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Agricultural Research & Education Center
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Bradenton AREC-Research Report BRA1982-14 September, 1982
RESPONSE OF LEAVES OF GERANIUM CULTIVARS TO VARIED INSOLATION
ASSOCIATED WITH NORTH OR SOUTH LOCATION IN PLANT BEDS
S. S. Woltz, Arthur W. Engelhard, and J. B. Jones1, 2
High quality foliage is important to most floral crops but has been found
especially important in geranium (3, 4, 5, 6, 7). Leaf quality of geranium responds
to quality, intensity and duration of illumination (1, 2, 5). Growers make every
effort to provide quality leaves with geranium floral products and can benefit from
physiologically oriented information on production of high quality leaves as well as
flowers. An experiment used in another study was found to be a source of informa-
tion on geranium foliage quality as a valuable adjunct.
Texture, thickness, coloration with anthocyanin, a red-purple pigment, and
zonation (ring pattern development) of geranium leaves were observed to respond
differentially to natural solar illumination variables associated with leaf location
on north versus south end of experimental plots in a polypropylene cloth house (38%
shade) at AREC-Bradenton during the time the sun was in southern skies. This
afforded an opportunity to collect data for leaves receiving 6,000 foot candles
(mid-day) of solar illumination (south end of beds) in contrast with leaves that
were shaded much of the day (2,000 foot candles mid-day, north end of beds). It was
felt that a quantitative characterization of leaf response obtained in this manner
could be helpful in quantifying the effects of shading upon foliar qualities of
Plants were set in beds in the cloth house at the AREC-Bradenton, September
24, 1981, primarily for a study of bacterial leaf spot disease. Beds were ferti-
lized with 4 lbs of 18-6-12 Osmocote per 72 foot bed. Irrigation was furnished as
required using three viaflow tubes per bed. Each plot consisted of 12 plants with
a randomized block design for cultivar distribution in four replicate blocks.
Observational notes were made on leaves December 17, 1981 and leaves were sampled
for lab work December 23, 1981. Shaded leaves were selected on the north and high
light intensity-exposed leaves were selected on the south.
Cultivars are arrayed in Table 1 in order of decreasing anathocyanin ratings
for leaves on the south ends of beds. The array according to indicated anthocyanin
was used to select 6 cultivars for laboratory analyses. Delta Queen and Ringo
Salmon had the highest ratings while Sprinter White had the least. Leaves on the
Professor of Plant Physiology, Professor of Plant Pathology and Assistant
Professor of Plant Pathology, respectively.
2The authors express their appreciation to Speedling Corporation, Sun City, FL
for providing geranium plants and to Pat Cox for valuable technical assistance.
north had much less anthocyanin than those on the south ends of beds. Leaf thick-
ness ratings in Table 1 follow the same trend as the anthocyanin data, namely,
more palpable thickness on the south end of the beds than on the north. The
rankings of cultivars for leaf thickness also followed the same trend as for the
anthocyanin. Mean values for anthocyanin and palpable leaf thickness differed
significantly for north-south orientation.
Cultivars were selected 3 from the top anthocyanin ratings and 3 from the
bottom for further analysis as presented in Table 2. Starch content and dry
weight of leaf disks were greater for south samples versus the north location
samples. Delta Queen and Sooner Red were heavier starch producers on the south
of the beds than on the north. The dryweight of leaf disks is greater for Delta
Queen, Ringo Salmon, and Sooner Red than for the other cultivars but not in all
cases with statistical significance.
Ratios for the north-south parameters to be associated with photosynthate
production were in all cases greater than one when calculated on a S:N basis.
This provides support for an observation that the quality of leaves on the north
end of the bed during the season when the sun is in the south, reflect lower
photosynthate accumulation in the north leaves. Export to these leaves from less
shaded leaves on the plant probably is significant and may differ between cultivars.
The characteristic zonal patterns of cultivars with zonation was observed to be
much weaker on the north end of the bed in a shaded location (shaded by other
leaves of the plant).
In summary, the observations reported indicate that higher sunlight illumi-
nation contributes to greater foliar anthocyanin (red-purple pigmentation), greater
palpable thickness of leaf, more starch and heavier leaf lamina as shown by leaf
disk dry weight (based on unit area). These observations support the need for
adequate space for quality plant production and provide information as to cultivar
response to solar illumination shade regimes. Highest floral quality of geraniums
is clearly benefited by adequate sunlight. Growers should not attempt production
under the handicap of poorly illuminated (sunlight) greenhouses and should avoid
such close spacing of plants that leaf quality is reduced by inadequate light levels.
As shown by the data in this report, leaf coloration and texture are adversely
affected by lack of adequate sunlight.
Table 1. Visible anthocyanin (purplish) pigmentation and palpable leaf thickness
rating on leaves of geranium cultivars.
Anthocyanin rating* I Leaf thickness rating**
Cultivar N*** S MEAN I N S MEAN
Delta Queen 3.0 9.5 6.3 I 2.0 8.5 5.3
Ringo Salmon 3.0 9.5 6.3 I 2.5 8.0 5.3
Sooner Red 1.8 9.0 5.4 I 2.3 8.3 5.3
Picasso 1.8 7.3 4.6 I 1.8 6.8 4.3
Rosita 1.3 6.5 3.9 I 1.5 7.5 4.5
Sprinter Salmon 1.8 6.5 4.2 I 2.0 7.5 4.8
Sprinter Scarlet 1.3 5.0 3.2 I 2.3 6.0 4.2
Red Express 1.0 2.3 1.7 I 1.8 5.0 3.4
Tara 1.0 2.3 1.7 I 2.3 6.5 4.4
Bright Eyes 1.0 1.3 1.2 I 1.5 5.5 3.5
Sprinter White 1.0 1.1 1.1 1 1.5 4.5 3.0
LSD, 5% level 1.5**** 1.5 1.1 1.1**** 1.1 0.8
*Anthocyanin red-purple pigmentation on a scale of l=least, 10=most.
**Leaf thickness rating, palpable thickness-texture on a scale of l=least, 10=most.
***N=leaves on north end of bed (shaded much of the day, 20% of full sunlight or
S=leaves on south end of bed (72% of full sunlight)
*I**The LSD applies to comparisons of any two numbers within or across N-S data.
Table 2. Starch content and unit area dry weight of geranium leaves.
(ppm fresh weight)
N S MEAN
Dry weight of leaf disks
N S MEAN
LSD, 5% level 4270* 4270* 3020 0.8* 0.8* 0.6
*The LSD applies to comparisons of any two numbers within or across N-S data.
r" + i tr -
1. Ahmedullah, M., W. J. Carpenter and H. L. Mitchell. 1963. Identification
of anthocyanidins in three cultivars of geranium (Pelargonium hortorum)
by chromatographic and spectrophotometric methods. Proc. Amer. Soc. Hort.
2. Craig, R. and D. E. Walker. 1963. The flowering of Pelargonium hortorum
Bailey seedlings as affected by cumulative solar energy. Proc. Amer. Soc.
Hort. Sci. 83:772-776.
3. Hasselkus, E. R. and G. E. Beck. 1963. Plant responses to light transmitted
into a fiberglass reinforced plastic greenhouse. Proc. Amer. Soc. Hort. Sci.
4. Kofranek, A. M. and 0. R. Lunt. 1969. A study of critical nutrient levels in
Pelargonium hortorum, cultivar 'Irene'. J. Amer. Soc. Hort. Sci. 94:204-207.
5. Masterlerz, J. W. 1977. The greenhouse environment. John Wiley & Sons. 629 p.
6. Payne, R. N. 1975. Optimizing phosphoric acid and chlormequat concentrations
for growing 'Sincerity' geranium under alkaline water conditions. HortSci.
7. White, J. W. 1970. Effects of Cycocel, moisture stress and pinching on growth
and flowering of F1 hybrid geraniums (Pelargonium x hortorum Bailey). J. Amer.
Soc. Hort. Sci. 95:546-550.