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University of Florida
Central Florida Research and Education Center - Apopka
CFREC-A Research Report, RH-92-21
R.J. Henny and W.C. Fooshee*
Postharvest wilt of detached leatherleaf fern fronds is a complex problem that involves either excessive water loss from pinnae, insufficient water supply to pinnae via the stipe, or a combination of both. Considerable variation within leatherleaf fern experimental treatments is normal and has made study difficult. This variation has been attributed to a combination of environmental, cultural and post-harvest factors affecting occurrence of wilt (3). One consistent piece of data resulting from postharvest studies of leatherleaf fern is the plot of the water uptake curve. Water uptake declines in a logarithmic/exponential fashion during the first 5-7 days postharvest (4,5). Daily recutting of the stipe base significantly increased the amount of water uptake, although the curve shape remained similar, indicating some form of stipe blockage (2).
Studies of maidenhair fern (Adiantum raddianum) postharvest wilt showed that vascular occlusion of stipes occurred and was due solely to the presence of bacteria; i.e. increased vase life was always associated with lower bacterial counts (6). In the same report, it was found that adding 10 or 20 mg/liter of chlorine bleach to the holding solution resulted in vase life of 18.4 and 20.0 days respectively, compared to 3.4 days for untreated controls. Work with roses indicated that high bacterial levels in holding solutions were correlated with decreased water uptake (7). This effect was only observed at bacterial counts of 10(7) or 10(8) bacteria per ml or higher and counts of 3 x 109 bacteria per ml resulted in wilt within an hour.
Presence of bacteria in holding solutions, as a possible cause for decline in water uptake in leatherleaf fern fronds has not been investigated. An earlier report indicated no "disease" organisms that could account for wilt were found on stipes of wilted or non-wilted fronds (1). However, if postharvest wilt of leatherleaf fern is similar to that reported for maidenhair fern and roses, is it possible that Clorox might increase vase life? The following experiments were conducted to determine if low levels of Clorox in holding solutions might have a positive effect on postharvest water uptake and vase life of detached leatherleaf fern fronds.
Materials and Methods
Mature, dark green fronds were harvested July 1, 1991 from ground beds under 73% shade at this research center. Fronds were taken to an air-conditioned laboratory maintained at 80 + 2°F and with a light level of 100 foot-candles at frond height from fluorescent lights 12 hours per day. Stipes were cut with a single-edge razor blade to 15 cm in length below the first pinna. They were then placed into sterilized 100 ml graduated cylinders containing sterile deionized water mixed with the following concentrations of Clorox: 0, 0.05, 0.1, 0.15, 0.2, or 0.25 ml/liter. The test was a randomized block design with 10 replications per treatment for a total of sixty fronds in this experiment. Data consisted of recording water uptake and vase life for 14 days. Phytotoxicity symptoms that developed during the experiment were rated on a visual scale of 0 to 4 where 0 = none, and 4 = severe symptoms.
The second experiment tested a 60-minute clorox pulse on water uptake and vase life of leatherleaf fronds. It was hoped that use of a pulse might stop development of phytotoxicity symptoms. Fronds were harvested on July 2, 1991 with the harvest and postharvest handling conditions the same as experiment 1. This test consisted of four treatments that involved a 60-minute pulse in solutions of Clorox at 0, 2, 20, or 200 ml/liter. Fronds were then placed in sterile 100 ml graduated cylinders containing sterile deionized water and solution uptake and vase life were monitored for 12 days. The test was a randomized block design with 5 replications.
Results and Discussion
No postharvest wilt occurred in either experiment. However, adding Clorox to holding solutions resulted in significantly greater solution uptake (Table 1). Increased uptake was accompanied by phytotoxicity in all treatments with clorox that was apparent within 3-4 days. Phytotoxicity consisted of yellowing of pinnules beginning at the center and extending outward accompanied by browning of edges. Use of a 60-minute pulse also increased water uptake and resulted in lower, but still unacceptable, levels of phytotoxicity.
Use of Clorox in the holding solution or as a 60-minute pulse treatment apparently reduced plugging of stipes (Table 2). It is possible that this was due to prevention of bacterial build-up in the holding solution. Similar effects from pulsing may indicate that the bacterial origin was either on or within the stipe. Attempts should be made to isolate and culture any bacteria that may be present on stipes and test its effects on water uptake and vase life of leatherleaf fern.
Table 1. Effect of six different levels of clorox in the holding solution on cumulative water uptake and wilt and phytotoxicity symptoms of detached fronds of leatherleaf fern 14 days postharvest.
| Clorox conc (ml/liter) |
Total water uptake (ml) |
Percent Wilt |
Phytotoxicity Ratingz |
| 0.00 | 79.3 | 0 | 0.0 |
| 0.05 | 193.1 | 0 | 2.0 |
| 0.10 | 169.3 | 0 | 2.0 |
| 0.15 | 154.8 | 0 | 2.1 |
| 0.20 | 155.9 | 0 | 2.6 |
| 0.25 | 171.0 | 0 | 2.4 |
| F-test significancey |
* | ns | * |
zVisual rating where 0 = no discoloration, 1 =
slight, 2 - moderate and 3 = severe.
ySignificance where * = 0.05 and ns = nonsignificant.
Table 2. Effect of a 60-minute clorox pulse at four different concentrations on cumulative water uptake and wilt and phytotoxicity symptoms of detached leatherleaf fern fronds during 11 days postharvest.
| Treatment Clorox conc (ml/liter) |
Total water uptake (ml) |
Percent wilt |
Phytotoxicity Ratingz |
| 0.0 | 91.6 | 0 | 0.3 |
| 2.0 | 106.0 | 0 | 1.3 |
| 20.0 | 119.0 | 0 | 1.2 |
| 200.0 | 240.0 | 0 | 1.8 |
| F-Test significancey |
* | ns | * |
zVisual rating where 0 = no discoloration, 1 =
slight, 2 = moderate and 3 = severe.
ySignificance where * = 0.05 and ns = nonsignificant.
*Professor, Environmental Horticulture and Senior Biologist, Central Florida Research and Education Center - Apopka, 2807 Binion Road, Apopka, FL 32703-8504, respectively.
Literature Cited
1. Conover, C.A., R.T. Poole and L.L. Loadholtz. 1979. Update on leatherleaf fern wilt. ARC-Apopka Research Report RH-79-1.
2. Henny, R.J. and W.C. Fooshee. 1984. Daily recutting of stipe affects postharvest vase-life, water uptake and fresh weight change of leatherleaf fern fronds. AREC-Apopka Research Report RH-84-25.
3. Nell, T.A., C.A. Conover, J.E. Barrett and R.T. Poole. 1985. Effects of pre- and postharvest anti-transpirant applications on vase life of leatherleaf fern. Scientia Horticulturae 26:225-230.
4. Stamps, R.H. 1984. Production temperature effects on anatomy, morphology, physiology and postharvest longevity of leatherleaf fern (Rumohra adiantiformis Forst. Ching). PhD Dissertation, University of Florida, Gainesville. 122 pp.
5. Stamps, R.H., T.A. Nell and D.J. Cantliffe. 1989. Production temperature affects leatherleaf fern postharvest desiccation. HortScience 24(2):325-327.
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.
7. Van Doorn, W.G., H.C.E.M. Buis and Y. de Witte. 1986. Effect of exogenous bacterial concentrations on water relations of cut rose flowers II. Bacteria in the vase solution. Acta Horticulturae 181:463-465.