Artificial Plugging of the Stipe Base and Its Effects on Fresh Weight Change, Water Uptake and Vase Life of Detached Leatherleaf Fern Fronds

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University of Florida
Central Florida Research and Education Center - Apopka
CFREC-A Research Report, RH-92-20

R.J. Henny and W.C. Fooshee*

Postharvest wilt of leatherleaf fern fronds occurs when water loss from pinnae exceeds uptake by the stipe. Wilt may be a response to stipe plugging that prevents water from reaching pinnae; a failure of the stomates to close thereby allowing excessive water loss from the pinnae, or, a combination of both.

In the three experiments reported here, attempts to induce wilt were made by either leaving stipes suspended in containers with no water or by artificially plugging the stipe base. The object was to determine how fronds would react to extreme postharvest water stress and also to see if this stress could be alleviated using antitranspirants or leaf polishes.

Materials and Methods

In each of the experiments in this report, the test conditions were the same. Mature, dark green fronds were harvested from ground beds at this research center before 9:00 am and taken to an air-conditioned interior growth room where temperature was 80 ± 2°F with 100 foot-candles of illumination from fluorescent lights 12 hours per day. Frond stipes were cut with a single edge razor blade to 15 cm in length below the first pinule and then placed in 100 ml graduated cylinders with or without deionized water. Treatments were setup in a randomized block design with 10 replicates. Data included total water uptake, change in frond fresh weight and vase life.

The following three chemicals were tested for their antitranspirant properties: Cloud Cover (Adkar Inc., McAllen, TX) as a 33% solution; Pixie Sparkle (Teitelbaum Bros., Glenview, IL) as a 10% solution; and, Volck Oil (Chevron Chem. Co., Richmond, CA) as a 1.2% solution. Pixie Sparkle and Volck Oil are labeled as leaf polishes rather than as antitranspirants. Treated fronds were dipped in these solutions and the excess was shaken off, the stipe was wiped dry and then placed in cylinders.

Experiment 1: In this experiment (initiated April 8, 1991) fronds were artificially plugged by dipping the basal 1 cm of the stipe in lanolin. Six treatments were compared: 1) control, untreated fronds with stipes in deionized water; 2) stipe base plugged with lanolin, no water (i.e. stipe suspended in air in empty graduated cylinder); 3) lanolin plug, top of frond enclosed in plastic bag with moistened paper towels (i.e. bagged), no water; 4) lanolin plug, Cloud Cover dip, no water; 5) lanolin plug, Volck Oil dip no water; and 6) lanolin plug, Pixie Sparkle dip, no water. The purpose of the above treatments was to test the average vase life of this fern sample (treatment 1); induce wilt (treatment 2); prevent wilt by maintaining 100% relative humidity around fronds (treatment 3); or by applying antitranspirants (treatment 4); or leaf polishes (treatments 5-6).

Experiment 2: This experiment (initiated April 13, 1992) was similar to experiment 1 in that treatments to induce and/or prevent wilt were utilized. Treatments included were: 1) control, untreated fronds with stipes in deionized water; 2) stipe base plugged with lanolin, no water (i.e. stipe suspended in air in empty graduated cylinder); 3) lanolin plug, in water; 4) lanolin plug, no water; 5) lanolin plug, in water, bagged as in experiment 1; 6) lanolin plug, no water, bagged; 7) lanolin plug, Pixie Sparkle dip, no water; and 8) lanolin plug, Pixie Sparkle dip, in water.

Experiment 3: In this experiment (initiated May 6, 1992), treatments consisted of: 1) control frond, untreated fronds with stipes in deionized water; 2) control, no water (i.e. stipes suspended in air in empty graduated cylinder); 3) Volck Oil dip, in water; 4) Volck Oil dip, no water; 5) Pixie Sparkle dip, in water; and 6) Pixie Sparkle dip, no water.

Results

Experiment 1: Fronds held in water or plugged with lanolin but with tops kept at 100% relative humidity (bagged) had longer vase lives than any other treatments (Table 1). Fronds plugged with lanolin and suspended in air had the shortest vase life, surviving an average of 10.9 days. Pixie Sparkle increased vase life compared to the plugged control. Volck Oil and Cloud Cover had a positive, though nonsignificant, effect on vase life.

Experiment 2: In this test, vase life was shorter for fronds left out of water unless they were bagged or dipped in Pixie Sparkle (Table 2). Control fronds left out of water had an average vase life of 11.0 days which was not different from lanolin-plugged fronds (10.7 days) left out of water. All other treatments had longer vase lives. Control fronds in water, or bagged fronds in or out of water, lost less than 10% fresh weight over 14 days (Table 2). Greatest weight loss was observed with fronds suspended in air (-47.3%) or lanolin-dipped fronds in air (-45.2%). Fronds treated with Pixie Sparkle and left out of water lost significantly less (-20.4%) fresh weight (than the two control groups in air) indicating that it was effective in reducing transpiration water loss. Dipping stipe bases in lanolin did not completely eliminate water uptake as they averaged approximately 14 ml of water uptake during the experiment.

Experiment 3: As in the first two experiments, control fronds without water survived almost 10 days before wilting (Table 3). Volck Oil and Pixie Sparkle treatments did not increase vase life of fronds held without water. No treatments in water had any wilt and all survived longer than those without water. Fronds dipped in Volck Oil took up less water (82.9 ml) compared to Pixie Sparkle (136.0 ml) or controls (148.4 ml) but there was no difference in fresh weight change between the three treatments. There was less than a 1 % change in fresh weight in any treatment in water whereas the treatments with no available water lost between 41 and 44% fresh weight.

Discussion

The survival of detached leatherleaf fern fronds for 10+ days out of water before wilting is an indication that they can be very tolerant of water stress. In all three experiments reported here, the fern was harvested in April or May. The fact that this is not the 'wilt' season may mean fronds are more tolerant of water stress during this time of year. Repeating these tests in August and September is needed since previous research has shown that fronds emerging during June, July and August survived an average of only 2-8 days in water (2).

In these three experiments, fronds held in air with no available water could be differentiated from those in water after 2-3 days because they became a dull grey-green in color that was an early sign of desiccation, although the physical symptoms of wilt (curling and deformation of the frond) did not occur until later. The use of Pixie Sparkle significantly increased vase life in two of the three experiments, but had no significant effect in the other. Volck Oil had no effect on vase life, but reduced water uptake by approximately 45% compared to controls. Fronds with their tops maintained at 100% relative humidity did not wilt even when the stipe was out of water. These results indicate that wilt is apparently due to a lack of sufficient water supply to the frond which concurs with reported research on postharvest wilt of maidenhair fern (6). Since frond water loss is a factor leading to wilt, controlling water loss from detached fronds may be more important in preventing postharvest wilt than maintaining high levels of water uptake. This conclusion is supported by reports showing that the use of chemical treatment to increase water uptake by detached leatherleaf fern fronds has not been positively correlated to a significant increase in vase life (1,3,4,5).

Table 1. Effects of intentional plugging of the stipe base with lanolin, and addition of antitranspirants or leaf polishes on vase life and phytotoxicity of detached leatherleaf fern fronds.

^ZMean separation by Duncan's multiple range test; P = 0.05. Means followed by the same letter are not significantly different. Maximum possible vase life was 21 days.
^YPhytotoxicity symptoms of Pixie Sparkle included development of dark spots along pinnae edges; Volck Oil symptoms involved appearance of water-soaked areas within the pinnae.

Table 2. Effects of artificially plugging the stipe base with lanolin, maintaining the frond at 100% relative humidity, or addition of antitranspirants on percent change in fresh weight, total water uptake and vase life of detached leatherleaf fern fronds.

^ZMean separation by Duncan's multiple range test P = 0.05. Means followed by the same letter are not significantly different. Maximum possible vase life was 14 days.

Table 3. Effects of intentionally plugging the stipe base with lanolin, and addition of antitranspirants on total water uptake, percent change in fresh weight and vase life of detached leatherleaf fern fronds.

^zMean separation by Duncan's multiple range test; P = 0.05. Means followed by the same letter are not significantly different. Maximum possible vase life was 14 days.

*Professor, Environmental Horticulture and Senior Biologist, Central Florida Research and Education Center - Apopka, 2807 Binion Road, Apopka, FL 32703-8504, respectively.

Literature Cited

1. Nell, T.A., J.E. Barrett and R.H. Stamps. 1983. Water relations and frond curl of cut leatherleaf fern. J. Amer. Soc. Hort. Sci. 108(4):516-519.

2. Poole, R.T., C.A. Conover and R.H. Stamps. 1984. Vase life of leatherleaf fern harvested at various times of the year and at various frond ages. Proc. Fla. State Hort. Soc. 97:266-269.

3. Stamps, R.H. 1983. Effects of harvest time, postharvest dips, storage and frond physical characteristics on postharvest decline and water uptake of leatherleaf fern. HortScience 18(4):563. (Abstract).

4. Stamps. R.H. and C.R. Johnson. 1984. Vesicular-arbuscular mycorrhizal inoculation and fertilizer level affect yield, morphology, chlorophyll content, water uptake and vase life of leatherleaf fern fronds. Proc. Fla. State Hort. Soc. 97:264-266.

5. Stamps, R.H. and T.A. Nell. 1983. Storage, pulsing, holding solutions and holding solution pH affect solution uptake, weight change and vase life of cut leatherleaf fern fronds. Proc. Fla. State Hort. Soc. 96:304-306.

6. Van Doorn, W.G., D. Zagory and M.S. Reid. 1991. Role of ethylene and bacteria in vascular blockage of cut fronds from the fern Adiantum raddianum. Scientia Horticulturae 46:161-169.