Can a new giant salvinia infestation occur even if most of

the mat is destroyed except for the protected buds? From

this study, we are able to conclude that buds can produce

new growth under certain stressful conditions. They must be

greater than 0.2 cm in length and they must possess greater

than 30% moisture content to survive

Dick, Gary O.

Owens, Chetta Sl

Smart, R. Michael

Aquatic Commons

 J. Aquat. Plant Manage.
 
 42: 2004. 117
 
J. Aquat. Plant Manage.
 
 42: 117-119
Regeneration of Giant Salvinia from Apical
and Axillary Buds following Desiccation
or Physical Damage
 
CHETTA S. OWENS
 
1
 
, R. MICHAEL SMART
 
2
 
, AND GARY O. DICK
 
3
 
INTRODUCTION
 
Giant salvinia (
 
Salvinia molesta
 
 Mitchell) is a floating aquat-
ic fern native to southeastern Brazil and currently found in
tropical to temperate regions around the world. This species
has been reported in more than 20 countries, usually intro-
duced as an aquarium or water garden ornamental (Room et
al. 1981). Dense mats of giant salvinia can impede water-
based transportation, irrigation, hydroelectric production,
and flood and mosquito control. These mats can also destroy
fish and wildlife habitats, degrade water quality, and hinder
endeavors such as rice cultivation and fishing (Holm et al.
1977, Mitchell 1979). An aggressive aquatic species, giant sal-
vinia can completely cover water surfaces and has been shown
to form mats up to 1 m thick (Thomas and Room 1986).
Each ramet of giant salvinia possesses a horizontal rhizome
comprised of an internode, a node, two floating leaves, a third
modified leaf that acts as a root, an apical bud and axillary
buds (Bonnet 1955, Room 1983). Due to occasional branch-
ing, several ramets may appear along a rhizome. Also, as indi-
vidual leaf pairs contain at least a pair of axillary buds
collectively, these structures can be considered a ramet as well.
Because giant salvinia does not reproduce sexually (Oliver
1993), its survival during periods of stress depends on pro-
tection of meristematic tissues in buds on the rhizome. The
rhizomes of the species fragment easily and new plants arise
from apical and axillary buds (Harley and Mitchell 1981). In
uncrowded populations, buds are generally found a few cen-
timeters underwater. However in dense mats, some buds are
exposed to air (Whiteman and Room 1991). Thick mats can
provide protection to buds even when frost or freezing air
temperatures kill the floating leaves. Sufficient portions of
the buds are protected to regenerate the population when
more favorable environmental conditions prevail (Harley
and Mitchell 1981, Whiteman and Room 1991).
Under nitrogen-rich, uncrowded conditions, vegetative
fragmentation can occur. As each bud develops, older rhi-
zomes develop abscission layers resulting in fragmentation
and widespread dispersal of protected buds (Harley and
Mitchell 1981, Jacono and Pitman 2001). Giant salvinia buds
can also be dispersed when mats of the plant are disturbed
by human activities, wave action, wind, animal movement or
flooding (Oliver 1993, Smart et al. 1999).
Because the apical buds are protected to ensure better
survival of giant salvinia, this study focused on the effects of
1) drying of buds, and 2) new growth based on bud size.
 
METHODS
 
This study was conducted at the Lewisville Aquatic Ecosys-
tem Research Facility (LAERF) in Lewisville, TX. All experi-
ments were conducted using small plastic ice-cube trays with
14 slot filled with DI (deionized) water. Trays were main-
tained at room temperature under fluorescent lights set with
a timer to provide a 14:10 light: dark photoperiod. Giant sal-
vinia was obtained from outdoor research ponds maintained
at the LAERF. Located in the USDA hardiness zone 7b, the
LAERF (latitude 33°04’45”N, longitude 96°57’30”W) is one
of the more northern locations at which the giant salvinia is
known to overwinter in the United States (Owens et al. 2004).
 
Experiment 1. Effects of Desiccation
 
Duplicate pairs of mature, erect giant salvinia leaves with a
protected apical bud were excised from ramets, and placed
onto a wire drying rack at ambient room temperature and
held different intervals of 0, 0.5, 1.0, 1.5, 2.0, 2.5, 3, 3.5, 4,
and 6 hours. At the end of each desiccation period, one of
the paired plants was weighed, dried, and reweighed to de-
termine moisture content while the other was assayed to de-
termine viability. Viability was determined by placing the
dried leaf pair into a DI water filled and numbered slot in
the tray. After 30 days, viability as determined by visible new
growth of each bud was noted and recorded. Ten replicate
buds were excised per drying time. An ANOVA was per-
formed with a Tukey’s being used to determine statistical dif-
ferences among the means.
 
Experiment 2. Effects of Bud Size
 
Fifty apical and axillary buds were excised, measured for
length (cm) and width (cm), and placed separately into the
DI water filled slots for observation of new growth for 30 days.
Five size classes of the buds were established based on 0.1 cm
increments in length, ranging from a minimum length of 0.2
cm to a maximum of 0.6 cm (Table 1). A regression was em-
ployed comparing viability (%) with moisture content (%).
 
1
 
Analytical Services, Inc., Lewisville Aquatic Ecosystem Research Facility,
201 E. Jones St., Lewisville, TX 75057.
 
2
 
USAE-Lewisville Aquatic Ecosystem Research Facility, 201 E. Jones St.,
Lewisville, TX 75057.
 
3
 
University of North Texas-Lewisville Aquatic Ecosystem Research Facil-
ity, 201 E. Jones St., Lewisville, TX 75057.
Received for publication April 30, 2004 and in revised form June 15, 2004.
 118
 
J. Aquat. Plant Manage.
 
 42: 2004.
 
Figure 1. (A) Percent moisture content for giant salvinia dried for different periods of time, and (B) Percent viability by percent moisture content for giant
salvinia.
 J. Aquat. Plant Manage.
 
 42: 2004. 119
 
RESULTS AND DISCUSSION
 
Moisture content of exposed, excised salvinia steadily de-
creased over the desiccation period (Figure 1). Significant
differences in moisture content were observed between the
undesiccated control and all treatments; however, effects on
viability were not observed until the salvinia buds had dried
for 2.5 hours. At 2 hours drying, new growth was still ob-
served for greater than 80% of the buds by the 2.5 hour dry-
ing, new growth was reduced to approximately 40% even
though moisture content was only 1% less than the giant sal-
vinia buds that were dried for 2.0 hour. No new growth was
exhibited at 4 or 6 hours drying. It appears that moisture
content of less than 30% affects viability of giant salvinia
buds (Figure 1 A, B).
Giant salvinia buds (apical and lateral) that measured 0.2
cm or less did not produce new growth during the 30-day ex-
perimental time period. Sixty-seven percent of giant salvinia
buds that measured 0.3 cm in length produced new growth
and all buds that measured 0.4 cm and greater produced
new growth in 30 days (Table 1). Most buds in fact produced
the new growth within 2 weeks after the buds were placed in-
to DI water. There were no significant differences found be-
tween apical and lateral buds. Although not measured,
perhaps nutrients and carbohydrates were not sufficient to
provide new growth in buds measuring less than 0.2 cm.
Can a new giant salvinia infestation occur even if most of
the mat is destroyed except for the protected buds? From
this study, we are able to conclude that buds can produce
new growth under certain stressful conditions. They must be
greater than 0.2 cm in length and they must possess greater
than 30% moisture content to survive. It is likely that buds
must also contain sufficient stored nutrients and carbohy-
drates to produce new growth, but analysis of these require-
ments awaits further study.
Herbicide treatments on Lake Conroe, TX for control of
giant salvinia found that even though good spray coverage
was achieved with the contact herbicide diquat, after approx-
imately 2 weeks post-treatment, juvenile giant salvinia was ob-
served, suggesting regrowth via the protected buds. Usage of
a systemic herbicide containing the active ingredient glypho-
sate enabled better control of giant salvinia on Lake Conroe
due to the internal translocation of the herbicide to the pro-
tected buds (B. Kellum, pers. comm.).
 
4
 
Additionally, Owens et al. 2004 found that protection of
the giant salvinia buds, during freeze events at the LAERF
enabled the giant salvinia to overwinter and resume growth
in the ponds as air temperatures warmed. Buds are, after all,
the vegetative means for giant salvinia to disperse through-
out invaded aquatic systems.
 
ACKNOWLEDGMENTS
 
This research was conducted under the U.S. Army Corps
of Engineers Aquatic Plant Control Research Program, U.S.
Army Engineers Research and Development Center. Permis-
sion to publish this information was granted by the Chief of
Engineers. We would like to thank Lee Ann Glomski and
Dwilette McFarland for review of the paper.
 
LITERATURE CITED
 
Harley, K. L. S. and D. S. Mitchell. 1981. The biology of Australian weeds 6.
 
Salvinia molesta 
 
D.S. Mitchell. J. Aust. Inst. of Agr. Sci. 47:67-76.
Holm, L. G., D. L. Plunknett, J. V. Pancho and J. P. Herberger. 1977. The
world’s worst weeds. Univ. Press of Hawaii, Honolulu. 609 pp.
Jacono, C. and B. Pittman. 2001. 
 
Salvinia molesta
 
: Around the world in 70
years. Aquat. Nuisance Sp. 4(2):13-16.
Mitchell, D. S. 1979. The incidence and management of 
 
Salvinia molesta
 
 in
Papua New Guinea. Draft Rep., Office Envir. Conserv. Papua, New Guinea.
Oliver, J. D. 1993. A review of the biology of giant salvinia (
 
Salvinia molesta
 
Mitchell). J. Aquat. Plant Manage. 31:227-231.
Owens, C. S., R. M. Smart and R. M. Stewart. 2004. Low temperature limits
of giant salvinia. J. Aquat. Plant Manage. 42:(In press).
Room, P. M., K. L. S. Harley, I. W. Forno and D. P. Sands. 1981. Successful
biological control of the floating weed 
 
Salvinia. 
 
Nature 294:78-80.
Room, P. M. 1983. Falling-apart as a lifestyle-the rhizome architecture and
population growth of 
 
Salvinia molesta
 
. J. Eco. 17:349-365.
Room, P. M. and J. D. Kerr. 1983. Temperatures experienced by the floating
weed 
 
Salvinia molesta
 
 Mitchell and their predictions from meteorological
data. Aquat. Bot. 16:91-103.
Smart, R. M., C. Jacono and R. M. Stewart. 1999. Biological pollution threat-
ens Texas waters. Freshwat. Angler. March/April.
Thomas, P. A. and P. M. Room. 1986. Taxonomy and control of 
 
Salvinia
molesta
 
. Nature 320:581-584.
Whiteman, J. B. and P. M. Room. 1991. Temperature lethal to 
 
Salvinia
molesta
 
 Mitchell. Aquat. Bot. 40:27-35.
T
 
ABLE
 
 1. E
 
XCISED
 
 
 
BUD
 
 
 
LENGTH
 
 
 
AND
 
 
 
WIDTH
 
 (
 
CM
 
), N (
 
NUMBER
 
 
 
OF
 
 
 
REPLICATES
 
),
 
AND
 
 
 
APICAL
 
 
 
AND
 
 
 
LATERAL
 
 
 
BUD
 
 
 
VIABILITY
 
 
 
PERCENTAGES
 
 
 
FOR
 
 
 
EXPERIMENT
 
 2.
Excised bud 
length (cm) Width (cm) N
Apical buds 
(%)
Lateral buds 
(%)
0.2 0.1 10 0 0
0.3 0.15-0.2 10 67 67
0.4 0.015-0.03 10 100 100
0.5 0.02-0.03 10 100 100
0.6 0.02-0.03 10 100 100
 
4
 
Blake Kellum, San Jacinto River Authority, P.O. Box 329, Conroe, TX.


Regeneration of Giant Salvinia from Apical and Axillary Buds following Desiccation or Physical Damage

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Regeneration of Giant Salvinia from Apical and Axillary Buds following Desiccation or Physical Damage

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