|
J. Raymond Kessler, Jr. and Gary
J. Keever
Inconsistencies
exist concerning the role of photoperiod and vernalization in
flowering of Shasta Daisy (Leucanthemum × superbum)
cultivars. In early studies, flowering was hastened by increased
day length in several cultivars. In later studies, cultivars
either were obligate long-day plants for flowering or required
vernalization to flower. Recent work with ‘Snow Lady’
showed that long days, but not vernalization, hastened flowering,
indicating a facultative response. This investigation was conducted
to determine the role of photoperiod and vernalization time on
growth and flowering of five Shasta Daisy cultivars.
METHODS
Transplants of ‘Becky’, ‘Silver Princess’,
‘Snow Cap’, ‘Snow Lady,’ and ‘Summer
Snowball’ Shasta Daisy in 72-celled flats were transplanted
to 6-inch pots containing Fafard #3 medium on October 10, 1997.
Plants were grown in a double-layer polyethylene-covered greenhouse
with a heating set point of 65oF and ventilation at
78oF. Fertilization of plants consisted of a weekly
application of 150 ppm nitrogen using 20-10-20. Plants were watered/fertilized
when the medium appeared dry, but before plants wilted.
On February 14, 1998, 54 plants of each cultivar were placed
in a walk-in cooler at 40oF for 3, 6, or 9 weeks and
were irrigated as needed with clear water. While in the cooler,
plants received nine hours of incandescent light (8:00 a.m. to
5:00 p.m.) at a minimum of 10 foot-candles. Eighteen control
plants of each cultivar were placed in a glass-covered greenhouse
with a heating set point of 64oF and ventilation at
76oF. Control plants and those removed from vernalization
were placed under either natural short days (SD) or long days
(LD) provided by incandescent light from 10:00 p.m. to 2:00 a.m.
Fertilization resumed when plants were removed from the cooler.
Beginning March 14, 1998, plants in short-day treatments received
black cloth from 5:00 p.m. to 8:00 a.m. daily until flower buds
opened. Data recorded at the time of first open flower was flower
date and shoot height. Quality rating (0-5) and flower shoot
number were recorded when plants had five open flowers.
RESULTS
All plants of ‘Becky’ flowered under LD, regardless
of vernalization time (VER), while none of the plants under SD
flowered (see table). Time to flower decreased as VER increased
under LD. Flower shoot number and quality rating increased with
increasing VER up to 9 weeks. Shoot height was greatest after
6 weeks VER under LD. ‘Becky’ showed an obligate requirement
for LD to flower, and plant growth characteristics and quality
were improved by at least 6 to 9 weeks of VER under LD.
|
Response of Three Leucanthemum ×
superbum Cultivars to Short or Long Photoperiods and Vernalization
Duration |
Photoperiod |
Vernalization
(weeks) |
Shoot
height (cm)1 |
Flower shoot number |
Market quality rating2 |
Days to flower |
Flowering
plants (%) |
|
|
‘Becky’ |
|
Short days |
0 |
-- |
-- |
-- |
-- |
0 |
|
|
3 |
-- |
-- |
-- |
-- |
0 |
|
|
6 |
-- |
-- |
-- |
-- |
0 |
|
|
9 |
-- |
-- |
-- |
-- |
0 |
|
|
12 |
-- |
-- |
-- |
-- |
0 |
|
Long days |
0 |
45.4 |
4.8 |
1.7 |
63 |
100 |
|
|
3 |
57.9 |
5.8 |
2.4 |
59 |
100 |
|
|
6 |
66.1 |
7.7 |
2.7 |
56 |
100 |
|
|
9 |
47.9 |
8.3 |
2.8 |
46 |
100 |
|
|
12 |
61.1 |
7.0 |
2.4 |
45 |
100 |
|
|
‘Silver Princess’ |
|
Short days |
0 |
-- |
-- |
-- |
-- |
0 |
|
|
3 |
21.5 |
2.6 |
1.9 |
57 |
90 |
|
|
6 |
22.5 |
5.0 |
2.4 |
57 |
78 |
|
|
9 |
21.8 |
6.3 |
2.4 |
46 |
78 |
|
|
12 |
22.0 |
6.7 |
2.3 |
40 |
100 |
|
Long days |
0 |
27.9 |
5.2 |
3.1 |
57 |
100 |
|
|
3 |
30.4 |
7.7 |
3.1 |
51 |
100 |
|
|
6 |
31.9 |
8.1 |
3.1 |
48 |
100 |
|
|
9 |
24.6 |
8.0 |
3.1 |
39 |
100 |
|
|
12 |
30.4 |
2.3 |
2.8 |
38 |
100 |
|
|
‘Snow Cap’ |
|
Short days |
0 |
15.7 |
1.3 |
0.0 |
75 |
33 |
|
|
3 |
-- |
-- |
-- |
-- |
0 |
|
|
6 |
17.3 |
2.0 |
1.3 |
61 |
89 |
|
|
9 |
16.3 |
4.0 |
2.0 |
53 |
22 |
|
|
12 |
17.3 |
5.7 |
2.7 |
47 |
100 |
|
Long days |
0 |
26.6 |
4.8 |
3.3 |
55 |
100 |
|
|
3 |
26.6 |
8.8 |
3.9 |
52 |
100 |
|
|
6 |
30.6 |
11.1 |
4.0 |
48 |
100 |
|
|
9 |
25.8 |
9.9 |
3.8 |
44 |
100 |
|
|
12 |
25.3 |
11.1 |
3.9 |
38 |
100 |
|
|
‘Snow Lady’ |
|
Short days |
0 |
15.6 |
6.9 |
2.3 |
60 |
78 |
|
|
3 |
20.6 |
7.9 |
2.4 |
58 |
78 |
|
|
6 |
19.7 |
7.3 |
3.0 |
56 |
78 |
|
|
9 |
16.5 |
8.1 |
2.5 |
44 |
89 |
|
|
12 |
18.3 |
8.4 |
2.9 |
41 |
100 |
|
Long days |
0 |
22.4 |
7.8 |
3.1 |
49 |
100 |
|
|
3 |
24.5 |
8.6 |
3.6 |
48 |
100 |
|
|
6 |
27.3 |
14.1 |
3.3 |
46 |
100 |
|
|
9 |
18.9 |
8.3 |
2.9 |
44 |
100 |
|
|
12 |
21.1 |
8.4 |
2.6 |
38 |
100 |
|
‘Summer Snowball’ |
|
Short days |
0 |
37.0 |
1.0 |
0.0 |
64 |
22 |
|
|
3 |
-- |
-- |
-- |
-- |
0 |
|
|
6 |
44.5 |
1.0 |
1.0 |
53 |
22 |
|
|
9 |
50.5 |
2.0 |
1.0 |
55 |
11 |
|
|
12 |
38.9 |
2.6 |
1.8 |
52 |
100 |
|
Long days |
0 |
53.2 |
4.0 |
2.4 |
65 |
100 |
|
|
3 |
64.8 |
6.9 |
2.8 |
61 |
100 |
|
|
6 |
66.7 |
7.9 |
2.7 |
59 |
100 |
|
|
9 |
62.1 |
4.4 |
2.1 |
52 |
100 |
|
|
12 |
52.7 |
7.1 |
2.4 |
52 |
100 |
1 English conversion 2.54
cm = 1 inch.
2 Quality rating: 0=no flowers, 1=very poor, unsalable;
2=poor, unsalable; 3=average, salable; 4=good, salable; 5=excellent,
salable. |
All plants of ‘Silver Princess’
and ‘Snow Cap’ flowered under LD while plants under
SD flowered 69% or 49%, respectively, regardless of VER (see
table). Flower shoot number generally increased and time to flower
decreased with increasing VER under LD and SD in both cultivars.
However, shoot height and market quality rating were unaffected
by VER or day length. ‘Silver Princess’ and ‘Snow
Cap’ showed a facultative requirement for LD to flower,
but the daylength requirement could be overcome by 12 weeks of
VER under SD where plants flowered 100%.
All plants of ‘Snow Lady’ and ‘Summer Snowball’
flowered under LD while plants under SD flowered 84% and 31%,
respectively, regardless of VER (see table). Shoot height, flower
shoot number, and market quality rating were unaffected by VER
under SD in both cultivars. Time to flower decreased with increasing
VER under SD in ‘Snow Lady’. Greatest shoot height,
flower shoot number, and market quality rating occurred after
3 or 6 weeks of VER under LD in both cultivars. Time to flower
decreased for both cultivars with increasing VER under LD in
both cultivars. Though there was no difference in quality rating
with increasing VER under SD or LD, quality rating under LD was
higher overall than under SD for both cultivars. ‘Snow Lady’
and ‘Summer Snowball’ showed a facultative requirement
for LD to flower, though a larger number of ‘Snow Lady’
plants flowered under SD. However, ‘Snow Lady’ plants
under LD flowered 7.8 days earlier, were 2 inches taller, and
had 3.6 more flowering shoots and a quality rating higher than
plants under SD. For both cultivars, the daylength requirement
could be overcome by 12 weeks of VER under SD where plants flowered
100%.
The Shasta Daisy cultivars tested in this study varied in response
to photoperiod and vernalization time. ‘Becky’ showed
an obligate requirement for LD to completely flower while ‘Silver
Princess’, ‘Snow Cap’, ‘Snow Lady’,
and ‘Summer Snowball’ showed a facultative response
with 100% of plants flowering under LD and varying percentages
flowering under SD. However all the facultative response cultivars
flowered 100% under SD and 12 weeks VER, indicating that long
VER periods may overcome the photoperiod requirement. For all
five cultivars, shoot height, flower shoot number, and market
quality rating increased while time to flower decreased with
increasing VER up to 6 weeks under LD. Therefore, LD and 6 weeks
VER would be needed to ensure rapid flowering and the highest
plant quality using these five cultivars.
|
