FLORIDA STATE HORTICULTURAL SOCIETY, 1973
418
flower bud initiation in this particular Ixora cul-
tivar. Other possible applications of this material
need to be investigated, especially on viny species.
The potential for this chemical in ornamental
horticulture is tremendous.
nials. Plant Growth Substances, 1970. Ed. by Denis J. Carr.,
Springer-Verlag, Berlin, Heidelberg, New York. pp. 758-766.
2. Phillips, I. D. J. and R. L. Jones. 1964. Gibberellin-like
activity in bleeding sap of root systems of Helianthus annuus detected by a new dwarf pea epicotyl assay and other
methods. Planta 63:269-278.
3. Reid, D. M. and A. Crozier. 1972. Stimulation of the
levels of gibberellin-like substances by the growth retardants
CCC and AMO 1618. Plant Growth Substances, 1970. Ibid.,
pp. 420-427.
Literature Cited
1. Goldschmidt, E. E. and S. P. Monselise. 1972. Hormonal
control of flowering in citrus and some other woody peren
4.
and D. J. Carr. 1967. Effects of a dwarfing
compound, CCC, on the production and export of gibberellinlike substances by root systems. Planta 73:1-11.
COLLETOTRICHUM NEEDLE NECROSIS OF
NORFOLK ISLAND PINE
W. H. Ridings
Materials and Methods
FDACS, Division of Plant Industry
The isolate of Colletotrichum used in this study
was derived from naturally infected needles of a
Gainesville
young tree of A. heterophylla. Isolations on potato
Abstract A needle necrosis of Norfolk Island
pine (Araucaria heterophylla), commonly known
in the nursery trade as A. excelsa, is reported for
the first time. Seedlings inoculated with a conidial
suspension of the fungus Colletotrichum showed
necrotic areas only on the needles at the branch
tips after 10 to 14 days. Conidia from acervuli
on infected needles measured 14.5 x 4.0 ^ and
conidia produced on setae in the acervuli meas
ured 12.7 x 3.5 ju,. This species of Colletotrichum
coincides with the description for C. derridis.
Chemical control was obtained with Dithane M-45,
Benlate, Daconil, and Kocide 101.
Norfolk
Island pine, Araucaria
heterophylla
(Salisb.) Franco, commonly known in the nursery
trade as Araucaria excelsa R. Br., is a popular
dark green, pyramidal, evergreen tree grown in
lower central Florida and southward (3). Rela
tively few diseases of Norfolk Island pine have
been reported. Fungi attacking this host include
Phytophthora parasitica Dastur (2), Cryptospora
longispora Servazzi (7), and Coniothyrium palidofuscum Sacc. (8). Recently, the fungus Colletotri
chum has been found associated with an unreported
disease of the needles of seedlings and young trees
in Florida nurseries. This paper reports the identi
fication, pathogenicity, and control of this fungus.
dextrose agar (PDA) were made either by pick
ing conidia from the spore masses on the infected
needles or by plating on PDA pieces of necrotic
needle tissue following surface sterilization with
0.1% sodium hypochlorite for 2 min and rinsing
in sterile distilled water.
Conidia were produced abundantly on PDA in
glass petri plates by maintaining cultures under
alternating 12 hrs dark and 12 hrs of fluorescent
light at room temperature (ca 22-25 C) for 7-10
days. Inoculum was prepared by making a conidial
suspension from culture, filtering through doublelayered cheesecloth, and diluting the conidia with
sterile tap water to 5-10 x 105 conidia/ml as meas
ured with the hemacytometer. The inoculum was
atomized on the branches of young trees ca 2 ft
tall. The plants were then covered with a plastic
bag and placed in a mist chamber.
Fungicides tested for control of needle necrosis
were Benlate (% lb/100 gal), Dithane M-45
(1 % lb/100 gal), Daconil (1 % lb/100 gal), and
Kocide 101 (1 Y2 lb/100 gal). The fungicides were
applied at 7-day and 1-day intervals prior to inocu
lation of the branches and needles. Plyac (0.2 ml/
liter) was added to the fungicide preparations.
Results
Pathogenicity Tests
Inoculated branches
Contribution No. 360, Bureau of Plant Pathology.
developed necrotic
spots
and complete necrosis of the needles at the tips of
RIDINGS: NORFOLK ISLAND PINE NECROSIS
419
the branches after 10-14 days in the mist chamber
(Fig.
1).
Infection occurred only on young de
veloping needles. These symptoms were obtained
in three separate trials with three plants per trial.
No infection developed on non-inoculated plants
used
as
controls.
Isolations
from
the
necrotic
needles consistently yielded the Colletotrichum used
in the inoculations.
Removal
of infected plants
from the mist chamber to the greenhouse bench
where the foliage remained dry resulted in the
resumption of healthy needle development at the
branch tips.
Identification of Causal Fungus
The presence of acervuli, setae, and one-celled
hyaline conidia on infected needles identified this
fungus as a species of Colletotrichum. In many
instances, artificially infected needles taken from
the mist chamber showed acervuli without setae.
Upon further incubation of these necrotic needles
under dry conditions, conidia were produced on the
tips of setae formed within the acervuli (Fig. 2).
This environmental effect on setae formation has
been noted by Ikata (4).
Fig. 2. Conidia borne at tips of setae of Colletotrichum
from A. heterophylla
(X347).
Conidia formed in acervuli on infected stems
measured 11.5-18.4 x 2.3-4.6 ^ (mean 14.5 x 4.0^)
while those produced in culture on PDA measured
14.8-19.9 x 4.9
p.
(mean
16.7 x 4.9^).
Conidia
formed at the tips of the setae measured 8.1-16.1
x 2.3-4.6 fx (mean 12.7 x 3.5^). Thus, very small
differences were found in conidia produced by these
methods. Cultures obtained from conidia in acervuli
were morphologically indistinguishable from those
obtained from conidia on the setae. Setae were not
formed in any cultures on PDA.
Setae from infected needles were dark brown
to black with hyaline tips and measured 101.6171.5 x 3.7-4.9 fj, (mean 133 x 4.5^). No perfect
state of this isolate was found in 3-month-old cul
tures on PDA or on infected needles incubated
6-8 weeks.
The morphological characteristics of this isolate,
especially the production of conidia on the tips of
the setae, fit those described for C. derridis Van
Hcof and C. gossypii
Southworth
(1,10,12).
A
comparison of the conidia, setae, and lack of pro
duction of a perfect state indicates that the Col
letotrichum isolate from A. heterophylla coincides
with the description for C. derridis (Table 1).
Fungicide Tests
Fig:. 1. Necrotic spots on inoculated needles of A. hetero-
phylla.
Dithane M-45 gave the best control while
Daconil, Benlate, and Kocide 101 gave 85, 75, and
58% control, respectively (Table 2). No phytotoxic
effects were noted from the use of these fungicides.
FLORIDA STATE HORTICULTURAL SOCIETY, 1973
420
Table 1.
A comparison of the morphological characters of the Colletotrichum
isolate from A, heterophylla with those of two described Colletotrichum
spp.
Colletotrichum from
Morphological
A.
character
Conidia
Setae
heterophylla
C.
C,
derridis
gossypii
11.5-18.4 x 2.3-4.6u
10-21 x 4-6.5y
15-20 x 4.5-9y
(mean 14.5 x 4.0y)
(on infected needles)
(mean 15 x 5y)
Van Hoof (12)
Atkinson (1)
14.8-19.9 x 4.9y
13-20 x 4.5-8.0y
(mean 16.7 x 4.9y)
(on PDA)
(mean 16.1 x 6.6y)
John (5)
101.6-171.5 x 3.7-4.9y
20-110 x 4-6.5y
100-250y
(mean 133 x 4.5y)
(mean 60 x 5\i)
Atkinson (1)
Van Hoof
(12)
84-170 x 4-5y
(mean 133 x 4.5y)
John (5)
Perfect
state
Glomerella
Not known
Not known
gossypii Edg.
Table 2.
Effectiveness of
fungicides
as protec-
tants of A. heterophylla against infection by
Colletotrichum.
% of
infected
branch tips2
Treatment
%
of
disease
control
15
75
Daconil
9
85
Dithane M-45
(1 1/2 lb/100 gal)
1
98
25
58
59
0
0
100
Benlate
(1/2 lb/100 gal)
(1 1/2 lb/100 gal)
(1 1/2 lb/100 gal)
Check
(inoculated)
Check
(non-inoculated)
^Infection varied from light (1-2 needles with
spots) to severe (at least 90% of needles at
branch tips with extensive necrosis).
Data repre
sent average of all branch tips on A branches per
3
trees
This study reports for the first time a species
of Colletotrichum which causes a needle necrosis
of A. heterophylla. The morphology of this isolate
of Colletotrichum coincides with that described for
C. derridis which causes leaf spotting of Derris
elliptica Benth (6,11), Hevea rubber (5), and
Manihot glazioii Muell. Arg. (5). In Florida, an
undescribed species of Colletotrichum which is
similar in morphology to C. derridis and C. gos
sypii causes leaf spotting and stem canker of
Stylosanthes spp. (9).
Kocide 101
tree for
Discussion
in 2
experiments.
Although fungicidal control appears feasible,
an additional method which growers might con
sider is to minimize excessively long periods of
moisture on the foliage. This was demonstrated in
this study by the development of healthy needles
on infected plants removed from the mist chamber
to greenhouse benches where wetting of the needles
was minimal. The new growth on vigorously de
veloping plants is susceptible to infection and thus
should be protected under conditions favorable for
disease development.
KNAUSS: SYNGONIUM RHIZOCTONIA BLIGHT
Literature Cited
1. Atkinson, G. F. 1891. Anthracnose of cotton. J. Mycol.
6:173-178.
2. Bazan DeSegura, C. 1951. Plant diseases new to Peru.
Plant Dis. Rep. 35(10) :465-466.
3. Bush, C. S. 1969. Flowers, shrubs, and trees for Flor
ida homes. Fla. Dept. Agr. & Consum. Serv. Bull. 195. 179 p.
4. Ikata, S. 1936. The function and formation of setae on
some Anthracnose fungi. Agr. and Hort. 5:360-362 [Rev.
Appl. Mycol. 16:410-411 (Abstr.)].
5. John, K. P. 1952. A hitherto undescribed leaf disease
of Hevea rubber caused by a species of Colletotrichum. J.
Rubber Res. Inst., Malaya 14(278) :11-19.
6. Ling, L. 1951. On the occurrence of Colletotrichum
derridis in Taiwan. Plant Dis. Rep. 35(1):13-15.
7. Servazzi, O. 1938. Intorno ad un caso di disseccamenti
osservuti su Araucaria. (On a case of drying-up observed on
Araucaria.)
Boll.
Lab.
Sper.
421
R.
Ossv.
Fitopath.,
Torino
15(1-2) :34-47 [Rev. Appl. Mycol. 17:748 (Abstr.)].
8.
. 1942. Brevi note su alcune non communi
malathe fungine di piante ornamentali. (Brief notes on some
uncommon fungal diseases of ornamental plants.) Boll. Lab.
Sper. R. Ossv. Fitopath., Torino 18(1-4): 86-112 [Rev. Appl.
Mycol. 25:451 (Abstr.)].
9. Sonoda, R. M., A. E. Kretschner, Jr., and J. B. Biolmann. 1973. Colletotrichum leaf spot and stem canker of
Stylosanthes spp. Trop. Agr. (Trinidad):: (In press).
10. Southworth, E. A. 1891. Anthracnose of cotton.
Mycol. 6:100-105.
J.
11. Van Hoof, H. A. 1950a. Cause and control of a leaf
disease in Derris elliptica Benth. Contrib. Gen. Agr. Res. Sta.
(Bogor) 115:1-11 [Rev. Appl. Mycol. 31:86 (Abstr.)].
._ 12-.
• 1950b. A new species of Colletotrichum
(Fungi Imperfecti). Bull. Gardens, Buitenz (formerly Bull.
Jard. Bot., Buitenz) (Ser. Ill) 18(4) :473-478.
RHIZOCTONIA BLIGHT OF SYNGONIUM
J. F. KNAUSS
IFAS Agricultural Research Center
Apopka
Abstract. The fungus, Rhizoctonia solani
Kuehn, was observed in foliage nurseries causing
a serious disease of cuttings, leaves and seedlings
in cultivars of Syngonium podophyllum Schott. In
experiments with S. podophyllum 'Green Gold',
R. solani, produced both a severe cutting decay
and a symptom on the first emerging leaf of
many surviving cuttings which previously had
been attributed to insect feeding. In several tests,
the soil-applied fungicides benomyl and thiabendazole were found particularly effective for control.
and aerial roots. Both types of damage are shown
in Fig. 1. The prominent reddish brown hyphae
of the pathogen are generally visible on the
propagative media and infected tissue. If a cutting
survives infection and roots, the pathogen may at
tack the emerging shoot and leaf with disease de
velopment ceasing after the leaf emerges through
the soil and unfurls. This type of infection appears
as ragged holes within and along the leaf margin
and/or within the leaf as small reddish brown
spots with a chlorotic margin (Fig. 2).
Materials and Methods
The R. solani culture used in Tests 1-5 was
isolated from S. podophyllum, and that used in
Cultivars of Syngonium podophyllum Schott
(nephthytis), popular as ornamental foliage plants,
are
propagated by cuttings and seed. Several
phytopathogens are reported to attack nephthytis
(2,5,6,7) and one, Rhizoctonia solani Kuehn, was
observed over a 4 year period, to cause considerable
losses of cuttings and seedlings during propagation.
These investigations were undertaken to re
produce and describe the disease caused by R.
solani and to evaluate fungicides for its control.
Rhizoctonia solani, under warm to hot, moist
conditions, causes a serious decay and collapse of
recently-planted cuttings. On young succulent cut
tings, the grayish brown to black rot progresses
from the cutting tip downward with a line of
demarcation usually evident between healthy and
diseased tissue. On more mature cuttings, infec
tion usually occurs in the area of the leaf sheath
Florida Agricultural Experiment Stations Journal Serie
No. 5174.
Fig. 1. Rhizoctonia solani infection of nephthytis cuttings
—with rot initiated at top of cutting: and in the nodal area.