Salvinia molesta

D. S. Mitchell (Salviniaceae), variously

called giant salvinia, water fern or African payal, is a vegetatively

reproducing, perennial, free-floating, aquatic weed,

native to southeastern Brazil (Waterhouse and Norris 1987).

It (hereafter called salvinia) is a very serious weed in most

regions outside its native range (Harley and Mitchell 1981)

including India. The purpose of this paper is to report

on two fungal pathogens that were found to be the cause

of a sudden decline in salvinia in Bangalore.(PDF has 4 pages.

Kumar, P. Sreerama

Ramani, S.

Singh, S. P.

English

Aquatic Commons

 J. Aquat. Plant Manage.
 
 43: 2005. 105
 
ACKNOWLEDGMENTS
 
The authors would like to thank the Aquatic Ecosystem
Restoration Foundation and Syngenta for sponsoring this
study. We also thank Angela Poovey and Chetta Owens for
early reviews of this article. Permission was granted by the
Chief of Engineers to publish this information.
 
LITERATURE CITED
 
American Public Health Association, American Water Works Association,
and Water Pollution Control Federation. 1989. Standard methods for
the examination of water and wastewater. 17th ed., American Public
Health Association, Washington, DC.
Bowmer, K. H., S. W. L. Jacobs and G. R. Sainty. 1995. Identification, biology
and management of 
 
Elodea canadensis
 
, Hydrocharitaceae. J. Aquat. Plant
Manage. 33:13-19.
Davies, P. J. and D. E. Seaman. 1968. Uptake and translocation of diquat in
elodea. Weed Sci. 16(3):293-295.
Frank, P. A., N. Dechoretz and R. W. Raines. 1979. Combinations of diquat
and several cations for control of hydrilla (
 
Hydrilla verticillata
 
). Weed Sci.
27(1):115-118.
Hess, F. D. 2000. Light-dependent herbicides: an overview. Weed Sci. 48:160-
170.
Hiltebran, R. D. 1965. The effect of diquat on aquatic plants in central Illi-
nois. Weeds 13(1):71-72.
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tion of a new formulation of Reward Landscape and Aquatic Herbicide
for control of duckweed, waterhyacinth, waterlettuce, and hydrilla.
J. Aquat. Plant Manage. 40:51-53.
Pennington, T. G., J. G. Skogerboe and K. D. Getsinger. 2002. Herbicide/
copper combinations for improved control of 
 
Hydrilla verticillata
 
.
J. Aquat. Plant Manage. 39:56-58.
Sculthorpe, C. D. 1967. The biology of aquatic vascular plants. Edward
Arnold, London. 610 pp.
U.S. Environmental Protection Agency. 1997. Method 549.2: Determination
of diquat and paraquat in drinking water by liquid-solid extraction and
high performance liquid chromatography with ultraviolet detection.
National Exposure Research Laboratory Office of Research and Devel-
opment, Cincinnati, OH 45268.
Van, T. K., K. K. Steward and R. D. Conant. 1987. Responses of monoecious
and dioecious hydrilla (
 
Hydrilla verticillata
 
) to various concentrations
and exposures of diquat. Weed Science 35:247-252.
Weed Science Society of America. 2002. Herbicide Handbook. Eighth Edi-
tion. W. K. Vencill (ed.). Lawrence, KS. 493 pp.
Yeo, R. R. 1967. Dissipation of diquat and paraquat and effects on aquatic
weeds and fish. Weeds 15(1):42-46.
Natural Suppression of the Aquatic Weed,
 
Salvinia molesta
 
 D. S. Mitchell, by Two
Previously Unreported Fungal Pathogens
 
P. SREERAMA KUMAR, S. RAMANI AND S. P. SINGH
 
INTRODUCTION
 
Salvinia molesta
 
 D. S. Mitchell (Salviniaceae), variously
called giant salvinia, water fern or African payal, is a vegeta-
tively reproducing, perennial, free-floating, aquatic weed,
native to southeastern Brazil (Waterhouse and Norris 1987).
It (hereafter called salvinia) is a very serious weed in most
regions outside its native range (Harley and Mitchell 1981)
including India. Although there are different views on the en-
try and introduction of salvinia into India, it was first observed
in the 1950s in Veli Lake, Trivandrum (now Thiruvanan-
thapuram, Kerala), and in 1964 it assumed pest status (Joy
1978). It has both direct and indirect effects on the aquatic
environment, especially due to its habit of choking rivers, ca-
nals, lagoons and other water bodies. The most-affected crop
plant is rice, where salvinia infestations can interfere with cul-
tivation and reduce yields by competing for available nutri-
ents (Singh 1989). As a classical biological control measure,
two insect species were introduced into India to suppress sal-
vinia. Although the performance of the grasshopper, 
 
Paulinia
acuminata
 
 De Geer, imported from Trinidad in 1974, was not
satisfactory (Joy et al. 1981), 
 
Cyrtobagous salviniae
 
 Calder &
Sands of Brazilian origin introduced in 1982 from insect pop-
ulations in Australia has been successful (Jayanth 1987). Not-
withstanding this, the need for additional agents is highly
desirable because salvinia remains problematic in India. In-
tensive surveys were conducted in different parts of the coun-
try to identify pathogens with potential to act as biological
control agents of the weed. The purpose of this paper is to re-
port on two fungal pathogens that were found to be the cause
of a sudden decline in salvinia in Bangalore.
 
MATERIALS AND METHODS
 
In the process of maintaining 
 
C. salviniae
 
 colonies at the
Project Directorate of Biological Control, Bangalore, healthy
salvinia plants were brought from water bodies in and around
 
Project Directorate of Biological Control, P. B. No. 2491, H. A. Farm
Post, Hebbal, Bellary Road, Bangalore 560 024, Karnataka, India; e-mail:
psreeramakumar@gmail.com. Received for publication March 2, 2005 and
in revised form July 15, 2005
 
J. Aquat. Plant Manage.
 
 43: 105-107
 106
 
J. Aquat. Plant Manage.
 
 43: 2005.
Thrissur, Kerala, and from the Indian Institute of Horticul-
tural Research, Bangalore in August 1998. During June 1999,
the cultures (most of them ‘tertiary forms’) were suppressed
due to extensive fungal growth. This ultimately brought
about a total decline of the mats in all the culture tanks.
A close observation of the affected plants revealed the
presence of extensive fungal hyphae along leaf margins as
well as on the laminae. Plant samples were collected on 11
June 1999 for isolating and studying the associated organ-
ism(s). Plating of surface-sterilized, excised diseased leaf tis-
sues on tap-water agar (agar, 18 g; streptomycin sulphate, 0.2
g; tap water, 1 L) yielded two different fungi when incubated
at 25°C in an incubator set to a 12-h photoperiod. Single-
conidial isolates of the two species were propagated on Cza-
pek-Dox agar (HiMedia, Mumbai, India) to study morpho-
logical and growth characteristics in culture for preliminary
identification of the species.
The two fungal species were assayed separately for patho-
genicity. Mycelial and conidial suspensions of each pathogen
were prepared by adding 20% w/v or 1 
 
×
 
 10
 
6
 
 and 1 
 
×
 
 10
 
7
 
conidia/ml, respectively to sterile distilled water containing
0.05% Tween 20. Mycelia of each species were grown sepa-
rately in 250-ml Erlenmeyer flasks each containing 100 ml of
potato dextrose broth (HiMedia) for 5 days on a rotary shak-
er at 200 rpm under room conditions (28 ± 2°C). The sub-
merged mycelium thus obtained was filtered through four
layers of cheesecloth and blended in a mixer for 30 seconds
and used for preparing the mycelial suspension. Conidia were
obtained from sporulating cultures grown on homemade po-
tato dextrose agar in 90-mm petri plates by flooding them
with sterile distilled water. Final conidial counts were assessed
with a haemocytometer. Salvinia plants used in the experi-
ments were ‘secondary forms’ that were grown under partial
shade conditions in 17-cm diameter (inner brim) plastic pots
containing tap water up to 5 cm from the brim. The test
plants were removed from the water and spread over a sheet
of filter paper before spraying the inoculum from a close dis-
tance till run off. Sprayed plants were put back into the re-
spective pots for incubation and further observations. Plants
sprayed with only sterile water containing the surfactant
served as controls. Each treatment was replicated 10 times.
Fifteen days post inoculation, 30 pairs of opposite leaves per
pot were randomly assessed for percent disease incidence. A
pair of floating leaves was considered to be diseased only
when both leaves were totally covered with lesions as original-
ly observed under natural conditions. Observations were con-
tinued further for another 15 days. Pots were replenished
with tap water as needed to maintain the original level.
 
RESULTS AND DISCUSSION
 
Mycelial suspensions of both the fungi were ineffective in
causing disease in salvinia (Table 1). In all likelihood the
mycelium dried on the plant surfaces and rendered it inac-
tive before it could invade the host tissues. The two conidial
concentrations were infective and induced disease. The two
fungi induced at first water-soaked lesions, which later ex-
panded to form larger patches. As disease progressed myce-
lial growth was evident along the leaf margins leading to
drying of leaf tissues. By 30 days post inoculation, severely
infected plants started to disintegrate and collapse into the
water. Both fungi could be reisolated and were able to subse-
quently induce disease upon fresh inoculation to healthy sal-
vinia plants, thus satisfying Koch’s postulates. However, the
disease induced artificially was not as severe as that observed
in the culture tanks in 1999. It is conjectured that lower con-
centrations of inoculum combined with incubation condi-
tions were less than optimum for disease development.
The two isolates designated as WF(Sm)37 and WF(Sm)38
were identified as 
 
Phoma glomerata
 
 (Cda) Wollenw. &
Hochapf. and 
 
Nigrospora sphaerica
 
 (Sacc.) Mason, respective-
ly. The same fungal species were isolated in subsequent years,
though their impact on the weed was not as damaging as in
1999. There is no previous record of these two fungi as
pathogens of salvinia anywhere in the world. Prior to the
present work, the association of only two fungi, 
 
Myrothecium
roridum
 
 Tode ex Fries with decaying mats in Kakki Reservoir,
Sabarigiri, Kerala and 
 
Verticillium nigrescens
 
 Pethybridge with
living salvinia leaves in Bangalore (Ponnappa 1977) was
known in India. Recently, 
 
Rhizoctonia solani
 
 Kühn has been
implicated as a pathogen of both 
 
S. molesta
 
 and 
 
S. minima
 
Baker in Florida, USA (Rayachhetry et al. 2002).
The pathogens reported herein merit further consider-
ation and evaluation, in spite of their ubiquitousness. Howev-
er, commercialization of 
 
P. glomerata
 
 or 
 
N. sphaerica
 
 as
mycoherbicides for salvinia will require additional research
on host-specificity, strain variations, efficacy, mass production
and formulation.
 
T
 
ABLE
 
 1. E
 
VALUATION
 
 
 
OF
 
 
 
TWO
 
 
 
NEWLY
 
 
 
IDENTIFIED
 
 
 
PATHOGENS
 
 
 
AGAINST
 
 
 
S
 
ALVINIA
 
 
 
MOLESTA
 
.
 
Inoculum
Percent disease incidence
 
Phoma glomerata Nigrospora sphaerica
 
Mycelial suspension (20% w/v) 3.3 (7.2)
 
a
 
3.0 (7.6)
Conidial suspension (1 
 
×
 
 10
 
6
 
 conidia/ml) 29.3 (32.8) 25.0 (29.9)
Conidial suspension (1 
 
×
 
 10
 
7 
 
conidia/ml) 62.0 (52.1) 53.3 (47.0)
SEM
 
b
 
 (±) 2.1 2.0
CD
 
c
 
 (
 
P
 
 = 0.05) 6.2 5.8
 
a
 
Data in parentheses are arcsine-transformed values.
 
b
 
Standard error of mean.
 
c
 
Critical difference.
 J. Aquat. Plant Manage.
 
 43: 2005. 107
 
ACKNOWLEDGMENTS
 
The financial help provided by the Department of Bio-
technology, Government of India, in the form of a project
for establishing a National Repository of Natural Enemies of
Crop Pests and Weeds is gratefully acknowledged. Thanks
are due to Dr. Alaka Pande, Agharkar Research Institute,
Pune, for the identification of the two fungal species.
 
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. Agric. Sci. 47:67-76.
Jayanth, K. P. 1987. Biological control of the water fern 
 
Salvinia molesta
 
infesting a lily pond in Bangalore (India) by 
 
Cyrtobagous
 
 
 
salviniae
 
. Ento-
mophaga 32: 163-165.
Joy, P. J. 1978. Ecology and Control of 
 
Salvinia
 
 (African Payal) the Molesting
Weed of Kerala. Technical Bulletin No. 2, Kerala Agricultural University,
Trichur, India. 40 pp.
Joy, P. J., K. C. Varghese and C. C. Abraham. 1981. Studies on biology and
host range of 
 
Paulinia acuminata
 
 De Geer (Orthoptera: Acrididae) and
its efficacy for the control of 
 
Salvinia molesta
 
 Mitchell—an aquatic float-
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In
 
: B. V. V. Rao (ed.). Proceedings of the
Eighth Asian-Pacific Weed Science Society Conference, 22-29 November
1981, Bangalore, India.
Ponnappa, K. M. 1977. Records of plant pathogens associated with eight
aquatic weeds in India. Technical Bulletin No. 18 of the Commonwealth
Institute of Biological Control, Commonwealth Agricultural Bureaux,
Slough, England. pp. 65-74.
Rayachhetry, M. B., T. R. Center, T. D. Center, P. Tipping, P. D. Pratt and
T. K. Van. 2002. First report of the pathogenicity of 
 
Rhizoctonia solani 
 
on
 
Salvinia molesta 
 
and 
 
S. minima 
 
in Florida. Plant Dis. 86: 813.
Singh, S. P. 1989. Biological Suppression of Weeds. Technical Bulletin No. 1,
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Waterhouse, D. F. and K. R. Norris. 1987. Biological Control: Pacific Pros-
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Natural Suppression of the Aquatic Weed Salvinia molesta D.S. Mitchell, by Two Previously Unreported Fungal Pathogens

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Natural Suppression of the Aquatic Weed Salvinia molesta D.S. Mitchell, by Two Previously Unreported Fungal Pathogens

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