S -r, A Summary of Research Concerning Postharvest Wilt
of Detached Leatherleaf Fern Fronds
R.J. Henny, R.H. Stamps and W.C. Fooshee1
University of Florida, IFAS SP 3 0 1994
Central Florida Research and Education Center Apopka
CFREC-Apopka Research Report RH-92-2 University of Florida
Postharvest wilt of leatherleaf fern fronds is a continuing problem for commercial
producers in Florida. Two types of postharvest decline of leatherleaf fern fronds are
discussed in the literature: 1) wilt; and 2) yellowing. Fern wilt is characterized by partial or
complete folding of green pinna (leaflets) along the midvein and/or loss of overall rigidity of
the frond while yellowing of fronds begins along the midveins of pinna and spreads toward
the margins (11).
Fern wilt has also been called frond 'curl' (7) to distinguish it from various types of
wilt diseases; however, in this paper 'wilt' will be used exclusively since it is the term
commonly used in industry to define premature postharvest desiccation of fronds. Yellowing
has been attributed to natural frond senescence and is considered a separate phenomenon
from wilt (5).
Both field and laboratory studies have been employed in the study of fern wilt.
Production conditions studied include type of growing structure (shadehouses or natural oak
hammocks), shade and fertilization levels, watering rates and intervals, effects of herbicides,
frond age, harvest time and conditions, season of harvest, handling procedure before and
during packing and conditions during storage and shipment. Laboratory studies have
involved gathering of data in climate controlled rooms including measurements of water
usage, fresh weight change, and vase life of individual fronds. These studies have tested
various types of floral preservatives, holding solutions, and chemical pulses and their effects
on water use and vase life.
Experiments on fern wilt usually encounter a relatively high degree of variability
within treatments. Vase life of fronds harvested from the same growing areas within a few
days of each other may be different, whereas water uptake and vase life of individual fronds
of the same weight, size, appearance and placed in the same holding solutions can be very
dissimilar. To date, there is no single explanation for these inconsistencies. This paper will
focus on published results from studies involving postharvest vase life of leatherleaf fern and
point out areas where data are consistent and what implications these data provide.
'Professor, Plant Geneticist; Associate Professor, Cut Foliage Specialist; Senior Biological
Scientist, Central Florida Research and Education Center, 2807 Binion Road, Apopka, FL
because of many interacting factors. Still there have been consistent trends in many of the
reports. In one study, fronds harvested from shadehouses had a higher incidence of wilt th
those from an oak hammock (5,4). The amount of fern wilt has also been reported to vary
between producers. Marousky (4) found that 50% of fern from one commercial source
wilted while fronds from another grower had no wilt. In a 3 year study of 3 commercial
ferneries, the overall incidence of wilt 12 days postharvest varied from 23% for one growe
to 8% for another a three-fold difference (5). In another study, the effects of light levels
varied depending on the location. There was no difference in wilt of fern harvested from
63% or 73% shade from one commercial fernery, but fern produced under 63% shade fron
a different fernery exhibited almost twice as much wilt as fern produced under the 73%
shade level (11). Finally, fern harvested from 63% or 73% shade provided by black
polypropylene fabric showed no difference in vase life (11).
Little is known about the effects of production fertilization practices on vase life.
Conover et al. (1) suggested that growers avoid urea as a source of nitrogen in favor of a
source that provides 40-60% of nitrogen in the nitrate form. In the same report, a
comparison of fern receiving 900 lbs N/A/yr versus 450 lbs N/A/yr seemed to indicate thai
fertilization level was not a factor. In another experiment, fronds produced using 750 lbs
N/A/yr and 1500 Ibs/N/A/yr had the same vase life (15).
Fern wilt has been shown to be seasonal with the highest occurrences during hot
periods. Mathur et al. (5) found that most wilt occurred from July through October. In a
similar study (9), it was found that fronds developed from fiddleheads emerging in June, Ji
and August had the shortest vase life. These findings were verified by a third study (11) ir
which it was suggested that high temperature stress during these months may contribute to
wilt. Similar declines in frond vase life for fronds produced during hot weather compared
those produced during cooler weather have been reported (15). Effects of production
temperature on vase life have also been studied using growth chambers. One study involve
high (86*F day/770F night) and low (68*F day/59F night) temperature regimes both with
the same light levels; vase life of fronds grown at the high temperature regime was 28 to
66% less than those grown at the low temperature regime (13). This data supports the
observation of shorter vase life for fronds harvested during the summer months. Stamps (2
conducted another similar study using growth chambers and found that 81% of fronds
produced at the high (95/75*F) temperature regime exhibited desiccation symptoms while
none of those from the low (75/550F) temperature regime did.
Other environmental factors need to be considered during wilt season; these include
increases in photoperiod and total irradiation, high night temperatures and amount of water
the fern beds receive (either rainfall or irrigation). Of those four factors, only irrigation
levels have been mentioned in the literature. Conover et al. (1) mentioned that overwaterin
nf fpmrn wan a ftrtnr that ceP.mpn tn navravatPe wilt This wnmld rnrr.~nnnnd with the. hiphewr
rain levels occurring during the summer months. A reduction of irrigation level by
approximately 50% resulted in increased vase life on 3 of 7 dates in one study (6). In
another study, fern from beds that had been watered the day before harvest did not last as
long as fern from beds that had not been watered for a week (10).
Pesticides are used routinely during the production of leatherleaf fern, especially
during the summer months when fern wilt is most prevalent. Several studies have been
conducted to determine if pesticides affect fern vase life. The first study (22) examined
possible effects of selective herbicides on vase life. None of the herbicide treatments
reduced vase life compared to the untreated control. In fact, vase life of oxadiazon treated
fronds was greater than the control for one harvest. A subsequent study of four herbicides
applied in 15 rates and combinations, again, found no herbicide effect on vase life (22). A
short term study of the effects of two fungicides benomyll and mancozeb) commonly used on
leatherleaf fern showed no effect on vase life (17).
Frond age at the time of harvest has been shown to be a significant factor in vase life.
Marousky (4) showed that fronds with mature pinnae had a greater degree of wilt than fronds
with immature pinnae. In that study, mature fronds were dark green, fully expanded and
commercially acceptable while an experienced fern cutter judged immature fronds to be 2.5
weeks younger than mature fronds. Another extensive study involved tagging newly
emerged fiddleheads every 4 weeks for 1 year. Fronds were harvested 6 weeks after tagging
and again at 4-week intervals until 6 harvests had been completed. Fronds harvested 6
weeks after emergence usually had longer vase life than older fern although results were
Since harvested fronds are commonly dipped in various solutions before being packed
and stored, these factors have been investigated to test for effects on vase life (14). Data
indicate that leatherleaf fern fronds are tolerant of storage. Two studies found that storage of
fronds did not affect vase life (16, 19); however, a storage temperature of 40F for 10, 21 or
31 days was reported to be better than 75F (16). It was also found that prestorage dipping
of fronds in the fungicides benomyl or iprodione was not detrimental to subsequent vase life
:rmanent wilting point). These rehydrated fronds showed an average gain of 31.8% in
esh weight during this period. In addition to implicating water deficits, such data indicate
at factors in the lower 1 centimeter of the stipe are significantly involved in the occurrence
Swilt. Characterizing the nature of these factors and their effect on frond water relations is
key step in understanding wilt.
The water uptake curve of individual fronds is another consistent postharvest response
'leatherleaf fern fronds. Water uptake during the first 24 hour period exceeds that taken
During the second 24 hour period. The rate of subsequent water uptake continues to
cline over the course of 5-7 days and then remains fairly constant, though at a much lower
te than during the first day. There may be differences in total water uptake between
periments, but the slope of the uptake curves remains similar. This decline in water
take has been shown to be logarithmic/exponential (13, 21).
Possible explanations for the observed decline in water uptake include: the gradual
)sing of stomates retarding the amount of water loss by the frond; development of blockage
the vascular system reducing the ability of the stipe to transport water; or, a combination
stomatal closure and stipe blockage.
If stomatal closure is a significant factor in reducing water uptake, they apparently
)se gradually over several days or water uptake would be less than observed during the
'st 24 hour period; however, this would conflict with reports that stomates close within a
w hours after cutting (7). In that study, frond water potentials, as measured by a diffusive
distance porometer, indicated that stomata began to close within 30 minutes of harvest.
tempts to check for stomatal closure by microscopic examination have not been conclusive
cause of difficulty in determining if stomates are open or closed by visual examination
me (Henny and Fooshee, unpublished). Stomatal impressions taken from fronds at
'ferent times or conditions appear similar.
The occurrence of some type of vascular blockage has been suggested in the literature
7, 3). Unfortunately, evidence is still indirect and based on water uptake data. The only
empt to locate blockage using a scanning electron microscope did not show any vascular
xckage (7); however, it is possible that the blockage was lost during specimen preparation.
is interesting to note that frond:, grown at higher temperatures in growth chamber studies
d narrower stipes with fewer vascular bundles and smaller tracheid lumen areas compared
fronds grown at lower temperatures (13). Fronds with reduced vascular systems took up
s water, lost weight more rapidly and had reduced vase life compared to fronds with
ger stipes. Since frond surface areas and stomatal densities were not different, the
luced water uptake was probably due to the restricted vascular system. In fact, stipe water
iductivities measured at the time the fronds were placed in water were lower for the
Water uptake data strongly indicate that some form of vascular blockage is located in
basal 1 cm of the stipe. Total water uptake in detached fronds increased when 1 cm was
L;uve rtaUIieU a similar siupe as unIuL IUllnus ki.e. uecreasmg over ume), out me ltota
amount of water uptake approximately doubled that of fronds that were not recut. Possible
explanations for these results are that either stomates close gradually over several days
following harvest reducing water loss and hence a need for uptake, or blockage, initially
present only in the base of the stipe, progresses throughout the entire stipe. One argument
against progressive blockage is that rehydration of fronds, that did not wilt until several days
after harvest, can be achieved by recutting the basal 1 cm of the stipe. Had blockage
progressed throughout the stipe during this time, recutting only the base would have little
Discussion of stomates, vascular blockage and water uptake leads to an apparent
contradiction: chemically extended vase life of fronds has not been correlated with higher
amounts of water uptake (Stamps, 1983). In fact, postharvest treatments involving holding
solutions or pulses that increase solution uptake were inversely related to vase life. This is
based on data from tests using holding solutions consisting of low pH, 200 ppm 8-
hydroxyquinoline citrate or 200 ppm citric acid (19). In each case, solution uptake was
greater than for fronds held in deionized water, but vase life was reduced. Similarly, fronds
that were put under water stress following harvest took up more water, but had shorter vase
life than nonstressed fronds that took up less water (7). Stamps and Johnson (18) also
reported a negative correlation between vase life and water uptake. The only exception is the
case of daily recutting of fronds; this treatment increases both daily water uptake and vase
life (3). It should be noted that recutting involves only the basal one centimeter of the frond
and not the physiology of the entire frond as do chemical treatments.
An alternative approach to increasing water uptake to maintain water balance in
harvested fern fronds has been the use of antitranspirants to reduce water loss (8).
Antitranspirants were applied as field sprays 3-28 days before harvest or as postharvest dips.
Field application did not affect postharvest water use whereas postharvest dips reduced water
jse during the first 24 hours; however, the incidence of wilt was not affected by either
treatmentt method. In addition, sticky residues from pinolene-based antitranspirants were a
problem on treated fronds.
Stamps and Nell (20) showed that pulses containing ethylene inhibitors did not extend
vase life, indicating that sensitivity to ethylene was probably not a factor in wilt. Pulsing for
10-15 minutes with 800 or 1000 ppm 8-hydroxyquinoline citrate increased vase life compared
:o water controls in two different reports (19, 20).
An intriguing aspect of fern wilt is that 2 fronds can be similar in appearance and
size, harvested from the same bed, with similar postharvest water-uptake curves and yet one
will wilt within a few days while the other may last for weeks. Such results may point to
physiological conditions predisposing fern to wilting under certain conditions. This concept
ias been mentioned in the literature (7) and determining the nature of this condition may be
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Research Report RH-82-23.
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life, water uptake and fresh weight change of leatherleaf fern fronds. AREC-Apopka
Research Report RH-84-25.
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maturities from various growing environments. Proc. Fla. State Hort. Soc. 96:270-
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of leatherleaf fern. Proc. Fla. State Hort. Soc. 95:142-143.
Mathur, D.D., R.H. Stamps and C.A. Conover. 1983. Response of Rumohra
adiantiformis to water application level and nitrogen form. HortScience 18(5):759-
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leatherleaf fern. J. Amer. Soc. Hort. Sci. 108(4):516-519.
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harvest anti-transpirant applications on vase life of leatherleaf fern. Scientia
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harvested at various times of the year and at various frond ages. Proc. Fla. State
Hort. Soc. 97:266-269.
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for the culprit. Univ. of Fla. Commercial Fern Grower 8(7):1-2.
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leatherleaf fern. ARC-Apopka Research Report RH-81-16.
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physiology and postharvest longevity of leatherleaf fern (Rumohra adiantiformis Fo
Ching). PhD Dissertation, University of Florida, Gainesville. 122 pp.
14. Stamps, R.H. 1987. Harvest time and postharvest immersion affect water uptake ani
postharvest decline of leatherleaf fern. Proc. Intern. Soc. Trop. Hort. 31:42-50.
15. Stamps, R.H. 1989. Biostimulant and high fertilizer rates do not affect leatherleaf fi
frond development, yield or vase life. Proc. Fla. State Hort. Soc. 102:274-276.
16. Stamps, R.H. and A.R. Chase. 1984. Fungal inoculation, fungicide treatments, and
storage affect postharvest decay and vase-life of leatherleaf fern fronds. HortScien,
17. Stamps, R.H. and A.R. Chase. 1987. Foliar applications of benomyl and mancozeb
not affect leatherleaf fern carbon assimilation, transpiration, light compensation poi
or vase life. Proc. Fla. State Hort. Soc. 100:362-364.
18. Stamps. R.H. and C.R. Johnson. 1984. Vesicular-arbuscular mycorrhizal inoculatio,
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.
19. 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 fe
fronds. Proc. Fla. State Hort. Soc. 96:304-306.
20. Stamps, R.H. and T.A. Nell. 1986. Pre- and postharvest treatment of cut leatherlea
fern fronds with floral preservatives. Proc. Fla. State Hort. Soc. 99:260-263.
21. Stamps, R.H., T.A. Nell and D.J. Cantliffe. 1989. Production temperature affects
leatherleaf fern postharvest desiccation. HortScience 24(2):325-327.
22. Stamps, R.H. and R.T. Poole. 1987. Herbicide effects during leatherleaf fern bed
establishment. HortScience 22:261-264.