperiods before
vernalization at 10, 12.5, or 15 °C, 3) propagation from April to July, 4) timing of
leveling before or during inductive treatments, and 5) SD photoperiods before
vernalization under darkness at 0 to 10 °C. ‘Jan’ grown under elevated DLI
before vernalization and low DLI during vernalization flowered more prolifically
than plants grown under low DLI before vernalization or high DLI during
vernalization at 15 °C. Treatment with six weeks of SD photoperiods before
vernalization increased the number of buds per flowering phylloclade after
vernalization at 10 °C and increased flowering uniformity when vernalization
duration was insufficient or vernalization temperature was 12.5 or 15 °C. For
plants flowering in January, propagation the previous April produced better
flowering than propagation in May, June, or July. Removal of apical phylloclades
during prevernalization SD or during vernalization was deleterious to flowering.
Vernalization in the dark produced marginal flowering, but SD treatment prior to
vernalization increased the percentage of apical phylloclades flowering, buds per
flowering apical phylloclade and percentage of plants flowering after dark
vernalization. Collectively, the most uniform flowering in January occurred when
plants were exposed to a sequence of four to six weeks of SD, vernalization at

7.5 to 15 °C for eight weeks, then long-day forcing for seven weeks.

37

Easter cacti [Hatiora gaertneri (Regel) Barthlott and H. xgraesen'
(Wedennann) Barthlott] belong to a group of epiphytic cacti native to the
southeastern Brazilian states of Parana and Santa Catarina, near lat. 26°S
(Barthlott, 1983; Barthlott and Taylor, 1995). H. xgraesen‘ is a hybrid of H.
gaertnen’ and H. rosea (Barthlott and Taylor 1995). Flowering may be achieved
through photoperiod manipulation (photoinduction). Hatiora spp. are classified
as short-long—day plants (SLDP) for flowering from 15 to 20 °C (Boyle, 1991;
Boyle et al., 1988; Peters and Ranger, 1971; Rilnger, 1960).

Vernalization from 10 to 15 °C may substitute for the short-day (SD) phase
(thermoinduction), depending on cultivar. Therrnoinduction at 10 °C is optimal,
while 15 °C is marginal for H. xyraesen’, regardless of photoperiod (Riinger,
1960). For H. gaertnen', the optimum temperature for vernalization under SD is
10 to 15 °C; under long-day (LD) photoperiods, 10 °C is optimum (Peters and
RUnger, 1971). Flowering is generally stronger after thermoinduction than
photoinduction, especially in H. xgraesen' (Boyle, 1991; Boyle, 1995).

Extending the duration of inductive periods for Hatiora enhances
flowering. For example, increasing the duration of the SD phase (8 to 11-hour
photoperiods) of photoinduction from two to eight weeks increased the
percentage of apical phylloclades flowering (PAPF), number of buds per
flowering apical phylloclade (BPFAP), number of buds per plant, and flower
development rate for photoperiods of 8 to 11 h in H. gaertnen' ‘Crimson Giant’

(Boyle, 1991).

38

Treatment with SD before vernalization extends the inductive period and
improves flowering in Hatiora. This response to prevernalization SD has been
shown in other plants that respond to vernalization (Napp-Zinn, 1984). Hatiora
gaertneri given a 30-d SD treatment at 15 or 20 °C before a 70—d vernalization at
15 °C had a greater PAPF (78-81%) than plants grown under LD until
vernalization (62-63%) (Peters and Riinger, 1971). Hatiora XQraeseri given 50
SDs before vernalization for 60 d at 5 to 15 °C showed a larger proportion of
apical phylloclades flowering than plants given 50 L03 before vernalization
(Rt'inger, 1960). It was hypothesized in previous research that three Hatiora
cultivars had more flowers if artificial photoinduction began on 24 Nov. than if
photoinduction began on 21 Sept. because of natural 803 before 24 Nov. (Boyle,
1995).

Leveling, pinching, twisting, and pruning are synonyms for the removal of
apical phylloclades in Hatiora or the related Schlumbergera cacti to increase
uniformity, branching, and bud counts and to create a more compact plant. To
our knowledge, no research has been performed on timing of leveling for Hatiora.
Leveling the plants during vernalization is not recommended, and additional
cooling is suggested if plants are leveled during vernalization (Boyle, 1997; Nell,
1988). The closely related SD Schlumbergera cacti benefit from leveling 1 to 10
d after 805 are started (Boyle, 1997).

Vernalization in a cooler may provide means for extending the season or
cooling the plants when temperatures are insufficient for vernalization. Celery

(Apium graveolens L.), ajuga (Ajuga reptans L.), and carnation (Dianthus

39

caryophyllus L.) were insensitive to vernalization when no light was provided
(Eltzroth and Link, 1970; Ramin and Atherton, 1994), but flowering in carrot
(Daucus carota L.) was enhanced by vernalization in the dark compared to
vernalization under 12- to 20-hour photoperiods (Atherton et al., 1984). Previous
research indicates that vernalization of Hatiora in darkness is impractical (Peters
and Riinger, 1971), but prevernalization SDs may condition the plants for a dark
vernalization.

Easter cacti are sold as flowering potted plants from January to June in
northern Europe. Uniform flowering in January may be difficult to achieve, most
likely because of non-inductive temperature or photoperiod conditions during and
before the early stages of induction in early to mid-October (assuming eight
weeks of vernalization followed by six weeks under LDs until a marketable stage
is reached). The critical photoperiod for the SD phase of photoinduction in H.
gaertnen’ is 11 to 12 h (Boyle, 1991), and daylength including civil twilight on 1
Oct. is 12 h 41 min and 12 h 47 min at lat. 25°N and 55°N, respectively
(Astronomical Almanac, 2000). In early October, consistently achieving the 8 to
12 °C night temperatures recommended for thermoinduction (Boyle and Stimart,
1989; Neil, 1988) may be difficult.

Specific combinations of prevernalization SD treatment and vernalization
duration and temperature may increase reliability and uniformity of Easter cactus
flowering, especially for early-season crops. Reducing the total crop time through
later propagation would increase available space for growers in the spring and

reduce production costs. Vernalization of Hatiora in a cooler may save space

40

and allow extension of the market dates. Poor vernalization caused by
unpredictable weather in the fall and spring could be avoided by vernalizing in a
climate-controlled cooler. The objectives of this research were to 1) study the
effects of photoperiod before vernalization and daily light integral (DLI) before
and during vernalization, 2) identify combinations of SD treatments before
vernalization and vernalization treatments that increase uniformity and BPFAP,
3) observe differences in flowering after exposure to 2 different photoperiods of
SD pre-vernalization treatment, 4) identify propagation and leveling treatments
that increase uniformity and BPFAP, and 5) determine the effects on flowering of

SD treatment followed by vernalization in a cooler.

Materials and Methods

Phylloclades were harvested from vegetative cacti on 15 to 20 Apr. 2000
in Expt. 1, 15 to 20 April 2001 in Expts. 2,3, and 5, or as specified in Expt. 4.
Phylloclades were rooted under natural daylengths [Iat. 42°45’N, 13.4 h on 15
Apr. (Astronomical Almanac, 2000)] in a 70:30 (volzvol) peat:perlite mix in 55-cell
(23 cm3 per cell) plug trays. Air and bench temperature were set at 23 and 25
°C, respectively. Plants were grown under intermittent mist until transplant.
Rooted plugs were transplanted into 10.2-cm (0.46-L) plastic pots containing
70:30 peat:perlite (SureMix Perlite, Michigan Grower Products, Galesburg,
Mich.) Plants were irrigated with well water (containing 95, 34, and 29 mg-L‘1
Ca, Mg, and S, respectively) supplemented with water-soluble fertilizer to provide

the following (mg-L"): 125 N, 12 P, 125 K, 13 Ca, 1.0 Fe, B, and Mo, and 0.5 Mn,

41

Zn, and Cu (MSU Special; Greencare Fertilizers, Chicago, Ill.), acidified to a
titratable alkalinity of 140 mg°L'1 CaC03. Fertilization was terminated during
vernalization treatments and resumed during forcing.

Plants were maintained in a greenhouse under 16-h LDs from propagation
until the beginning of SD or vernalization treatments. In Expt. 1, LD were
provided until SD pre-vernalization or vernalization by pulling blackout cloth over
the plants from 17:00 to 08:00 HR and providing incandescent irradiation [(5
pmol-m'z-s'1 photosynthetic photon flux (PPF)] from 1700 to 0000 HR. LDs in
Expts. 2 through 5 were provided by high-pressure sodium (HPS) lamps (80
umoI-m’z's'1 photosynthetic photon flux) for 16 HR as needed from 0600 to 2200
to maintain a minimum of 80 umol-m'Z-s”. Pre-vernalization SD photoperiods
(10-h) were achieved by pulling blackout cloth over the plants from 1700 to 1800
HR and lighting (5 j.lmol-m'2-s'1 incandescent irradiation) from 1700 to 1800 HR.
Plants were grown under natural daylengths during vernalization in Expts. 2
through 5 and as described in Expt. 1. Long days during forcing were provided
by pulling blackout cloth over the plants from 1700 to 0800 HR and providing
incandescent irradiation (5 umol'm‘z-s") from 1700 to 0000 HR (16-h
photoperiod). Temperature in each greenhouse was measured in an aspirated
chamber every 10 s, and hourly averages were recorded by a CR-10 datalogger
(Campbell Scientific, Logan, Utah). Plants were grown at 21.5 :I: 2.7 °C (setpoint
= 20 °C) from propagation until vernalization and during forcing.

A randomized design was used in all experiments. Data were collected on

percentage of plants flowering, days from the beginning of forcing (after

42

vernalization) to visible anthers (time to flowering), number of apical phylloclades,
number of apical phylloclades with flowers, and number of buds. Percentage of
plants flowering, PAPF, BPFAP, and days to flowering were analyzed with single
degree-of-freedom X2 tests (Hoshmand, 1988) or a mixed model procedure
[PROC MIXED; SAS Institute Inc., Cary, NC. (Khattree and Naik, 1999)] after
transformation for increased normality, as described in each experiment.

Prevemalization DLI and photoperiod and vernalization DLI and
temperature (Expt. 1). Hatiora gaertnen’ ‘Jan’ were grown at 20 °C under 16-h
LDs or 10-h SDs (provided by incandescent lighting under blackout cloth from
1700 to 1800 HR) at high (=12 mol-m‘z-d", provided by supplementary HPS
lighting at 80 pmoI-m'z-s") or low (=4.5 mol'm'z-d'1) DLI for 6 weeks starting 19
Sept, 2000. The plants were then vernalized for 4 or 8 weeks at 7.5, 10, 12.5,
15, or 17.5 °c and high (=10 mol-m'Z-d") or low (a mol-m'Z-d") DLI. During
vernalization, plants were given 10 h of continuous supplementary irradiation
from 0700 to 1700 HR provided by HPS lamps at =170 (high DLI) or 80 (low DLI)
umolom'zos“. Plants given low DLI were grown under 50% shadecloth. All plants
were leveled 7 d after the beginning of vernalization to increase uniformity. After
vernalization, plants were forced under 16-h L0 as described above.

Statistical analyses were performed separately on the high- and low-

vernalization DLI treatments because of multiple significant interactions. Data for

PAPF were transformed ( arcsinJPAPF) prior to analysis. Days to flower data
were transformed (d‘z) and analyzed separately within each cultivar due to

multiple significant cultivar interactions.

43

Photoperiod before vemalization and vemalization duration and
temperature (Expt. 2). On 20 Sept. 2001, H. gaertnen' ‘Jan’ and ‘Rood’ were
moved into 10-h SDs as described in Expt. 1. More plants were moved into this
SD treatment on 4 Oct. and 18 Oct. On 1 Nov., plants from these SD treatments
(six, four, and two weeks of S03), along with plants from 16-h LDs (zero weeks
of SOS) were moved into greenhouses set at 10, 12.5, or 15 °C (actual
temperatures were 10.9 :t 1.8, 12.7 :I: 1.3, and 15.0 d: 2 °C, respectively) under
natural photoperiods [10 h 18 min on 1 Nov. at lat 42°45’N (Astronomical
Almanac, 2000)]. Apical phylloclades were removed 14 d after vernalization was
begun to increase plant uniformity. Vernalization treatments were for two, four,
six, or eight weeks, followed by forcing under 16-h LDs at 20 °C as described.

Average proportion of apical phylloclades flowering (PrAPF) on all plants
was multiplied by the percentage of plants flowering to illustrate flowering
uniformity. This flowering index ranged from 0 if no plants flowered to 100 if all
plants and all apical phylloclades flowered. The flowering index for each SD
treatment and vernalization duration combination was compared with the
maximum value in each cultivar and temperature by single degree-of-freedom X2
tests. Buds per flowering apical phylloclade (BPFAP) and time to flower were

transformed {[ln( number Of bUdS +1)] and (d'z), respectively}

number of flowering phylloclades

 

before analysis. There were seven plants per treatment.
Short-day pre-vemalization photoperiod (Expt. 3). On 22 Sept. or 6 Oct.,
2001, H. gaertnen' ‘Jan’ and H. x graesen' ‘Evita’ were moved to 10- or 11-h 803

provided by extending 9-h daylengths with incandescent lamps under blackout

44

cloth as described. On 3 Nov. (after six or four weeks of SDs), the plants were
moved to 12.5 °C and vernalized for four or eight weeks. Plants were leveled on
10 Nov. and forced as described above.

Percentage of plants flowering were analyzed by X2 analysis. Data on

PAPF, BPFAP, and time to flower were transformed {arcsinm , [In
(BPFAP+1)]’1 and (d4), respectively} before analysis. There were seven plants
per treatment.

Propagation and leveling date (Expt. 4). Hatiora gaertneri ‘Jan’ and H.
xgraesen' ‘Evita’ were propagated on 15 Apr., May, June, or July, 2001. These
plants were maintained under the propagation conditions described for
approximately six weeks. They were then moved to the 16-h LDs (from HPS
lamps) growing conditions described. Plants were moved to 10-h photoperiods
(as described in Expt. 1) for six weeks beginning on 22 Sept, vernalized for four
weeks at 10 °C beginning 3 Nov., and forced under 16-h LDs at 20 °C. Plants
were leveled on 6 Aug. (47 d before 80$), 2 Oct. (10 d after SDs started), 13
Nov. (10 d after vernalization started), or not at all. Plants propagated in July
were not leveled on 6 Aug.

The PrAPF on all plants and the percentage of plants flowering were
multiplied to determine flowering uniformity, as represented by a flowering index.
Each treatment value was compared with the maximum value within each main
effect (cultivar, propagation date, and leveling date) by single degree-of-freedom

12 tests. Buds per flowering apical phylloclade and days to flower were

45

transformed {[ln (BPFAP +1)]'1 and (d4), respectively} before analysis. There

were five plants per treatment.

SD treatment followed by vernalization in darkness in a cooler (Expt. 5).
Hatiora gaertneri ‘Jan’ and H. xyraesen’ ‘Evita’ were grown for six or three weeks
(starting 29 Nov. or 20 Dec., 2001, respectively) under 10-h SDs as described in
Expt. 1. On 10 Jan., these plants and plants given no SD treatment
(continuously under 16-h LD) were moved into unlit coolers set at 0, 2.5, 5, 7.5,
or 10 °C. Vernalization at these temperatures was for 23 or 56 d. Because of a
cooler malfunction, the final 7 d of the 56-d 10 °C treatment were carried out at
7.5 °C. Following vernalization, plants were forced as described above.

Percentage of plants flowering were analyzed by X2 analysis. Data for

PAPF and time to flower were transformed [arcsim/PAPF and (d’I), respectively]

before analysis. There were seven plants per treatment.

Results

Expt. 1. Temperatures from 7.5 to 15 °C and low DLI (=4 mol-m'z-d'1)
during the eight weeks of vernalization, combined with SD before vernalization,
produced the best flowering plants (Fig. 1). High DLI during vernalization
reduced the percentage of flowering plants (Fig. 1A vs. Fig. 1B), PAPF (Fig. 1C
vs. Fig. 1D), and BPFAP (Fig. 1E vs. Fig. 1F) when vernalization temperature
was 215 °C. The PAPF and buds per flowering apical phylloclade were higher on
average when plants were vernalized under low DLI compared to high DLI.

Plants grown under high DLI and SDs during prevernalization produced more

46

BPFAP than those pretreated with low DLI and LDs when plants were vernalized
under high DLI at 7.5 °C or low DLI at 7.5, 10, or 15 °C (Fig. 1E and 1F). Optimal
vernalization temperatures under the low vernalization DLI range from 7.5 to 15
°C (100% of plants flowering, >70% of apical phylloclades flowering, and >12
BPFAP), but the optimal range under the high vernalization DLI was 7.5 to 12.5
°C (286% of plants flowering, 260% of apical phylloclades flowering, and 21.2
BPFAP). Short-day treatment (10-h) before vernalization generally increased the
PAPF (Fig. 1C and 1D) and BPFAP (Fig. 1E and 1F) on plants were vernalized
at 7.5 to 12.5 °C.

Plants given prevernalization under LDs and vernalized for only four
weeks flowered poorly (58-73% plants flowering after 7.5 to 12.5 °C
vernalization) compared to plants given SD before 4 weeks of vernalization (93 to
100% of plants flowering after 7.5 to 12.5 °C treatment). A maximum of 83% of
apical phylloclades flowering and 1.45 BPFAP was recorded after 4 weeks of
vernalization for plants given a prevernalization treatment of high DLI and SDs
and then vernalized under low DLI at 7.5 °C. Because of the poorer flowering of
plants after four weeks of vernalization, the data for these treatments are not
shown here.

Expt. 2. Flowering uniformity increased as duration of prevernalization SD
treatment and vernalization increased (Fig. 2). The maximum flowering index
was typically found in plants given six weeks of $05 in combination with and
before eight weeks of vernalization. Vernalization at 10 or 12.5 °C for a duration

of eight weeks resulted in the greatest flowering uniformity; SD before cooling did

47

not significantly increase flowering uniformity on plants vernalized for eight weeks
at this duration and these temperatures. ‘Jan’ vernalized at 12.5 °C for eight
weeks with no prevernalizaion SDs flowered with uniformity similar to plants
given four or six weeks of SD before six weeks of vernalization at 12.5 °C.
Flowering index was low for plants vernalized at 15 °C, espeically for plants not
receiving an SD treatment. ‘Jan’ flowered more uniformly than ‘Rood’, especially
at 15 °C or at 12.5 °C with fewer than eight weeks of vernalization.

Number of BPFAP increased as the duration of vernalization increased at
all 3 temperatures (Fig. 3). The effect of SDs on BPFAP before vernalization
was significant only at 10 °C vernalization. Plants given 80$ for six weeks and
vernalized for six or eight weeks at 10 °C had =0.4 more BPFAP than if no SD
treatment was given before vernalization.

Treatments that resulted in a higher PrAPF also increased the number of
BPFAP (Fig. 4). The minimum number of buds per apical phylloclade (BPAP) is
equal to PrAPF. For example, if half of the apical phylloclades flower (PrAPF =
0.5) on a plant with 30 apical phylloclades, the minimum number of BPAP is also
0.5 (15/30). Therefore, subtracting PrAPF from BPAP will give the number of
buds per apical phylloclade above the minimum possible value. In general, the
number of buds above the minimum increased as PAPF increased, although
variability was larger at high PrAPF (Fig. 4).

Time to flower was influenced by vernalization duration and temperature
(Table 1). ‘Jan’ vernalized at 10 or 12.5 °C for six or eight weeks flowered on

average three days faster than plants vernalized at 15 °C for six or eight weeks.

48

‘Jan’ given two to six weeks of SDs prior to vernalization flowered an average of
two days faster than plants given no SDs before vernalization. Plants vernalized
at 10 °C for eight weeks flowered 11 to 21 d faster than plants vernalized at 15
°C for four weeks.

Expt. 3. All plants flowered after eight weeks of vernalization, with a
higher PAPF and more BPFAP than plants vernalized for four weeks (Table 2).
Plants given prevernalization 80$ for six weeks had a higher PAPF than plants
given four weeks of prevernalization, irrespective of photoperiod. Plants
vernalized for eight weeks flowered an average of 10 d faster than plants
vernalized for four weeks. Treatment with 10-h prevernalization photoperiod also
resulted in more rapid flowering than 11h.

Expt. 4. Plants propagated earlier in the year generally had higher
flowering uniformity, as shown by a larger flowering index (Fig. 5). Plants not
leveled or leveled before SDs flowered most uniformly. Uniformity was very low
for plants leveled during vernalization. ‘Jan’ flowered more uniformly than ‘Evita.’

The number of BPFAP was generally highest for plants propagated in
April (Table 3). ‘Evita’ had fewer buds per flowering phylloclade than ‘Jan’,
although the difference was not large. Number of buds per flowering phylloclade
was generally highest for plants leveled before SDs or not at all. Plants
propagated in July flowered later than plants propagated earlier for comparable
leveling treatments.

Expt. 5. Dark vernalization below 5 °C killed the plants (data not shown)

or did not substantially promote flowering (Table 4). ‘Jan’ had a higher PAPF

49

(48%) than ‘Evita’ (32%) and ‘Jan’ took an average of 2 d longer to flower. Short
days before vernalization increased the percentage of plants flowering in most
treatments, PAPF, and BPFAP. Vernalization temperature did not affect the
percentage of phylloclades flowering or BPFAP. Maximum flowering (100% of
plants flowering and 38 to 46% of apical phylloclades flowering) was achieved
with three weeks of SDs followed by 56 d of vernalization at 5 °C or six weeks of

SDs followed by 56 d of vernalization at 10 °C.

Discussion

Hatiora may flower as a SLDP, but flowering is enhanced by 10-15 °C
treatment during or instead of the SD phase (Boyle, 1991; Peters and Ranger,
1971; Riinger, 1960). Other plants with similar SLD flowering activity in which
SD may be replaced or enhanced by vernalization include Campanula medium
(Wellensiek, 1960; Wellensiek, 1985), Coreopsis grandflora and C. Ianceolata
(Damann and Lyons, 1993; Ketellapper and Barbaro, 1966; Runkle, 1996), and
Dactylis glomerata (Heide, 1987), Festuca rubra (Heide, 1990) and other
temperate grasses (Heide, 1994). The critical temperature for heading in
Festuca pratensis was 15 °C under SD and 12 °C under LD (followed by LD)
(Heide, 1988), which is very similar to Hatiora. Tn'folium repens (Thomas, 1961)
and Echeven'a harmsii (Ranger, 1962) also have shown SLD flowering
requirements.

As previously shown (Boyle, 1991; Peters and Rtinger, 1971; Riinger,

1960), extending the duration of inductive conditions, either with SD or cool

50

temperatures, enhanced flowering uniformity (Fig. 2). Marginal thermoinductive
conditions (15 °C) yielded poor flowering uniformity unless an extended SD
prevernalization treatment was given (Fig. 2). This illustrates the necessity of
SOS before vernalization under natural SD photoperiods if temperatures are
higher than those for optimum vernalization (2=14 °C). Short days provided with
blackout cloth before vernalization were provided in these experiments, but
natural SD photoperiods are likely to have similar beneficial effects (Boyle, 1995).

The response to vernalization is considered quantitative in many plants
(Lang, 1965), including Hatiora. Seventy-five percent of apical phylloclades
flowered on H. gaertneri vernalized for 80 d at 10 °C, and only 46% flowered on
plants vernalized for 60 d (Peters and Rt'Jnger, 1971). An increase in the
duration of vernalization at 10 °C from 50 to 70 d increased the percentage of
plants flowering from 75 to 96%, and increased the PAPF from 7.6 to 55% in H.
xgraesen' (Rt'lnger, 1960).

Flowering in Hatiora should be considered a quantitative response to
induction. If a plant flowers, it may flower on a single phylloclade or it may flower
on all phylloclades. If a phylloclade forms flowers, it may have one flower or it
may have numerous flowers. The horticultural quality of a plant improves as the
PAPF and the number of BPFAP increase. Botanical flowering describes a plant
with any number of flowers, while horticultural flowering describes a plant with
uniform flowering and numerous buds. Increased horticultural quality increases

the value of the plants.

51

Prevernalization SDs treatment under optimum vernalization conditions
were beneficial to flowering by increasing 1) flowering uniformity (Figs. 1 and 2),
2) the number of BPFAP (Fig. 3), and 3) the number of buds above the minimum
possible (Fig. 4). In Expt. 2, plants with more than 90% of apical phylloclades
flowering and more than two BPFAP (one more bud than the minimum, 37 plants
total) were vernalized for six or eight weeks at 10 or 12.5 °C, with one plant
vernalized at 15 °C (Fig. 4). The majority (62%) of these plants with favorable
horticultural flowering characteristics were also given four or six weeks of SDs
before vernalization, and 86% were given two, four, or six weeks of SOS.

It is likely that Hatiora responds to low PPF during part or all of civil
twilight, effectively extending natural daylengths beyond sunrise to sunset.
Photon fluence rates have been measured from =13 to 0.007 pmoI-m'z-s'1 during
civil twilight (the period starting in the morning or ending in the evening when the
sun reaches 6° below the horizon), depending on weather conditions (Kishida,
1989). Similar low fluence rates are thought to cause photoperiodic responses in
many plants (Hughes et al., 1984; Cockshull, 1984). If it is assumed that most
plants native to lower latitudes are more sensitive to civil twilight than plants from
higher latitudes, as is the case with Brassica (Tarakanov, 1998), then Hatiora
(native to lat. =26°S) is more sensitive to civil twilight than plants native to Europe
and the northern United States. Daylength including civil twilight does not reach
12 hours until approx. 16 October or 11 h until approximately 8 Nov. at lat.
42°45’N (East Lansing, Mich.) (Astronomical Almanac, 2000). Given that the

critical photoperiod for photoinduction is 11 to 12 h (Boyle, 1991), naturally

52

photoinductive conditions for Hatiora are probably not reached until mid-October
to early-November in East Lansing, Mich. If vernalization is to begin before this
time, i.e., for early-season crops, or if temperatures are insufficient for
vernalization, it is apparent that there are benefits of SD treatment before
vernalization to extend the induction period. The photoperiodic sensitivity of
Hatiora to low-fluence light and a more precise critical photoperiod need to be
established to determine when photoinduction naturally begins in the fall.

It has been recommended to level Hatiora before induction for uniformity
or a more compact shape if necessary (Boyle and Stimart, 1989; Neil, 1988),
allowing a new set of phylloclades to reach 75% maximum size before
vernalization begins (Boyle, 1997). Our data support the recommendation that
additional vernalization is necessary if plants are leveled during vernalization
(Nell, 1988). The low uniformity observed in ‘Jan’ and ‘Evita’ leveled during four
weeks of vernalization (Fig. 5) suggests that apical phylloclades respond to
vernalization more quickly than subtending phylloclades or that the process of
leveling significantly damages meristems in subtending phylloclades. Flower
primordia do not form on photoinduced H. gaertneri until after the SD phase of
photoinduction (Boyle et al., 1994), so leveling during vernalization probably does
not remove flower buds directly.

Hatiora gaertneri ‘Jan’ that were leveled 14 d after vernalization began
and were vernalized for eight weeks at 10 °C showed similar uniformity (Fig. 2) to
‘Jan’ leveled 47 d before pre-vernalization SDs were begun or not leveled at all

and vernalized for only four weeks (Fig. 5). It is therefore likely that fewer than

53

eight weeks of vernalization would be necessary in growing conditions similar
those in Expts. 1, 2, and 3 to achieve results similar to experiments 1, 2, and 3 if
the plants are not leveled or are leveled before SDs are begun.

Data presented here show that Hatiora will flower marginally if vernalized
in darkness (Table 4), although previous work showed that H. gaertneri failed to
flower if vernalized for 60 to 80 d in constant darkness at 10 °C, and =290
pmol-m'Z-s'1 during 80 d of vernalization created the highest PAPF over the
range of =144 to 575 pmol-m'z-s'1 (Peters and Rilnger, 1971). Pre-vernalizing
the plants with SDs increased the PAPF and BPFAP following dark vernalization
(Table 4). Increasing the prevernalization SDs and vernalization duration also
increased the percentage of plants flowering in most dark treatments.
Vernalization at 5, 7.5, and 10 °C were equally ineffective at creating
horticulturally desirable plants. Flowering after vernalization in a cooler was
generally poorer than after vernalization in a greenhouse (compare Table 4 with
other Tables and Figs.) Although many plants flowered, the horticultural quality
of all plants was low after vernalization in a cooler. Future research may show
that flowering of Hatiora vernalized in a cooler is improved by vernalization in the
light of a greenhouse before or after the dark vernalization period, or by providing
a minimum PPF in the cooler.

Poor flowering in coolers at 0-10 °C vernalization may be a result of
suboptimal temperatures in combination with no light. In previous research,
more H. gaertneri vernalized in a greenhouse for 60 to 80 d at 11 or 14 °C

flowered (33-100%) than plants vernalized in a greenhouse at 5 or 8 °C (0 to 8%)

54

(Peters and Rilnger, 1971). It may be possible that 5 to 10 °C are suboptimal for
dark vernalization of Hatiora, although ‘Jan’ vernalized in a greenhouse at 7.5 °C
under low DLI (=4 moI-m’z-d“, Fig. 1) flowered much better (100% flowering),
especially if they were grown under SDs before vernalization (93% apical
phylloclades flowering), than was previously reported for H. gaertneri at 5 or 8 °C
(Peters and Ranger, 1971). It was previously shown that H. xgraesen’ vernalized
at 5 °C flowered (RiJnger, 1960), but this treatment was preceded by 50 days of
15 °C, which may have vernalized the plants or preconditioned the plants for
vernalization at 5 °C. The differences between our research and previous
research are likely due to cultivar differences and experimental conditions,
including light intensity and photoperiod.

Some photoperiodic and day-neutral plants will flower in total darkness,
most often if sucrose is available (Lang, 1965). When given adequate glucose or
sucrose, Arabidopsis will complete morphogenesis and flowering in total
darkness (Araki and Komeda, 1993; Roldan et al., 1999), and some Brassica
napus L. and B. campestn‘s L. species will flower in total darkenss at 5 or 10 °C in
medium supplemented with sucrose (Inouye and Kuo, 1981). Hatiora do not
flower during vernalization, but sucrose availability during vernalization may
affect flowering.

High irradiance or availability of adequate nutrition and sucrose may
substitute for or act similarly to vernalization in some plants (Napp-Zinn, 1984;
Roldan et al., 1999), and flower initiation is profoundly influenced by availability of

stored assimilates in some plants (Bernier et al., 1993; Bodson and Bernier,

55

1985). Onion (Allium cepa L.) with high carbohydrate levels before vernalization
initiated flowers more rapidly after vernalization than plants with low
prevernalization levels of carbohydrates (Brewster, 1985). It has been suggested
that new vegetative growth in H. gaertneri is supported by translocation of carbon
from older tissue (Boyle, 1992). We have shown that high irradiance in
combination with SD before vernalization increases PAPF and BPFAP in Hatiora
(Fig. 1). Future research may show that flowering after vernalization in darkness
is improved by high irradiance before vernalization, after it, or both, thereby
increasing the accumulation of assimilates available for translocation during
initiation. In addition, our research and previous research showed that 305
before vernalization had beneficial effects on vernalization in a greenhouse or in
a dark cooler. Short days may act as a pre-conditioning treatment by favoring
accumulation of assimilates over growth processes.

Phylloclade temperature may increase beyond vernalizing temperatures
under high irradiance. A thermocouple placed in the apical areole of a single H.
xgraesen' plant recorded average hourly temperatures consistently above the
measured air temperature throughout an 8-d period in June 2002. The difference
between plant and air temperature increased as PPF increased, with a maximum
difference of 14.7 °C (Fig. 6). The shoot temperature of many cacti has been
recorded to be 215 °C above ambient air temperature because of the closed
stomata of crassulacean acid metabolism (CAM) plants during the daytime and
high heat storage capacity caused by succulence, among other factors (Nobel,

1988). Irradiation provided by HPS lamps increased shoot tip temperature of

56

vinca (Faust and Heins, 1997). In our experiments, high DLI during vernalization,
provided with HPS lamps, reduced all flowering responses at 15 °C compared
with $12.5 °C (Fig. 1). The results of Expt. 5 show that light is not an absolute
requirement during vernalization, and we have shown that supplemental light
during vernalization does not increase horticultural quality (Fig. 1). Therefore,
reducing the PPF intercepted by the plants during vernalization may improve the
response to vernalization by limiting the increase of plant temperature above air
temperature caused by increased solar gain.

Increased duration of vernalization and prevernalization SDs, to a lesser
extent, tended to hasten flower initiation, evocation, or development under LDs
(Tables 1, 2, and 4). Plants given six weeks of 10-h prevernalization SDs
flowered 4 d faster than plants given 11-h SDs (Table 2). These data show that
forcing time may be reduced by extended induction duration and sufficiently short
photoperiods.

Hatiora gaertneri and H. xgraesen' performed differently in our
experiments. Hatiora gaertneri ‘Jan’ flowered more uniformly or with a higher
PAPF than H. xgraeseri ‘Evita’ in Expt. 4 and 5 (Table 4, Fig. 5) and with more
BPFAP in Expt. 4 (Table 3). Hatiora xgraesen’ is an interspecific hybrid between
H. gaertneri and H. rosea (Barthlott and Taylor, 1995). Hatiora rosea is native to
higher altitudes than H. gaertneri (Barthlott and Taylor, 1995) and has a greater
requirement for vernalization than H. gaertneri (Boyle, 1990; Boyle, 1995). Three
late-flowering H. xgraesen' cultivars (‘5805’, ‘Phoenix,’ and ‘Capella’) also

flowered very poorly under non-ideal inductive conditions (data not presented).

57

The H. rosea parentage of ‘Evita’ helps explain the relatively weaker flowering of
‘Evita’ compared with that of ‘Jan’ and supports previous research indicating
strong genotype x environment interactions for flowering in Hatiora (Boyle, 1995).

The correct taxonomy for ‘Rood’ is unclear. lsozyme analysis suggests
that ‘Rood’ should be classified as H. gaertneri according to identity at nine loci
with an H. gaertneri accession. There was identity with H. rosea at only five of
the nine loci (O’Leary and Boyle, 1999). However, exact parentage of ‘Rood’ is
unknown. In Expt. 2, there was no difference between ‘Jan’ and ‘Rood’ in buds
per flowering phylloclade, but ‘Jan’ flowered more uniformly than ‘Rood,’
especially at 12.5 and 15 °C (Fig. 2), which suggests that ‘Rood’ may be H.
xgraesen' (possibly with a diluted H. rosea background), as reported before
lsozyme analysis (Han and Boyle, 1996). Exact taxonomy of ‘Jan’ is also
uncertain, but it is labeled here as H. gaertneri based on enhanced flowering
relative to the other cultivars and flower and phylloclade morphology (Bailey,
1976). However, our research suggests vernalization appears to be more
obligate for H. gaertneri ‘Jan’ than was previously noted for H. gaertneri ‘Crimson
Giant’ (Boyle, 1991)

Horticultural significance. These data, in combination with previous
research, confirm that uniform flowering of Hatiora requires a rather specific
sequence of environmental conditions and cultural practices. First, the flowering
response of older plants is greater than younger plants, even though Hatiora are
vegetatively propagated and juvenility should not be an issue. Short days for

four to six weeks followed by vernalization at 7.5 to 12.5 °C promote flower

58

induction. Flower development is then favored by forcing plants under LDs at
moderate temperatures of 17-20 °C for seven weeks. Sale of uniform flowering

plants requires 17-21 weeks from the start of the SD inductive process.

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64

Table 1. Effect of short-day (SD) duration before vernalization and vernalization duration
and temperature on days to flower from the beginning of long days in Hatiora gaertneri
‘Jan’ and ‘Rood’.

 

Vernalization temperature (°C)

 

 

 

 

Vernalization ‘Jan’ ‘Rood’
duration
(weeks) 10 12.5 15 10 12.5 15
0 weeks of SD
2 weeks of vernalization -’ - - - - -
4 weeks 59 59 -- 53 60 -
6 weeks 54 52 56 60 61 -
8 weeks 50 50 52 50 - -
2 weeks of SD
2 weeks --z - - - - -
4 weeks 55 57 63 - 71 73
6 weeks 53 52 53 56 57 59
8 weeks 47 46 52 52 53 57
4 weeks of SD
2 weeks --’ -- -- -- - --
4 weeks 56 56 56 59 64 65
6 weeks 52 50 52 56 58 60
8 weeks 48 45 51 51 54 58
6 weeks of SD
2 weeks -‘ - - - - -
4 weeks 57 56 57 61 59 66
6 weeks 50 51 53 56 57 60
8 weeks 46 48 51 53 53 57
Significance
Vernalization duration (VD) ** **
Short-day duration (SD) ** NS
Temperature (T) ** **
VD x PD NS NS
VD x T * NS
SD x T NS NS
VD x SD x T NS NS
NS, ‘

'"Nonsignificant or significant at P s 0.05 or 0.001, respectively.
2No flowering plants in this treatment.

65

Table 2. Effects of prevernalization photoperiod and vernalization duration on flowering of
Hatiora.

 

 

 

. . Apical Buds per
Waltz—aura Vernalization Plants phylloclades flowering
Duration PhOtOPGFIOd duration flowering flowering apical Days to
(week5) (hourS) (weeks) (%) (%)z phyllocladez flower”
4 10 4 86 20 1.2 58
8 100 57 1.7 47
11 4 71" 14 1.0 59
8 100 60 1.6 47
6 10 4 79" 33 1.1 54
8 100 67 1.6 45
11 4 54" 27 1.2 58
_ 8 100 58 1.5 49
Significance"
Vernalization duration (VD) ** ** **
Pre-vernalization duration (PD) * NS NS
Pre-vernalization photoperiod (PP) NS NS "
Cultivar (CV) NS NS NS
VD x CV NS * NS
PD x PP x CV * NS NS

 

"3' °' "Nonsignificant or significant at P s 0.05 or 0.001, respectively.

zData include flowering plants only.

yDays to flower from start of forcing (long days at 20 °C), flowering plants only.
"Significantly different from 100% flowering by x2 (a = 0.05, 1 df).
wNon-significant interactions (P > 0.05) are not shown.

66

Table 3. Effects of propagation date and leveling date on buds per flowering

apical phylloclade and days to flower in flowering Hatiora gaertneri ’Jan’ and H.
xgraeseri 'Evita’. Values in parentheses indicate the percentage of apical
phylloclades flowerflq in the treatment.

 

 

 

 

 

Buds per flowering Days to

Propagation date and apical phylloclade flowerz
leveling treatment ‘Jan’ ‘Evita' ‘Jan' ‘Evita’
April

None 1.5 (94) 1.4 (80) 56 52

47 d before 805W 1.6 (88) 1.2 (67) 56 55

10 d into SDs 1.2 (61) 1.4 (29) 56 54

10 d into vernalization 1.3 (10) 1.3 (33) 58 55
May

None 1.4 (78) 1.2 (44) 55 53

47 d before 805 1.3 (61) 1.1 (63) 56 53

10 d into 805 1.4 (33) 1.1 (24) 57 56

10 d into vernalization 1.0 (13) 1.0 (4) 60 61
June

None 1.5 (85) 1.2 (57) 53 54

47 d before SDs 1.4 (47) 1.3 (16) 58 55

10 d into SDs 1.2 (48) 1.0 (35) 57 58

10 d into vernalization 1.0 (3) 1.0 (4) 56 53
July

None 1.3 (18) 1.0 (12) 58 61

10 d into 805 1.3 (41) 1.0 (2) 56 67

10 d into vernalizationy 0.0 (0) 0.0 (0) -- --
Significance

Propagation date (P) * *

Leveling treatment (L) * NS

Cultivar (CV) * NS

P x L NS NS

P x cv NS NS

L x CV NS NS

P x L x CV NS NS

 

NS‘ 'Non-significant or significant at P s 0.05.
"Days to flower from the start of forcing (long days at 20 °C), flowering plants

only.

"No flowering plants in this treatment.
"Six-weeks of short-day (10-h) photOperiods given before vernalization.

67

Table 4. Flowering of Hatiora gaertneri ‘Jan’ and H. xgraesen‘ ‘Evita’ vernalized in a dark cooler at
0, 5, 7.5, or 10 °C for 23 or 56 d.

 

 

 

 

 

Vernalization Plants Apical Buds per
conditions and SD flowering phylloclades flowering apical Days to
duration (weeks)" (%) flowering (%)" pl'iyllocladey flower"
0 °C 31¢ ‘Evita’ gar; ‘Evita’ M ‘Evita’ ‘Jan’ ‘Evita'
23-d vernalization
0 weeks’SD 0W 0‘” 0 0 0.0 0.0 --" --
3 weeks’ SD 0W 0W 0 0 0.0 0.0 -- --
6 weeks’ SD 14‘" 29W 37 4 1.1 1.3 -- --
56-d vernalization
0 weeks’ SD 0w 0w 0 0 0.0 0.0 -- --
3 weeks’ SD 14W 0w 9 0 1.0 0.0 53 --
6 weeks’ SD 43‘” 0W 45 0 1.1 0.0 52 --
5 °C
23-d vernalization
0 weeks’SD 0w 14‘” 0 4 0.0 1.0 -- --
3 weeks’ SD 43‘” 14‘” 5 27 1.0 1.2 61 51
6 weeks’ SD 86 86 32 13 1 .1 1 .2 55 55
56-d vernalization
0 weeks’ SD 71W 17‘” 17 5 1.1 1.0 51 49
3 weeks’ SD 100 100 46 38 1.3 1.4 51 47
6 weeks’ SD 100 71W 54 35 1 4 1.2 51 46
7.5 °C
23-d vernalization
0 weeks’SD 29‘” 0w 7 0 1.0 0.0 57 -
3 weeks’ SD 86 57‘” 29 8 1.5 1.2 51 55
6 weeks’ SD 86 71‘" 43 17 1.3 1.2 52 52
56-d vernalization
0 weeks’ SD 86 14‘" 31 5 1.2 1.0 50 50
3 weeks’ SD 100 83 39 33 1.2 1.3 51 45
6 weeks’ SD 100 57W 39 32 1.2 1.2 49 48
10 °C
23-d vernalization
0 weeks’SD 0‘" 0W 0 0 0.0 0.0 -- --
3 weeks’ SD 100 57‘“ 36 18 1.2 1.1 54 55
6 weeks’ SD 100 86 43 18 1 .3 1 .3 52 52
56-d vernalization
0 weeks’ SD 17w 29W 20 1 1 1 .1 1.3 56 52
3 weeks’ SD 100 86 33 22 1.4 1.5 50 51
6 weeks’ SD 100 100 46 39 1.3 1.4 48 44
Significance
Cultivar (CV) " NS *
SD duration (SD) “ " "
Vernalization duration (VD) " NS **
Temperature (0“ NS NS NS
CV x SD NS NS NS
CV x VD NS NS *
SD x VD NS NS NS
CVxSDXVDXT NS NS *

 

"3 " "Non-significant or significant at P s 0.05 or 0.001, respectively.

"Plants were given zero, three, or six weeks of short days (SDs) before vernalization. No plants
flowered following 2.5 °C vernalization.

yData include flowering plants only.

"Days to flower from the start of forcing (long days at 20 °C), flowering plants only.

wSignificantly different from 100% flowering by X2 (a = 0.05. 1 df).

"No flowering plants or flowering took longer than 70 days.

“Temperature interactions that are not shown are not significant.

68

Plants flowering
(%)

flowering (%)

Apical phylloclades

Buds per flowering
apical phylloclade

PPF at 10 moI-m'"°d" PPF at 4 moI-m'"'d“
during vernalization during vernalization

 

  
 
 
 
 
 

(B)

 

«coo

 

100 r

 

V
U1
I

—e— 16-h high DLI
.. —o— 16-h low DLI
+ 10-h high DLI
—v— 10-h low DLI

50~
25—

 

 

 

 

100 L
75 ~
50 h
25 —

 

0
2.0 I

1.5 -
1.0 -
0.5 -

0.0 v
5.0 7.5 10.0 12.5 15.0 17.5 5.0 7.5 10.0 12.5 15.0 17.5

 

 

 

 

Vernalization temperature (°C)

Figure 1. Flowering of Hatiora gaertneri ‘Jan’ given short-day (10-
h) or long-day (16-h) treatment at high daily light integral (DLI)
[=12 mol-m"°'-d'1 photosynthetic photon flux, (PPF)] or low DLI
(=45 moI-m'2-d") for six weeks followed by vernalization at =10 or
=4 mol-d'1 PPF and 7.5, 10, 12.5, 15, or 17.5 °c for eight weeks.
Vertical bars represent :l:1 SE. Labeled treatments in graphs (A)
and (B) are significantly different from 100% flowering according to
single degree-of-freedom x" (or = 0.05). Lower case letters near
the symbols in graphs (C)—(F) indicate significant differences
within each temperature (P s 0.05; n s 7, depending on
percentage of plants flowering), and the absence of letters
indicates no statistical differences.

69

 

 

Short-day (10—h) duration

 

 

 

 

 

 

 

‘Jan’ ‘Rood’
., o
15°C . 15°C
,, - o»
2i O 0*
gr; 0’ f 2’ .
Q)
.. e-
3;: 12.5 °C @ 12.5 °C .
S4 0 G G»
{‘3
:2 ° 0 @i
Q)
:0’ Q 93 .
.9
3 610°C . 610°C .
.. - 0 el
2+ - . or
0i . 9 @l- f
2 4 6 8 2 4

 

Vernalization duration (weeks)

Figure 2. Effects of vernalization duration, temperature, and a
10-h short-day prevernalization treatment on flowering uniformity
in Hatiora gaertneri ‘Jan’ and ‘Rood’. Bubble size was
determined by (percentage of plants flowering) x (proportion of
apical phylloclades flowering). NS = not significantly different
from the labeled maximum within each temperature and cultivar
according to single degree-of-freedom X2 (on = 0.05). Treatments
without a bubble did not have flowering plants.

70

Buds er flowerin9
ap(Geigphylloclade

Buds per flowering
apical phylloclade

Buds per flowerinQ
apical phylloclade

 

Figure 3. Buds per apical phylloclade on flowering Hatiora as a
function of short-day (10-hour) duration before vernalization and

vernalization duration and temperature. Response is averaged over
cultivar (NS at a = 0.05).

71

 

Y = 1.14x2— 0.24x (R2 = 0.77)

 

 

 

Buds per apical phylloclade minus PrAPF

 

 

 

0.00 0.25 0.50 0.75 1.00
Proportion apical phylloclades flowering (PrAPF)

Figure 4. Number of buds per apical phylloclade above the
minimum (one per flowering phylloclade) as a function of
proportion of flowering phylloclades. All plants (flowering and
non-flowering) are included.

72

Leveling treatment

10d

after starting .

vernalization
10 d after

starting SD "

47 d before

starting SD "

none

10d

after starting .

vernalization
10 d after

starting SD ’
47 d before L

starting SD

none

 

 

3.1 a1

no

 

 

 

 

data
a1
0
’Evita'
3. a1 a1 a1
a a1 a
o . e 81
a1 no
. data
0‘ 1
April May June July

Propagation date

Figure 5. Effect of propagation date and leveling treatment on
flowering uniformity in Hatiora gaertneri ‘Jan’ and H. xgraesen'
‘Evita’. Bubble size was determined by (percentage of plants

flowering) x (proportion of apical phylloclades flowering). The
maximum value in each cultivar is labeled as a reference. SD

indicates short days

 

"Treatment value is significantly different from the maximum value

within the cultivar and column ()8. a = 0.05, 1 df).

1Treatment value is significantly different from the maximum value

73

within the cultivar and row (1 . ct = 0.05, 1 df).

 

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63
i5 0
CD

 

 

 

1 l L l l l i

 

200 400 600 800 1000 1200 1400

Photosynthetic photon flux (umoI-m'"-s'1)

Figure 6. Hatiora xgraesen‘ increase in plant temperature above air
temperature as a function of photosynthetic photon flux.

74

 

 

 

  
 

CH AN

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3129