Septoria Leaf Spot of Lantana from Ecuador: A Potential Biological Control for Bush Lantana in Forests of Hawaii

Abstract

Pathogenicity tests with a Septoria sp. isolated from Lantana camara from Ecuador showed aggressiveness to four L camara selections from Hawaii forests. The initial symptoms of the disease on inoculated leaves were chlorotic spots that appear within 2 weeks, becoming distinctly angular necrotic lesions in 4 weeks, inducing leaf chlorosis and defoliation 6 weeks after inoculation. Inoculum applied at 1 x 10 6 conidia per ml in 2% sucrose-0.5% gelatin solution produced an average of 87 lesions per leaf. Ornamental hybrids of L. camara x L. montevidensis also were susceptible, but these plants had significantly fewer lesions. All selections of L. montevidensis tested were immune. This Septoria sp. from Ecuador is the first pathogen found to be virulent on bush lantana, the most serious ecological threat to Kauai's forest, and its release is presumed to be an effective biocontrol agent for this weed.

Full text

Septoria Leaf
Spot,
a
Potential Biological Control
for
Banana Poka Vine
in
Forests
of
Hawaii
EDUARDO
E.
TRUJILLO,
Professor,
and
DAVID
J.
NORMAN, Assistant Researcher, Department
of
Plant
Pathology, University
of
Hawaii,
3190
Maile
Way, Honolulu 96822;
and
ELOISE
M.
KILLGORE,
Plant
Pathologist,
Plant Pathology Quarantine Facility, Biological Control Section, Hawaii Department
of
Agriculture, Honolulu
96814
ABSTRACT
Trujillo,
E.
E.,
Norman,
D.
J.,
and
Killgore,
E. M.
1994, Septoria leaf
spot,
a
potential biological
control
for
banana
poka
vine
in
forests
of
Hawaii.
Plant
Dis. 78:883-885.
Pathogenicity studies
in
Hawaii have confirmed
Septoria
passiflorae
as
an
aggressive pathogen
of
banana poka
(Passiflora
tripartita
var.
tripartite).
Initial symptoms
on
inoculated leaves
are
chlorotic
spots
that appear
14
days
after inoculation
and
become distinct circular lesions
with
yellow
halos
by 20
days.
The
spots develop necrotic centers
3 mm in
diameter
20-24
days
after inoculation,
and
diseased leaves turn bright yellow
and
dehisce.
Host
range
studies
confirmed
P.
foetida,
also
a
weed,
as a
susceptible host.
The
economic crops purple
and
yellow
lilikoi
and
other species tested were immune. Since
the
Passifloraceae
are not
native
to the
Hawaiian islands,
S.
passiflorae
is
presumed
to be an
environmentally safe biocontrol agent
for
these weeds
in
Hawaii.
Passiflora
tripartita (Juss.) Poir var.
tripartita
Holm-Nie.
Jorg.
&
Laws.
(=
Passiflora
mollissima
Neal),
commonly
referred
to as
"banana
poka,"
was
first
introduced into Hawaii
in
1921
as an
ornamental (5). This perennial woody
vine
with attractive pink, pendulous
flowers
and
oblong bright yellow
fruit
is
native
to the
southern Colombia
and
northern Ecuador Andean region
of
South America (12).
The
ripe, bright
yellow
fruit
resembles
a
ripe banana, thus
its
Hawaiian name.
In
Hawaii
it has
become established
at mid to
high
elevations,
800
2,200
m, on the
islands
of
Hawaii, Kauai,
and
Maui. Banana
poka
is the
most aggressive introduced
weed
of
high-elevation forest areas
in
Hawaii.
In
1981
it was
estimated
to
cover
more than
500
km2
of
forests
on
Kauai
and
Hawaii (14). Banana poka
was
classified
as a
noxious weed
in
1979
by
the
Hawaii Department
of
Agriculture
(10).
In
1981
the
State
of
Hawaii Depart-
ment
of
Land
and
Natural Resources,
Journal
Series
No.
3945,
Hawaii
Institute
of
Tropical
Agriculture
and
Human
Resources.
Accepted
for
publication
24 May
1994.
©
1994
The
American
Phytopathological
Society
Division
of
Forestry
and
Wildlife,
funded
the
exploratory search
of
South
America
for
potential biological control
agents
for
this weed. Exploration
of
Colombia
and
Ecuador Andean regions,
conducted during 1983-1984, revealed
a
number
of
insect pests
and
fungal patho-
gens
of
Passiflora
spp. with biological
control potential (7,12).
The
moth
Cyanotricha necyria Felder,
an
aggres-
sive
phytophagous pest
of
banana poka
(2),
was
introduced
in
1985
and
released
in
1989 (6),
but a
breeding population
has
failed
to
become established
so
far.
Another moth,
Pyrausta
perelegans
Hampton, introduced
m
1986
and
released
in
1989,
has
become established
but has had
negligible biological pressure
on
banana
poka.
A
powdery mildew
caused
by a
Phyllactinia
sp. and
studied
by
the
first
author
at
Providencia,
Narino, Colombia, during
1987-1989
was
approved
for
introduction
and
release
by the
Hawaii Board
of
Agricul-
ture
in
1989. However, failure
to
main-
tain viability
of
this pathogen during
transportation
has
precluded
its
success-
ful
establishment
in
Hawaii.
Hawaii banana poka seedlings planted
in
Aldana, Narino,
Colombia,
in
1991
developed
a
leaf spot disease caused
by
a
Septoria
sp.
Symptoms
of the
disease
were distinct circular lesions with
necrotic centers surrounded
by
yellow
halos.
On 19
April 1993, diseased, air-
dried
leaves were shipped
to
Hawaii
under USDA Permit
No.
930095
for
isolation, pathogenicity,
and
host range
studies.
MATERIALS
AND
METHODS
Isolation
and
pathogenicity tests.
All
research
was
performed under strict
quarantine requirements
at the
Hawaii
Department
of
Agriculture Plant Pathol-
ogy
Quarantine Facility
in
Honolulu.
Septoria
sp. was
isolated
from
lesions
with
necrotic centers
on
diseased banana
poka leaves incubated
in
moist chambers
under
fluorescent illumination
for 2
days
at 25 C.
Spore cirrhi produced
by
pycnidia
were removed aseptically
and
streaked with acidified sterile water onto
Difco
potato-dextrose agar (PDA)
plates.
After
4 days of incubation at 21
C
under continuous
fluorescent
illumi-
nation, bacteria-free cultures were
transferred
to new
plates
and
grown
for
2
wk.
Spore suspensions were made
by
flooding
14-day-old
PDA
cultures with
10
ml of
sterile distilled water
and/or
a
solution
of 2%
sucrose
and
0.5% gelatin
(11).
Spore suspensions
for
inoculations
were
adjusted
to
approximately
1 X
106
spores
per
milHliter
using hemacytometer
counts.
All
plants were kept
in a
quaran-
tined, negative
pressure,
sunlit
(40,000-
100,000
lux), air-conditioned greenhouse
maintained
at
24-25
C.
Plants
were
grown
in
15-cm-diameter
pots
filled
with
equal parts
of
soil
and
Fisons's
Sunshine
Mix
3
(Fison Horticulture Inc., Van-
couver,
BC,
Canada)
and
fertilized with
Osmocote 14-14-14. Two-month-old
banana poka seedlings were inoculated
by
spraying leaves with inoculum
to
wet-
ness.
Control plants were sprayed
with
water
or the
sugar-gelatin
solution.
Sets
of
four inoculated
and
four noninocu-
lated
plants were incubated
for 48 hr at
approximately 100% relative humidity
and 25 C in
terraria
50 cm in
diameter
and
with
an
adjustable
top
opening
to
control humidity (Lawnware Products,
Inc., Mortin Grove,
IL).
Forty-eight
Plant
Disease/September
1994
883

hours after incubation, plants were trans-
ferred
to the
quarantined greenhouse
until symptoms developed. Three weeks
after
inoculation,
the
number
of
lesions
present
on the
oldest leaf
of
each plant
was
counted,
A
one-way analysis
of
variance followed
by an LSD
test
was
used
to
compare mean lesion number
between treatments.
The
pathogenicity
test
was
repeated.
Host range studies. Two-month-old
rooted cuttings
of
banana
poka
and six
of
the
most common naturalized
Passiflora
spp.
found
in
Hawaii were
used
in
host range determinations. These
were
P.
edulis
Sims (purple
lilikoi),
P.
e.
flavicarpa
Degener (yellow lilikoi),
P.
foetida
L.
(love-in-a-mist),
P.
laurifolia
L.
(yellow granadilla),
P.
ligularis
A.L.
Juss. (sweet granadilla),
and P.
suberosa
L.
(huehue
haole).
Sets
of
four plants
of
each Passiflora spp. were inoculated
as
previously described with
1 X
106
conidia
per
milliliter. Tests were
repeated.
RESULTS
Isolation
and
pathogenicity tests.
The
Septoria
sp.
isolated from diseased
banana
poka leaves from Aldana,
Narino,
Colombia,
was
identical
in
morphology
to
Septoriapassiflorae
Syd., with conidia
35-52
X
1.5-2
/Ltm
(Fig.
1 A) and
immersed,
dark brown
to
black, globosed pycnidia
72-104
/x
in
diameter
(Fig.
ID).
This
fungus
was
originally described
in
1937
on
P.
mollissima
(Kunth)
L.H.
Bailey
from
Pichincha, Ecuador (9,13),
The
fungus
grows readily
on PDA and
produces abundant pycnidia
and
conidia
after
14
days
of
incubation
at 20 C
under
continuous fluorescent illumination.
All
banana poka plants inoculated
with
spores
in
water
or
sugar-gelatin
solution developed symptoms, whereas
noninoculated control plants were
free
of
disease.
The
number
of
lesions
per
leaf
ranged from
one to 39 on
plants inocu-
lated with
the
spore-water suspension
and
from
56 to 105 on
those inoculated
with
the
sugar-gelatin solution,
an
approximately sixfold increase
in the
number
of
spots
(Fig.
2).
Treatments
were
significantly
different
(P
<
0.05).
Symptoms were small, chlorotic leaf
spots appearing
14
days after inocula-
tion. Spots enlarged into distinct circular
lesions
with yellow halos
4-6
days later
(Fig.
IB);
the
centers were necrotic
4 wk
after
inoculation. When
the
necrotic
centers
of
lesions were approximately
3
mm in
diameter,
affected
leaves turned
bright
yellow
and
dehisced
(Fig. 1C).
Numerous cirrhi were observed protrud-
ing
from
pycnidia
on
senescent diseased
leaves
after
48 hr of
incubation
in
moist
chambers
at 25 C
(Fig.
ID).
The
patho-
gen was
reisolated
in
pure culture
from
all
inoculated banana poka plants, con-
firming
pathogenicity.
Host range studies. Besides banana
poka,
P,
foetida
was the
only other mem-
ber of the
Passifloraceae
tested that
was
susceptible
to
this isolate
of S.
passiflorae
from
Colombia (Table
1).
Purple
and
yellow
lilikoi
and
yellow
and
sweet
granadilla were
not
hosts
of S.
passiflorae.
All
banana poka plants used
as
controls developed leaf spots
3-4 wk
after
inoculation. These results were
consistently
reproduced
in
repeated tests.
E=
o
'<£
60
Fig.
1.
Septoria
leaf
spot
of
banana
poka:
(A)
Filiform,
multiseptate
spores
of
Septoria
passiflorae.
Scale
bar
=
8.46
jum.
(B)
Typical
spots
with
halos
on
banana
poka
leaf
20
days
after
inoculation.
(C)
Acute
chlorosis
before leaf
dehiscence
on
banana
poka
seedlings
24
days
after
inoculation,
(D)
Pycnidia
formation
on the
surface
of a
senescent
leaf lesion
2
days
after
incubation
in
a
moist
chamber
at 25 C.
Scale
bar =
150
fim.
Water
Sugar/gelatin
Fig.
2.
Comparison
of
mean
number
of
lesions
produced
on
leaves
of
Passiflora
tripartita
var.
tripartita
by
Septoria
passiflorae
applied
in
sterile distilled water
or 2%
sucrose
and
0.5%
gelatin
solution.
884
Plant
Disease/Vol.
78
No.
9

Table
1,
Susceptibility
of
seven
species
of
Passifloraceae
to
Septoria
passiflorae
No. of
plants
Disease
Passifloraceae
species
inoculated
index"
Passiflora
laurifolia
P.
ligularis
P.
suberosa
P.
edulis
P.
e.flavicarpa
P.
foetida
P.
tripartita
var.
tripartita
8
8
8
8
8
8
8
0
0
0
0
0
1
3
aO
=
No
symptoms,
1 — few
chlorotic
lesions
per
leaf
without
necrotic
centers,
2 = one
to
five
lesions
per
leaf
with
necrotic
centers,
3
=
more
than
five
lesions
per
leaf
with
acute
chlorosis,
blight,
and
severe
defoliation.
DISCUSSION
Septoria fungi have been well docu-
mented
as
host-specific
pathogens.
In
some
cases,
pathogenicity
is
limited
to
a
single
host
species
(e.g.,
S.
tritici
Roberge
in
Desmaz.,
which consists
of
several forma speciales attacking single
hosts),
or to
closely related host species
within
a
genus (e.g.,
S.
septulata
Beach.,
S.
helianthi
Ellis
&
Kellerm,
5,
lactucae
Pass.,
S.
cirsii
Niessl,
S.
polygonorum
Desmaz,,
and S.
apiicola
Speg.),
or to
a few
species
in
closely related genera
within
a
family
of
plants (e.g.,
S,
lactucicola
Ellis
& G.
Martin,
5.
scrophulariae
Peck,
S.
malvicola
Ellis
&
G,
Martin,
and
S.
lycopersici Speg.)
(1,3,4).
Our
study supports
the
evidence
that Septoria
spp,
are
highly specialized.
Therefore, they
are
promising fungi
for
bioherbicide exploitation (12).
Pathogenicity tests confirmed
S.
passiflorae
isolated from diseased
banana
poka leaves from Colombia
as
an
aggressive pathogen
of P. t.
tripartita
in
Hawaii.
The
probability
for
success
of
this fungus
as a
biocontrol agent
for
banana poka appears excellent, primar-
ily
because this pathogen
is
restricted
in
its
pathogenicity
to a few
closely related
host species within
the
genus
Passiflora,
Host range studies have demonstrated
that
5.
passiflorae isolated from
banana
poka
leaves from Aldana,
Narifio,
Colombia,
is
pathogenic
to P. t.
tripartita
and P.
foetida,
two
introduced weeds
of
importance
in
Hawaii.
It
does
not
infect
the
important commercial crops
P.
edulis
and
P.
e.
flavicarpa.
The
other species
of
Passiflora tested
are not
susceptible
and
have
no
agricultural
significance
in
Hawaii.
P.
manicata
Juss. (red passion
fruit),
P.
pulchella
Kunth
(two-lobed
passion fruit),
P.
quadrangular
is
L.
(giant granadilla),
P.
subpeltata
Ort.
(white
passion flower),
and P,
vitifolia
Kunth were
not
tested because they have
not
become naturalized.
When released
on
selected banana
poka sites
in
Kauai, Maui,
and
Hawaiian
forests,
the S,
passiflorae isolated from
banana
poka
lesions from
Aldana,
Narifio,
Colombia,
is
expected
to
reduce
the
growth
and
spread
of
banana poka
significantly.
This fungus also infects
P.
foetida,
a
weedy species found
in
rocky
outcrops
and
noncultivated land. Since
there
are no
native populations
of
Pas-
sifloraceae
in
Hawaii (8),
and
since
all
members
of the
family
are
introduced
plants,
we
recommend
the
release
of
this
pathogen from Hawaiian quarantine
for
field
testing
at
selected forest sites.
ACKNOWLEDGMENTS
We
thank
the
State
of
Hawaii Department
of
Land
and
Natural Resources
for
partially
funding
this
research.
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Plant
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1994
885