• TABLE OF CONTENTS
HIDE
 Copyright
 Title Page
 The disease
 Casual organism
 The casual organism in relation...
 Conclusions
 Literature cited






Group Title: Agricultural Experiment Station Bulletin no. 186
Title: Thread blight
CITATION PAGE IMAGE ZOOMABLE
Full Citation
STANDARD VIEW MARC VIEW
Permanent Link: http://ufdc.ufl.edu/UF00026404/00001
 Material Information
Title: Thread blight a fungous disease of plants caused by Corticium stevensii Burt.
Series Title: Bulletin - Florida Agricultural Experiment Station Bulletin ; 186
Physical Description: p. 139-162 : ill. ; 23 cm.
Language: English
Creator: Weber, George F ( George Frederick ), b. 1894
Publisher: University of Florida Agricultural Experiment Station
Place of Publication: Gainesville Fla
Publication Date: 1927
 Subjects
Subject: Fungal diseases of plants -- Florida   ( lcsh )
Corticium   ( lcsh )
Genre: bibliography   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
non-fiction   ( marcgt )
 Notes
Statement of Responsibility: by G.F. Weber.
Bibliography: Bibliography: p. 161-162.
General Note: Cover title.
Funding: Bulletin - Florida Agricultural Experiment Station Bulletin ; 756
 Record Information
Bibliographic ID: UF00026404
Volume ID: VID00001
Source Institution: Marston Science Library, George A. Smathers Libraries, University of Florida
Holding Location: Florida Agricultural Experiment Station, Florida Cooperative Extension Service, Florida Department of Agriculture and Consumer Services, and the Engineering and Industrial Experiment Station; Institute for Food and Agricultural Services (IFAS), University of Florida
Rights Management: All rights reserved, Board of Trustees of the University of Florida
Resource Identifier: aleph - 000923493
oclc - 18172778
notis - AEN4044

Table of Contents
    Copyright
        Copyright
    Title Page
        Title Page 1
        Title Page 2
    The disease
        Page 143
        Geographical distribution
            Page 143
        Host range
            Page 144
        Economic importance
            Page 144
            Page 145
        Symptoms
            Page 146
    Casual organism
        Page 147
        Taxonomy
            Page 147
            Page 148
        Morphology
            Page 149
            Page 150
            Page 151
            Page 152
        Physiology
            Page 153
        Pathogenicity
            Page 153
            Page 154
    The casual organism in relation to the production of the disease
        Page 155
        Source of inoculum
            Page 156
        Longevity
            Page 157
        Overwintering
            Page 158
        Congrol
            Page 158
            Page 159
    Conclusions
        Page 160
    Literature cited
        Page 161
        Page 162
Full Text





HISTORIC NOTE


The publications in this collection do
not reflect current scientific knowledge
or recommendations. These texts
represent the historic publishing
record of the Institute for Food and
Agricultural Sciences and should be
used only to trace the historic work of
the Institute and its staff. Current IFAS
research may be found on the
Electronic Data Information Source
(EDIS)

site maintained by the Florida
Cooperative Extension Service.






Copyright 2005, Board of Trustees, University
of Florida







SBulletin 186


UNIVERSITY OF FLORIDA
AGRICULTURAL EXPERIMENT STATION




THREAD BLIGHT

A Fungous Disease of Plants Caused by
Corticium Stevensii Burt.

By G. F. WEBER I y


Fig. 100.-Sclerotia on year-old pecan (Hicoria pecan) twigs.

TECHNICAL BULLETIN

Bulletins will be sent free upon application to the
Agricultural Experimesnt Station
GAINESVILLE, FLORIDA


March, 1927i







BOARD OF CONTROL
P. K. YONGE, Chairman, Pensacola
E. L. WARTMANN, Citra
E. W. LANE, Jacksonville
A. H. BLENDING, Leesburg
W. B. DAVIS, Perry
J. T. DIAMOND, Secretary, Tallahassee
J. G. KELLUM, Auditor, Tallahassee
STATION STAFF
WILMON NEWELL, D. Sc., Director
JOHN M. SCOTT. B. S., Vice Director and Animal Industrialist
SAM T. FLEMING, A. B., Assistant to Director
J. R. WATSON, A. M. Entomologist
ARCHIE N. TISSOT, M. S., Assistant Entomologist
H. E. BRATLEY, M. S. A., Asst. in Entomology
R. W. RUPRECHT, Ph. D., Chemist
R. M. BARNETTE, Ph. D., Assistant Chemist
C. E. BELL, M. S. Assistant Chemist
HOUSDEN L. MARSHALL, M. S., Assistant Chemist
JACKSON D.. HESTER, M. S., Assistant Chemist
J. M. COLEMAN, B. S., Assistant Chemist
0. F. BURGER, D. Sc., Plant Pathologist
G. F. WEBER, Ph. D., Associate Plant Pathologist
J. L. SEAL, M. S., Assistant Plant Pathologist
ROBERT E. NOLEN, M. S. A., Lab. Asst. in Plant Pathology
K. W. LOUCKS, A. B., Lab. Asst. in Plant Pathology
ERDMAN WEST, B. S., Lab. Asst. in Plant Pathology
D. G. A. KELBERT, Field Asst. in Plant Pathology
W. E. STOKES, M. S., Agronomist
W. A. LEUKEL, Ph. D., Assistant Agronomist
A. F. CAMP, Ph. D., Associate Horticulturist
HAROLD MOWRY, Assistant Horticulturist
G. H. BLACKMON, B. S.-A., Pecan Culturist
M. R. ENSIGN, M. S., Truck Horticulturist
M. N. WALKER, Ph. D., Assistant Cotton Specialist
W. A. CARVER, Ph. D., Assistant Cotton Specialist
EDGAR F. GROSSMAN, M. A., Assistant Entomologist, Cotton Investigations
RAYMOND CROWN, B. S. A., Field Asst., Cotton Investigations
A. L. SHEALY, D. V. M., Veterinarian
D. A. SANDERS, D. V. M., Assistant Veterinarian
C. V. NOBLE, Ph. D., Agricultural Economist
BRUCE MCKINLEY, B. S. A., Assistant Agricultural Economist
H. G. HAMILTON, M. S., Assistant Agricultural Economist
OUIDA DAVIS ABBOTT, Ph. D., Head. Home Economics Research
LEONARD W. GADDUM, Ph. D., Assistant in Home Economics
IDA KEELING CRESAP, Librarian
J. FRANCIS COOPER, B. S. A., Editor
,RUBY NEWHALL, Secretary
HENRY ZEIGLER, Farm Foreman
W. B. TISDALE, Ph. D., Plant Pathologist, in charge Tobacco Experiment
Station (Quincy)
Ross F. WADKINS, M. S., Lab. Asst. in Plant Pathology (Quincy)
JESSE REEVES, Foreman Tobacco Experiment Station (Quincy)
L. O. GRATZ, Ph. D., Assistant Plant Pathologist (Hastings)
A. S. RHOADS, Ph. D., Assistant Plant Pathologist (Cocoa)
A. N. BROOKS, Ph. D., Assistant Plant Pathologist (Plant City)
STACY O. HAWKINS, Field Asst. in Plant Pathology (Miami)
J. H. JEFFERIES, Superintendent Citrus Experiment Station (Lake Alfred)
W. A. KUNTZ, A. M., Assistant Plant Pathologist (Lake Alfred)
GEO. E. TEDDER, Foreman, Everglades Experiment Station (Belle Glade)
R. V. ALLISON, Ph. D., Soils Specialist (Belle Glade)
J. H. HUNTER, M. S., Assistant Agronomist (Belle Glade)
FRED W. WALKER, Assistant Entomologist (Monticello)

K. H. GRAHAM, Auditor.
RACHEL MCQUARRIE, Assistant Auditor








THREAD BLIGHT
A Fungous Disease of Plants Caused by
Corticium stevensii Burt.
By G. F. WEBER
The disease herein reported occurs on numerous plants in
Florida and is caused by the fungus Corticium stevensii Burt,
spoken of by Nowell (10*) as thread blight. Fawcett (7) men-
tioned a similar disease which he designated as leaf spot or
thread blight on coffee. It has been observed in Florida since
1920.
THE DISEASE
GEOGRAPHICAL DISTRIBUTION

The disease was first reported from Brazil where it was orig-
inally described by Noack (9) in 1898. Nowell (10) reports
the disease common in the West Indies and widely distributed
over the world, especially in the humid places in the tropics.
Cook (4) reports a similar disease on tea in Java. Burt (3)
reports that the disease has been found commonly in Brazil and
Trinidad. In the United States its earliest occurrence was
noted by Quaintance (12) who received "specimens from both
Georgia and Florida. Stevens and Hall (19, 20) reported the
disease as common in North Carolina, West Virginia and Ala-
bama. Smith and Stevens (15) report it common in the moun-
tainous sections of the above enumerated states. Hesler and
Whetzel (8) state that the disease has been found in the Appa-
lachian mountain valleys extending from Maine to Florida, be-
ing most important in West Virginia, North Carolina, Georgia,
Alabama and Florida. They intimate that it was introduced
from Brazil.
In Florida the first record made of the occurrence of this dis-
ease was more than 25 years ago when a specimen was sent to
Quaintance (12) from the vicinity of Lake City. Since that
time specimens have been collected at Bluefield by Burger (1)
in the south central portion of the state about equally distant
between the north end of Lake Okeechobee and the Atlantic
Coast, and at Gainesville, about 40 miles south of Lake City.
It is widely distributed in Florida but rather localized in its
severity.

*Reference is made by numbers in parentheses to "Literature Cited"
at the close of this bulletin.








THREAD BLIGHT
A Fungous Disease of Plants Caused by
Corticium stevensii Burt.
By G. F. WEBER
The disease herein reported occurs on numerous plants in
Florida and is caused by the fungus Corticium stevensii Burt,
spoken of by Nowell (10*) as thread blight. Fawcett (7) men-
tioned a similar disease which he designated as leaf spot or
thread blight on coffee. It has been observed in Florida since
1920.
THE DISEASE
GEOGRAPHICAL DISTRIBUTION

The disease was first reported from Brazil where it was orig-
inally described by Noack (9) in 1898. Nowell (10) reports
the disease common in the West Indies and widely distributed
over the world, especially in the humid places in the tropics.
Cook (4) reports a similar disease on tea in Java. Burt (3)
reports that the disease has been found commonly in Brazil and
Trinidad. In the United States its earliest occurrence was
noted by Quaintance (12) who received "specimens from both
Georgia and Florida. Stevens and Hall (19, 20) reported the
disease as common in North Carolina, West Virginia and Ala-
bama. Smith and Stevens (15) report it common in the moun-
tainous sections of the above enumerated states. Hesler and
Whetzel (8) state that the disease has been found in the Appa-
lachian mountain valleys extending from Maine to Florida, be-
ing most important in West Virginia, North Carolina, Georgia,
Alabama and Florida. They intimate that it was introduced
from Brazil.
In Florida the first record made of the occurrence of this dis-
ease was more than 25 years ago when a specimen was sent to
Quaintance (12) from the vicinity of Lake City. Since that
time specimens have been collected at Bluefield by Burger (1)
in the south central portion of the state about equally distant
between the north end of Lake Okeechobee and the Atlantic
Coast, and at Gainesville, about 40 miles south of Lake City.
It is widely distributed in Florida but rather localized in its
severity.

*Reference is made by numbers in parentheses to "Literature Cited"
at the close of this bulletin.






Florida Agricultural Experiment Station


HOST RANGE
Noack (9) first found the disease on leaves and branches of
pear and quince. Quaintance (12) collected the disease on
apple and pear trees. Sheldon (14) found it on apple, pear and
plum and stated that it had been reported to him on currant,
gooseberry and cherry. Nowell (10) reported it common on
cocoa and nutmeg in the West Indies. Fawcett (7) reported it
on guava, sour orange, hibiscus, croton, dish rag gourd and the
West Indian gherkin. Hesler and Whetzel (8) add to this list
lilac and snowball. Burger (1) states that the disease has been
found on pecan and grapefruit. The LeConte pear was the first
tree reported attacked by this fungus in Florida (12). It has
been found more or less common on sand pears (Pyrus com-
munis). At Gainesville it has been collected on Virginia
creeper (Ampelopsis quinquefolia), plum (Prunus angustifolia),
Pistacia chinensis, rose (Rosa sp.), soapberry (Sapindus itil's),
pomegranate (Punica granatum), persimmon (Diospyros kaki),
jujube (Zizyphus mauritiana), chinaberry (Melia azedarach),
morning-glory (Ipomoea triloba), mu-oil tree (Aleurites mon-
tana), fig (Ficus qarica) and the tung-oil tree (Aleurites
fordii.) (Fig. 101.)
Authentic specimens have been taken from all the above men-
tioned hosts and the disease has been observed during one or
more growing seasons on most of them. Thus the host range
previously reported is pear, quince, apple, plum, gooseberry,
currant, cocoa, nutmeg, guava, sour orange, hibiscus, croton,
gourd, gherkin, lilac and snowball. Additional hosts reported
here for the first time are pecans, fig, Virginia creeper, pist-
ache, soapberry, rose, pomegranate, persimmon, jujube, china-
berry, morning-glory, mu-oil tree, tung-oil tree, and grapefruit.

ECONOMIC IMPORTANCE

Quaintance (12) stated that 50 percent defoliation resulted
from the attacks of this disease. Eustace (5) stated that the
damage was not large. It was reported to be worst on neglect-
ed trees by Smith and Stevens (15) and that under these cir-
cumstances it caused considerable defoliation. Hesler and
Whetzel (8) stated that a large number of twigs were indirect-
ly killed and the attacked trees devitalized by the loss of foliage.
Stevens and Hall (18) observed that excessive humidity aided






Florida Agricultural Experiment Station


HOST RANGE
Noack (9) first found the disease on leaves and branches of
pear and quince. Quaintance (12) collected the disease on
apple and pear trees. Sheldon (14) found it on apple, pear and
plum and stated that it had been reported to him on currant,
gooseberry and cherry. Nowell (10) reported it common on
cocoa and nutmeg in the West Indies. Fawcett (7) reported it
on guava, sour orange, hibiscus, croton, dish rag gourd and the
West Indian gherkin. Hesler and Whetzel (8) add to this list
lilac and snowball. Burger (1) states that the disease has been
found on pecan and grapefruit. The LeConte pear was the first
tree reported attacked by this fungus in Florida (12). It has
been found more or less common on sand pears (Pyrus com-
munis). At Gainesville it has been collected on Virginia
creeper (Ampelopsis quinquefolia), plum (Prunus angustifolia),
Pistacia chinensis, rose (Rosa sp.), soapberry (Sapindus itil's),
pomegranate (Punica granatum), persimmon (Diospyros kaki),
jujube (Zizyphus mauritiana), chinaberry (Melia azedarach),
morning-glory (Ipomoea triloba), mu-oil tree (Aleurites mon-
tana), fig (Ficus qarica) and the tung-oil tree (Aleurites
fordii.) (Fig. 101.)
Authentic specimens have been taken from all the above men-
tioned hosts and the disease has been observed during one or
more growing seasons on most of them. Thus the host range
previously reported is pear, quince, apple, plum, gooseberry,
currant, cocoa, nutmeg, guava, sour orange, hibiscus, croton,
gourd, gherkin, lilac and snowball. Additional hosts reported
here for the first time are pecans, fig, Virginia creeper, pist-
ache, soapberry, rose, pomegranate, persimmon, jujube, china-
berry, morning-glory, mu-oil tree, tung-oil tree, and grapefruit.

ECONOMIC IMPORTANCE

Quaintance (12) stated that 50 percent defoliation resulted
from the attacks of this disease. Eustace (5) stated that the
damage was not large. It was reported to be worst on neglect-
ed trees by Smith and Stevens (15) and that under these cir-
cumstances it caused considerable defoliation. Hesler and
Whetzel (8) stated that a large number of twigs were indirect-
ly killed and the attacked trees devitalized by the loss of foliage.
Stevens and Hall (18) observed that excessive humidity aided






Bulletin 186, Thread Blight


Fig. 101.-Some new hosts of Corticium stevensii Burt.
A. Fig (Ficus curica) B. Pistache (Pistacia chinensis)
C. Pecan (Hicoria pecan) D. Pomegranate (Punica grana-
E. Plum (Prunus angustifolia) turn)
G. Morning Glory (Ipomoeae tri- F. Soapberry (Sapindus utilis)
loba) H. Jujube (Zizyphus mauritiana)
I. Chinaberry (Melia azaderack) J. Mu-oil tree (Aleuroides mon-
tana)


Off







Florida Agricultural Experiment Station


the disease in its destructiveness in specific Appalachian val-
leys. Burger (1) reports the disease on pear causing 50 per-
cent defoliation and slight damage to pecan.
In localities where it has been observed for a number of years
few serious developments have been observed. On individual
trees it has caused 50 to 60 percent defoliation in a few weeks
and in such instances the killing back of portions of the current
season's growth has resulted. Over a period of three or four
years it has spread undoubtedly from a single source at Gaines-
ville to a large number of different hosts. The fruits of citrus
and tung-oil trees occasionally have been found overgrown with
the fungus. Pecan and pomegranate have suffered because of
defoliation.
SYMPTOMS

The most common symptom of the disease in Florida agree
with descriptions given by Noack (9), Cook (4), Nowell (10),
Fawcett (6), Hesler and Whetzel (8), Stevens and Hall (18)
and Burger (1), namely the matting together of the killed
leaves. They become brown or black and cling to each other
and to the twigs by fungous threads or strands. These strands
are easily seen on the under side of twigs; petioles and veins
in the blades. The symptoms are very characteristic of the
disease.
The fungus is usually'on the lower half of the twigs, and has
been observed to be more prominent on the west side of verti-
cal twigs. In late summer the fungus usually involves -the
branches and twigs to their entirety and in such instances
catues complete defoliation. It is most abundant on current
season's growth and diminishes in prominence on year-old and
two-year-old branches. Rapidly following a dried condition the
leaves appear scalded and become slightly lighter green in color,
soon turning brown. Occasionally only portions of the lower
surface of the blades are covered with the mycelium when the
first dead areas are evident. Following the appearance of the
dead area the whole blade is rapidly involved, becomes dry and
hard, wrinkles and droops, finally becoming detached. Such
dead leaves usually persist for indefinite periods by means of
the rhizomorphic strands. These groups of hanging leaves are
finally detached by wind and rain.
The development of sclerotia on the blades of the leaves has







Bulletin 186, Thread Blight


seldom been observed. On the petioles, however, by actual
count it was found that more than a hundred sclerotia had de-
veloped over a distance of 6 inches. These sclerotia were with-
out exception on one side of the petioles. The rhizomorphs on
tung-oil and citrus advance from the twigs to the stem of the
fruits hence to the fruits. They do not spread out over the sur-
face of the fruits as is usual on the leaf blade but rather develop
into a few undulating strands terminating in a number of seri-
ately arranged sclerotia of irregular size and shape.
Description: On the youngest growth the rhizomorphs and
sclerotia develop abundantly. Often the strands are so thick
and uniform as to form a soft felty growth over the. surface of
the twig. They are often ridged, undulating and uneven. On
old leaf scars and near the tips of twigs where bud scales are
forming the hyphae and sclerotia develop so profusely that a
sort of stroma is formed covering these parts completely. The
closer to the tips of the branches the observations are made the
denser the hyphal strands become and the more numerous and
irregular in size are the sclerotia. The rhizomorphs always
branch off from the petioles to the lower surface of the blades.
One of the several strands will spread out on the leaf blade be-
coming almost invisible in fineness. Often these strands will
follow the main veins for a considerable distance before dis-
persing over the blade. Strands are very seldom formed be-
tween the veins of the leaf. The secondary strands cover the
lower surface of the leaf with a fine network of threads, dis-
tinctly visible in reflected sunlight as very fine, uniform, glist-
ening, cobwebby, brown, silklike threads. The lower surface
is often entirely covered before any detrimental effect to the
tissue is detected.

CAUSAL ORGANISM

TAXONOMY

The fungus in question was described by Noack (9) as it ap-
peared in Brazil and he proposed the name of Hypochnopsis
ocholeuca. Saccardo (13) gives the Latinized form of the spe-
cies described by Noack listing it as Hypochnus oirril,'ocli, e
Noack. This binomial has been. used in reference to this fun-
gus by Nowell (10), Stevens and Hall (20) and Burt (3).
However, there has been some question as to the difference be-







Bulletin 186, Thread Blight


seldom been observed. On the petioles, however, by actual
count it was found that more than a hundred sclerotia had de-
veloped over a distance of 6 inches. These sclerotia were with-
out exception on one side of the petioles. The rhizomorphs on
tung-oil and citrus advance from the twigs to the stem of the
fruits hence to the fruits. They do not spread out over the sur-
face of the fruits as is usual on the leaf blade but rather develop
into a few undulating strands terminating in a number of seri-
ately arranged sclerotia of irregular size and shape.
Description: On the youngest growth the rhizomorphs and
sclerotia develop abundantly. Often the strands are so thick
and uniform as to form a soft felty growth over the. surface of
the twig. They are often ridged, undulating and uneven. On
old leaf scars and near the tips of twigs where bud scales are
forming the hyphae and sclerotia develop so profusely that a
sort of stroma is formed covering these parts completely. The
closer to the tips of the branches the observations are made the
denser the hyphal strands become and the more numerous and
irregular in size are the sclerotia. The rhizomorphs always
branch off from the petioles to the lower surface of the blades.
One of the several strands will spread out on the leaf blade be-
coming almost invisible in fineness. Often these strands will
follow the main veins for a considerable distance before dis-
persing over the blade. Strands are very seldom formed be-
tween the veins of the leaf. The secondary strands cover the
lower surface of the leaf with a fine network of threads, dis-
tinctly visible in reflected sunlight as very fine, uniform, glist-
ening, cobwebby, brown, silklike threads. The lower surface
is often entirely covered before any detrimental effect to the
tissue is detected.

CAUSAL ORGANISM

TAXONOMY

The fungus in question was described by Noack (9) as it ap-
peared in Brazil and he proposed the name of Hypochnopsis
ocholeuca. Saccardo (13) gives the Latinized form of the spe-
cies described by Noack listing it as Hypochnus oirril,'ocli, e
Noack. This binomial has been. used in reference to this fun-
gus by Nowell (10), Stevens and Hall (20) and Burt (3).
However, there has been some question as to the difference be-







Florida Agricultural Experiment Station


Fig. 102.-Fungus in virulent condition on pear (Pyrus betulaefolia).

tween this fungus described by Noack and a similar fungus,
Pellicularia koleroga, found on coffee in Porto Rico, India, Col-
umbia and Venezuela as described by Cook in 1876 and Fawcett


;ur


cl..







Bulletin 186, Thread Blight


(6). Burt (3) examined material of the two above-mentioned
organisms, broadened the description of the fungus on coffee,
designating it as Corticium koleroga (Cook) V. Hohn., and list-
ed Pellicularia koleroga as a synonym. Hypochnopsis ochro-
leuca Noack, the original name of the pear fungus was discard-
ed, the fungus was redescribed and listed as Corticium stevensii
Burt. Hypochnopsis ochlroleuca Noack and Hypochnus ochro-
leucus Noack are listed as synonyms. He stated that Corticium
stevensii differed from Corticium koleroga in that the former
produced thick dark colored felty fructifications which he desig-
nated as sclerotia. According to Burt (2) they are both classi-
fied in the Telephoraceae.
Telephoraceae (key)
1. Cystidia present Peniophora
1. Cystidia absent 2.
2. spores colored Hypochnus
2. spores hyaline Corticium
The organism found in Florida is a Corticium according to
the above classification, since the basidiospores are hyaline and
there is an absence of cystidia. It is Corticium stevensii rather
than Corticium koleroga according to Burt's classification and
also according to the uses of these terms by Nowell (10) and
Stevens (16), in that there are numerous sclerotia present upon
the twigs, branches and petioles of the infected parts of the
host plant. According to the above information the writer con-
cludes that the hosts showing the disease are attacked by the
same fungus, namely Corticium stevensii Burt.

MORPHOLOGY
Mycelium: The mycelium is divided into two distinct classes
for convenience in description and in reference. The first type
consists of rhizomorphic strands growing lengthwise of the
twigs and petioles. These strands are described very carefully
by Noack (9) who states that they are delicate white or yellow-
ish, shiny threads, very compact and twisted. The rhizomorphic
strands upon reaching the leaf blade branch out until they are
practically lost to vision. According to Peltier (11) they cor-
respond in many respects to the hyphae of Rhizoctonia solani.
He states that these species are closely related although distinct.
This type of mycelium is well named migratory mycelium by







Florida Agricultural Experiment Station


Smith and Stevens (15). It is superficial and spreads out on
the leaves in an exceedingly thin layer forming a loose hymen-
ium of floccose hyphae. This reticulum varies in color from a
dirty white to pinkish buff and finally chestnut brown. The mi-
gratory strands originate from the sclerotia and grow on the
lower side of the twigs and stems toward their tips. The reticu-
lum layer can be easily stripped from the under surface of the
leaves in a fine
thin layer. It
is this layer of
hyphae that
contains the
basidia and
basidio-
spores. The
strands are
White when
young aid
brown when
old, averaging
about 6 mi-
crons in thick-
ness and coin-
tain sept a-
tions 40 to 100
Smicrons apart.
The hyphae
are profusely
branched and
Fig. 103.-Mycelium of fungus drawn from surface t h e branches
of leaf. (Camera lucida.)orm anasto-
mosis, into an endless net. No clamp connections have been
observed.
The second type of mycelium is very much smaller than the
rhizomorphic, superficial strands and is found in the host tis-
sue. Sections of young invaded leaves killed, cleared and stained
in toto with Pianeze III b and cottony blue revealed the fungus
in contrast to the host cells. The fungus grew over the epi-
dermis generally and particularly in the furrows between the
epidermal cells where the penetrating hyphae developed and
grew between the epidermal cells into the intercellular spaces







Bulletin 186, Thread Blight


of the parenchyma. The hyphae migrate almost at will among
the cells occupying the intercellular spaces. Haustoria have
not been observed. The hyphae develop abundantly in the
host tissue and are usually advancing at about the same rate
as the rhizomorphic strands on the epidermis.
Sclerotia: The sclerotia are exceedingly irregular in form,
color, size and distribution. (Fig. 100, cover.) The youngest


are of a dull white col-
or and rather downy.
As they grow older they
increase in size and be-
come at first light brown
and, when mature, dark-
en considerably to a cin-
namon brown. At ma-
turity they are brown,
compact, hard and often
shiny, although not
crusted. They are seri-
ately arranged along
the rhizomorphic
strands, varying in num-
bers with the individual
strands. Where the scle-
rotia are scattered and
not directly in line with
the rhizomorphic strands


Fig. 104.-Basidia and basidiospores of
fungus developed on leaf of tung-oil.

they are usually located over a len-


ticel or rupture in the cortex of the host plant.
The sclerotia are concave on the side in contact with the cor-
tex. The exposed surface is considerably raised, 1-2 mm. in
height and 2-12 mm. in length, averaging about twice as long
as wide. In contour they are circular to oval, occasionally al-
most oblong or linear. Their vertical dimensions are parabolic
or mound-shaped. They are solid in internal structure, being
composed entirely of mycelial strands, tightly interwoven.
When young and mature they are white and brown throughout
respectively. The change of color takes place from end to end
rather than from outside toward the center.
No fruiting structures have been associated with these sclero-
tia and their function is more comparable with the sclerotia of
Sclerotium rolfsii Sacc. than the sclerotia of Sclerotinia sclero-







Florida Agricultural Experiment Station


tiorum (Lib.) Massee. In the case of Corticium stevensii they
adhere to the host plant during unfavorable conditions and when
the host plant is dormant. They act as initials for the develop-
ment of mycelium and rhizomorphic strands at the beginning of
the season. Stevens (17) considered the sclerotia as hibernat-
ing structures which acted as initials and were usually present
near the terminal buds. Stevens & Hall (20) observed the scle-
rotia as being compact masses of hyphae which were of the same

























Fig. 105.-Corticium stevensii on: A, leaf; B, petiole, twig; C, nut of tung-
oil tree (Aleuroides fordii).

context throughout, having no epidermis or wall, measuring
3-4 mm. in length.
Basidia and Basidiospores: Noack (9) in describing the fun-
gus stated that no fruiting bodies were found. Eustace (5) ob-
served the basidia and stated that they were hyaline, smooth
and contained four sterigmata. The spores were 4-51/ x 21/2-
31/ t(, averaging 5 x 31,/2 /. Burt (3) observed basidia of the
fungus, stating that they were scattered over the surface of in-







Bulletin 186, Thread Blight


vaded leaves, that they produced four sterigmata and that the
basidia measured 7-8 x 11 p. He also described the basidio-
spores as being hyaline, flat or concave on one side, 3-4 x 11 1%
in size. The basidia are between 20-30 t in length and average
6-10 p in width. They develop from the cells'in the mycelium
which overgrows the epidermis. Their development is almost
without exception at right angles to the mycelial strands. The
contents of the cells in the mycelium are more or less granular,
except of those cells which have produced basidia, and in these
instances the cell contents are aggregated along the walls and
the central area is occupied by one or more large, conspicuous
vacuoles. The sterigmata are inconspicuous, produced four in
number at the end of the basidium and are wedge-shaped, being
pointed at the upper end.
More than one basidiospore has not been observed at a single
time on any basidium. The spores are sub-globose to oval in
shape, about 6 p in length and 21/2-3 p in width.

PHYSIOLOGY

Artificial Culture: The fungus has been grown on an artifi-
cial medium in pure culture for more than two years and during
this time has produced growth very characteristic of Rhizoc-
tonia species. The growth is uniform and rapid, covering ordi-
nary petri dishes on potato dextrose agar in about three days.
The mycelium is at first a dirty white color, gradually chang-
ing to brown. As the culture ages a more or less matting of
the mycelium takes place. Numerous, scattered, loose aggre-
gates of hyphae form into sclerotia similar in texture to those
found on the host plant, but more irregular in size and shape.
No basidia have ever been found in artificial cultures, al-
though the sclerotia form in abundance. Two percent potato
dextrose agar is more favorable for the development of the fun-
gus than any of the dozen other media tried.

PATHOGENICITY

The fungus was isolated and grown in pure culture from
tung-oil (Fig. 106) and pear trees. Sclerotia were removed
from the twigs and, after being disinfected in a solution of
1:1000 corrosive sublimate and washed in sterile distilled water,







Bulletin 186, Thread Blight


vaded leaves, that they produced four sterigmata and that the
basidia measured 7-8 x 11 p. He also described the basidio-
spores as being hyaline, flat or concave on one side, 3-4 x 11 1%
in size. The basidia are between 20-30 t in length and average
6-10 p in width. They develop from the cells'in the mycelium
which overgrows the epidermis. Their development is almost
without exception at right angles to the mycelial strands. The
contents of the cells in the mycelium are more or less granular,
except of those cells which have produced basidia, and in these
instances the cell contents are aggregated along the walls and
the central area is occupied by one or more large, conspicuous
vacuoles. The sterigmata are inconspicuous, produced four in
number at the end of the basidium and are wedge-shaped, being
pointed at the upper end.
More than one basidiospore has not been observed at a single
time on any basidium. The spores are sub-globose to oval in
shape, about 6 p in length and 21/2-3 p in width.

PHYSIOLOGY

Artificial Culture: The fungus has been grown on an artifi-
cial medium in pure culture for more than two years and during
this time has produced growth very characteristic of Rhizoc-
tonia species. The growth is uniform and rapid, covering ordi-
nary petri dishes on potato dextrose agar in about three days.
The mycelium is at first a dirty white color, gradually chang-
ing to brown. As the culture ages a more or less matting of
the mycelium takes place. Numerous, scattered, loose aggre-
gates of hyphae form into sclerotia similar in texture to those
found on the host plant, but more irregular in size and shape.
No basidia have ever been found in artificial cultures, al-
though the sclerotia form in abundance. Two percent potato
dextrose agar is more favorable for the development of the fun-
gus than any of the dozen other media tried.

PATHOGENICITY

The fungus was isolated and grown in pure culture from
tung-oil (Fig. 106) and pear trees. Sclerotia were removed
from the twigs and, after being disinfected in a solution of
1:1000 corrosive sublimate and washed in sterile distilled water,







Florida Agricultural Experiment Station


were placed on poured potato agar plates. Mycelia strands
developed in abundance from the sclerotia after three days.
This fungus in pure culture was used in inoculation of the hosts
from which it was isolated and the disease was reproduced in
characteristic form after a period of six weeks. The organism
develops slowly at first; later it spreads rapidly.
Eustace (5), working with the fungus, inoculated 34 varieties
of apples and five varieties of pears by placing the fungus on
wounds, and in every case produced the disease. On unwounded
fruits of these varieties he was unable to reproduce the disease.
Noack (9) attempted some inoculation experiments on quince
but failed to reproduce the disease, probably, he thought, be-
cause of the lack of moisture.
Portions of the diseased material were cut from infected pear
trees and placed on the foliage and new growth of different
hosts. The disease was
transferred from dis-
eased pear material to
healthy pear trees, from
pear to soapberry, from
pear to tung-oil, from
pear to plum and from
pear to pistache. These
inoculations were made
July 6, 1926 during the
rainy season and in all
cases the disease was
readily produced on the
new host in less than 30
days.
The fungus is com-
paratively difficult to be
Fig. 106.-Fungus on grapefruit (Citrus brought to vigorous
grandis). brought to vigorous
growth after it has once
become dormant following the rainy season. Inoculations made
October 4, 1926 had not reproduced the disease by March 1,
1927, although the mycelium was growing on leaves of the in-
oculated plant. Other inoculation experiments are being con-
ducted at the present time in an endeavor to determine the
host range of this fungus.







Bulletin 186, Thread Blight


THE CAUSAL ORGANISM IN RELATION TO THE
PRODUCTION OF THE DISEASE

SEASONAL DEVELOPMENT

According to the seasons, Florida is considerably in advance
of other portions of the United States. Consequently the devel-
opment of the disease will be described according to month
rather than the season.
Smith & Stevens (15) observed that the fungus usually cov-
ered the new growth on infected pear trees by mid-summer.
In Florida the fungus remains dormant until about the first of
May. At this time trees have come to full foliage development
and new growth has been produced several inches in length.
The first growth of the fungus is from around the sclerotia.
Numerous fine mycelial strands develop. All of the sclerotia
on the past season's growth begin to show this development at
the same time, growth being the same from those formed near
the terminal buds and those formed 12 to 20 inches below the
buds. The first growth is quite uniform around each sclero-
tium. The strands which tend to grow up the twigs appear to
have more vitality than those that grow in other directions. In
approximately 6 to 10 weeks the fungus has involved the cur-
rent season's growth of the host plant, killing the foliage (Fig.
105) and in many instances forcing the twigs into premature
dormancy.
At the time the leaves of a pear tree show the disease it ap-
pears that the plant has been attacked by pear blight rather
than thread blight. The leaves turn black and adhere to the
twigs.
Trees have been more than 50 percent defoliated by mid-
summer in Florida by this disease and affected parts have been
forced into dormancy at this time. The fungus continues to
develop as long as the host plant remains in a growing condi-
tion. When a diseased tree goes into dormancy the sclerotia
are in characteristic numbers at the tips of the twigs, their
number diminishes in direct proportion to the distance back
from the terminal bud. In this condition the fungus remains
dormant over unfavorable periods. It is in a viable condition
and most ideal position to resume its destructiveness at the be-
ginning of the following season.







Florida Agricultural Experiment Station


SOURCE OF INOCULUM

The fungus survives the winter in the form of sclerotia
which adhere to the bark of the branches and twigs. During
the growing season they act as centers from which the mycelium
develops and overgrows the new twig growth, petioles and leaf
blades. In Florida they remain dormant from November to
early May. In the spring the fungus grows rapidly from these
centers, almost completely overgrowing the foliage by mid-
summer. Some sclerotia are formed on the twigs during this
time of rapid advancement but the greater majority of them
are formed after mid-summer.
Basidia and basidiospores have been found on the leaves that
have been overrun by the mycelium but these fruiting struc-
tures are exceedingly scarce. The spread of the disease in Flor-
ida can be accounted for by spore dissemination, the scattering
of leaves from diseased twigs, the petioles of which are covered
with viable sclerotia, the possibility of rhizomorphic strands
and sclerotia adhering to the feet of insects, birds and animals
and by the scattering of twigs and branches pruned or broken
by cultivators and caretakers.
Infection can take place at almost any time the host plant is
in a growing condition. The more succulent the host plant, ap-
parently, the more readily it is infected. Infection depends
much upon the contact of diseased material to growing parts.
(Fig. 106). The rhizomorphic strands have been observed
crossing from infected leaf blades to the cortex of year-old wood
and vice versa, implying that these strands have considerable
potentiality.
Smith & Stevens (15) state that a tree once infected is al-
ways infected and that from the point of infection toward the
new growth the fungus makes a clean sweep. This inference
is true under Florida conditions. It has not been observed to
have killed its host plant, although pear trees which were long
infected and observed for five years were slowly declining. The
fungus grows up the twig to the petioles where some strands
branch off and grow out on the petioles to the leaf blade where
they divide and sub-divide into a fan-like advancing margin
almost invisible in their fineness. In this way they spread
over the lower surface of the leaves, completely parasitizing
them and rapidly killing them.







Bulletin 186, Thread Blight


LONGEVITY

As previously stated, a tree once infected is apparently al-
ways infected. This is true in that the fungus is continually
advancing. The fungus remained viable, however, at the point
of original attack in the vicinity of Gainesville for about three
years. The fun-
gus has been
found virulent on r
branches that
have been in-
fected three
years. Traces of
infection on
wood older than L.


this have been
noted but in no
case were the
sclerotia viable.
The migratory
mycelium in
these cases and
most of the scle-
rotia were al-
most completely
disin tegrat-
ed. The fungus,
however, remains
exceedingly viru-
lent over a sin-
gle year. Each
year this viabil-
it y apparently
declines, probab-
ly because the
virulence of the
sclerotia is re-
duced by the
production each
season of the mi-
gratory strands.


Fig. 107.-Control by use of Bordeaux mixture. Old
growth heavily infected, new growth free of dis-
ease.







Florida Agricultural Experiment Station


OVERWINTERING

The fungus hibernates from one season to the next as sclero-
tia that are formed on the twigs and branches. Occasionally
sclerotia are formed on the petioles of the leaves but in this
instance they are less important as sources of inoculum, since
almost all of the hosts reported as attacked by this fungus in
Florida are deciduous, causing these sclerotia to fall to the
ground. New growth takes place from all sclerotia located on
the past season's growth, often three or four feet from the ter-
minal bud. The fungus becomes dormant when the leaves fall
and remains so until late spring, usually several weeks after
new growth starts.

CONTROL

Since this fungus has been found on mostly woody plants of
a perennial nature, rotation is out of the question. Sanitation
is not important as a control measure since the fallen leaves are
not the principal source of inoculum in the spring. Consequent-
ly fungicides were employed to control the spread of this dis-
ease. Most writers who have observed this disease recommend
Bordeaux mixture.
In Florida the combination of spraying and pruning has given
control of this disease. The spraying* experiments were con-
ducted in 1924 in which a half dozen badly diseased pear trees
were sprayed with 4-4-50 Bordeaux mixture. Six applications
were made at intervals of about two weeks upon these trees
with the exception of one tree which was left as a check. No
spraying was done during the following season in order to de-
termine the percent of control. The check tree showed the dis-
ease which developed over considerable portions, causing ap-
proximately 50 percent defoliation. The sprayed trees for the
most part were free of the disease. The sclerotia which had
formed during the past season still adhered to the sprayed
twigs but the mycelial growth from these did not appear.
(Fig. 107.) There were two or three twigs on each of the
sprayed trees that had apparently been missed during the spray-
ing operations of the previous season which showed develop-
ment of the disease and the killing of enough foliage to be de-

*Mr. Harold Mowry of the Horticultural Department cooperated in
carrying on the control experiments.







Florida Agricultural Experiment Station


OVERWINTERING

The fungus hibernates from one season to the next as sclero-
tia that are formed on the twigs and branches. Occasionally
sclerotia are formed on the petioles of the leaves but in this
instance they are less important as sources of inoculum, since
almost all of the hosts reported as attacked by this fungus in
Florida are deciduous, causing these sclerotia to fall to the
ground. New growth takes place from all sclerotia located on
the past season's growth, often three or four feet from the ter-
minal bud. The fungus becomes dormant when the leaves fall
and remains so until late spring, usually several weeks after
new growth starts.

CONTROL

Since this fungus has been found on mostly woody plants of
a perennial nature, rotation is out of the question. Sanitation
is not important as a control measure since the fallen leaves are
not the principal source of inoculum in the spring. Consequent-
ly fungicides were employed to control the spread of this dis-
ease. Most writers who have observed this disease recommend
Bordeaux mixture.
In Florida the combination of spraying and pruning has given
control of this disease. The spraying* experiments were con-
ducted in 1924 in which a half dozen badly diseased pear trees
were sprayed with 4-4-50 Bordeaux mixture. Six applications
were made at intervals of about two weeks upon these trees
with the exception of one tree which was left as a check. No
spraying was done during the following season in order to de-
termine the percent of control. The check tree showed the dis-
ease which developed over considerable portions, causing ap-
proximately 50 percent defoliation. The sprayed trees for the
most part were free of the disease. The sclerotia which had
formed during the past season still adhered to the sprayed
twigs but the mycelial growth from these did not appear.
(Fig. 107.) There were two or three twigs on each of the
sprayed trees that had apparently been missed during the spray-
ing operations of the previous season which showed develop-
ment of the disease and the killing of enough foliage to be de-

*Mr. Harold Mowry of the Horticultural Department cooperated in
carrying on the control experiments.








Bulletin 186, Thread Blight


Fig. 108.-Pear trees (Pyrus betulaefolia) showing, A. Con-
trol of disease by Bordeaux mixture spray. B. Check tree
defoliated by disease unsprayed.







Florida Agricultural Experiment Station


tected. These diseased twigs were pruned out, giving 100 per-
cent control of the disease.
During the current season several pomegranate trees showed
considerable loss of foliage ?from the development of this dis-
ease. In this condition these trees were sprayed with 4-4-50
Bordeaux mixture. The fungicide immediately stopped the de-
velophment of the disease and in about three weeks new growth
developed from buds. which were completely surrounded by the
fungus.
Sanitary methods in which fallen leaves were destroyed made
little difference in the prevalence of the disease.

CONCLUSIONS

1. Thread blight caused by Corticium stevensii Burt is a
common, though not epidemically destructive disease in Florida.
2. New hosts herein reported for this disease are: Virginia
creeper, plum, pistache, soapberry, rose, pomegranate, persim-
mon, jujube, Chinaberry, morning-glory, mu-oil tree and tung-
oil tree.
3. 'The fungus sometimes causes as much as 50 percent de-
foliation.
4. Characteristic symptoms of the diseases are a matting
together of killed leaves by fungous strands and the presence
of superficial sclerotia.
5. The fungus in pure culture grows well on potato dextrose
agar.
6. The fungus over-winters in the form. of sclerotia which
act as centers of inoculum during the succeeding season.
7. The disease is controlled by the application of 4-4-50
Bordeaux mixture, accompanied by careful pruning.








Bulletin 186, Thread Blight 161

LITERATURE CITED
1. BURGER, O. F.
Reports of the Plant Pathologist, Fla. Agr. Exp. Sta. Ann. Rep.
1922, '23, '24, '25.

2. BURT, E. A.
The Telephoraceae of North America. Ann. Mo. Bot. Garden 1:193,
1914.

3.
Corticium causing Pellicularia disease of the coffee plant, hypoch-
nose of pomaceous fruits and Rhizoctonia disease. Ann. Mo. Bot.
Garden 5:119, 1918.

4. COOK, M. T.
The diseases of tropical plants, p. 174, Macmillan & Co., 1913.

5. EUSTACE, H. J.
Two decays of stored apples. N. Y. Agr. Exp. Sta. (Geneva) Bul.
235: 124-129. 1903.

6. FAWCETT, G. L.
Pellicularia koleroga on coffee in Porto Rico. Jour. Agr. Res. 2:
231. 1914.

7.
Fungus diseases of coffee in Porto Rico. Porto Rico Agric. Exp.
Sta. Bul. 17. 1915.

8. HESLER, L. R. & WHETZEL, H. H.
Manual of fruit diseases, pp. 135-137. Macmillan & Co. 1920.

9. NOACK, F.
Cogumelas, parasitas das plants de pomar horta e jardin. Boletin
do Inst. Agron. Sao Paulo, Brazil. Vol. 9: 80-81. 1898.

10. NOWELL, WM.
Diseases of crop plants in the lesser Antilles, pp. 149-151. West In-
dian Comm., 14 Trinity Sq., London.

11. PELTIER, G. L.
Parasitic Rhizoctonias in America. Ill. Exp. Sta. Bul. 189: 290.
1916.

12. QUAINTANCE, A. L.
Disease of apples and pears. 13th Ann. Rept. Ga. Agr. Exp. Sta.,
p. 359. 1901.

13. SACCARDO, P. A.
Syllogue Fungorum 16: 197.

14. SHELDON, J. L.
Rpt. W. Va. Expt. Sta., p. 31. 1906.







162 Florida Agricultural Experiment Station

15. SMITH, R. I. & STEVENS, F. L.
Insects and fungous diseases of apples and pears. Hypochnose.
N. Car. Agr. Exp. Sta. Bul. 206: 90-94, 1910.
16. STEVENS, F. L.
Plant disease fungi. Macmillan Co., N. Y., 1925.

17.
The fungi which cause plant disease. Macmillan Co., 1919.
18. & HALL, J. G.
Disease of economic plants, pp. 47, 69, 73, Macmillan Co., 1921.

19.
Two interesting apple fungi. Sci. 26: 724. 1907.
20.
Hypochnus of pomaceous fruits. Rpt. N. Car. Agr. Exp. Sta. 3:
76-85, 1909.
21.
Hypochnose of pomaceous fruits. Ann. Myc. 7: 49. 1909.




University of Florida Home Page
© 2004 - 2010 University of Florida George A. Smathers Libraries.
All rights reserved.

Acceptable Use, Copyright, and Disclaimer Statement
Last updated October 10, 2010 - - mvs