• TABLE OF CONTENTS
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 Historic note
 The cause
 Avocado
 Mango
 Control
 Literature cited














Group Title: Homestead AREC research report - University of Florida, Agricultural Research and Education Center ; SB79-6
Title: Mango and Avocado verticllium wilt
CITATION THUMBNAILS PAGE IMAGE ZOOMABLE
Full Citation
STANDARD VIEW MARC VIEW
Permanent Link: http://ufdc.ufl.edu/UF00067820/00001
 Material Information
Title: Mango and Avocado verticllium wilt
Series Title: Homestead AREC research report
Physical Description: 4 leaves : ; 28 cm.
Language: English
Creator: Marlatt, Robert B ( Robert Bruce ), 1920-
Agricultural Research and Education Center, Homestead
Publisher: University of Florida, Agricultural Research and Education Center
Place of Publication: Homestead Fla
Publication Date: 1979
 Subjects
Subject: Mango -- Diseases and pests -- Florida   ( lcsh )
Avocado -- Diseases and pests -- Florida   ( lcsh )
Verticillium wilt diseases -- Florida   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
non-fiction   ( marcgt )
 Notes
Statement of Responsibility: R.B Marlatt
General Note: "October 11, 1979."
 Record Information
Bibliographic ID: UF00067820
Volume ID: VID00001
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: oclc - 72481341

Table of Contents
    Historic note
        Copyright
    The cause
        Page 1
    Avocado
        Page 1
    Mango
        Page 2
    Control
        Page 2
    Literature cited
        Page 3
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






l/o) Homestead AREC Research Report SB79-6
C Mango and Avoi


October 11, 1979


cado Verticillium Wilt


qbV

7q


The causal fungus is a facultative parasite which normally derives all of its nour-
ishment from its host; however, it competes successfully with other-organisms when
living in soil on plant debris. One stage of its life cycle consists of micro-
sclerotia, which are minute, hard black bodies that are extremely resistant to un-
favorable environment. Although very small, each microsclerotium contains suffi-
cient stored food to germinate repeatedly during temporary conditions favoring the
fungus' vegetative growth; hence Verticillium can survive in soil for at least 15
years even in the absence of plant hosts (6). The pathogen can be transported from
one area to another as microsclerotia in soil or plant parts or can be airborne in
* the form of conidia, delicate spores which must infect a plant soon after being re-
leased. Conidia can germinate on and infect roots or rarely may infect foliage.

AVOCADO
Verticillium wilt of avocado (Persea americana Mill.) was first described in
California in 1949 (7) and had previously been considered a result of overly wet
soil rather than a fungus disease. Trees 2 to at least 20 years old are suscepti-
ble; some express symptoms and temporarily recover year after year while others may
be diseased only one year followed by apparently permanent recovery. Typical ex-
ternal symptoms include wilting of leaves which quickly turn brown on only some
branches, often on just one side of the tree. The disease is easily diagnosed fol-
lowing removal of some bark with a knife; the outer layer of sapwood is discolored
by brownish streaks extonding from large dead or dying branches to small twigs (7).

In California, Guatemalan rootstocks of av-ocado are generally more susceptible than
those of Mexican parentage (8); however, no comparisons of susceptibility have been
made in Florida.

The disease appears in late fall and winter when soil tempcraturos are low enough to
favor infection. The fungus producco most abhndaib nt-mi.roscclrotia at approximately
50 to 720F (10-22 C). When soil becomes warmer again new infections cease and
branch die-back stops as new wood forms over infected tissue. Numerous buds and
shoots appear on the trunk below dead wood as trees recover.

* Verticillium wilt of avocado was first identified in Florida in 1968 and was re-
ported the following year (3). Approximately 24 diseased trees were found scattered
throughout an 11-acre grove near Homestead which had been planted with 'Simmonds'
and 'Ruehle' cultivars in 1966. Both cultivars were equally affected.


S*R. B. Marlatt I .--
Plant Pathologist H ME L RAD
University of Florida, IFAS
Agricultural Research and Education Center 1979
Homestead, Florida 33031

THE CAUSE o.Un Fil.orida
Verticillium is a soil-borne fungus parasitic on economic plants aa&.weeds; it was
first found in potatoes in Germany in 1870. The fungus has most likely existed
since prehistoric times in various parts of the world, particularly in alkaline
soils. The species causing wilting of avocados and mangos is Verticillium albo-
atrum Reinke & Berth., the cause of disease of over 300 different plants. Many
plant species which are not considered susceptible to verticillium wilt may, never-
theless, have their roots colonized by the fungus without apparent damage.






l/o) Homestead AREC Research Report SB79-6
C Mango and Avoi


October 11, 1979


cado Verticillium Wilt


qbV

7q


The causal fungus is a facultative parasite which normally derives all of its nour-
ishment from its host; however, it competes successfully with other-organisms when
living in soil on plant debris. One stage of its life cycle consists of micro-
sclerotia, which are minute, hard black bodies that are extremely resistant to un-
favorable environment. Although very small, each microsclerotium contains suffi-
cient stored food to germinate repeatedly during temporary conditions favoring the
fungus' vegetative growth; hence Verticillium can survive in soil for at least 15
years even in the absence of plant hosts (6). The pathogen can be transported from
one area to another as microsclerotia in soil or plant parts or can be airborne in
* the form of conidia, delicate spores which must infect a plant soon after being re-
leased. Conidia can germinate on and infect roots or rarely may infect foliage.

AVOCADO
Verticillium wilt of avocado (Persea americana Mill.) was first described in
California in 1949 (7) and had previously been considered a result of overly wet
soil rather than a fungus disease. Trees 2 to at least 20 years old are suscepti-
ble; some express symptoms and temporarily recover year after year while others may
be diseased only one year followed by apparently permanent recovery. Typical ex-
ternal symptoms include wilting of leaves which quickly turn brown on only some
branches, often on just one side of the tree. The disease is easily diagnosed fol-
lowing removal of some bark with a knife; the outer layer of sapwood is discolored
by brownish streaks extonding from large dead or dying branches to small twigs (7).

In California, Guatemalan rootstocks of av-ocado are generally more susceptible than
those of Mexican parentage (8); however, no comparisons of susceptibility have been
made in Florida.

The disease appears in late fall and winter when soil tempcraturos are low enough to
favor infection. The fungus producco most abhndaib nt-mi.roscclrotia at approximately
50 to 720F (10-22 C). When soil becomes warmer again new infections cease and
branch die-back stops as new wood forms over infected tissue. Numerous buds and
shoots appear on the trunk below dead wood as trees recover.

* Verticillium wilt of avocado was first identified in Florida in 1968 and was re-
ported the following year (3). Approximately 24 diseased trees were found scattered
throughout an 11-acre grove near Homestead which had been planted with 'Simmonds'
and 'Ruehle' cultivars in 1966. Both cultivars were equally affected.


S*R. B. Marlatt I .--
Plant Pathologist H ME L RAD
University of Florida, IFAS
Agricultural Research and Education Center 1979
Homestead, Florida 33031

THE CAUSE o.Un Fil.orida
Verticillium is a soil-borne fungus parasitic on economic plants aa&.weeds; it was
first found in potatoes in Germany in 1870. The fungus has most likely existed
since prehistoric times in various parts of the world, particularly in alkaline
soils. The species causing wilting of avocados and mangos is Verticillium albo-
atrum Reinke & Berth., the cause of disease of over 300 different plants. Many
plant species which are not considered susceptible to verticillium wilt may, never-
theless, have their roots colonized by the fungus without apparent damage.






-2-

Verticillium wilt symptoms seen in this grove were virtually the same as those
* previously described in California. Foliage on scattered trees died and branches
died back from their tips during October through December; green twigs turned black
and sapwood contained brown streaks. Such symptoms had occasionally been attributed
to lightning damage in years past. None of the diseased trees died but most lost
25 to 75 percent of their foliage. In January the disease abated and the trees re-
covered.

Most of the land in this grove had been cleared of native pine and palmetto in 1964
and tomatoes were grown during two winters prior to planting avocados. Verticilliur
wilt in Florida tomatoes was first reported in 1959 (1). They are very susceptible
to the disease and their widespread cultivation in southern Dade County has created
a large reservoir of fungus inoculum in local soils.

In late December the Dade County Fruit Crops Extension Agent, Seymour Goldweber,
submitted for diagnosis an avocado branch with dead leaves and blackened twigs
which had been obtained from the grove described above. Fragments of discolored
sapwood were cultured on several media and incubated at 22 C. Within one week
colonies of a Verticillium grew from all fragments. Samples from several colonies
were transferred to Talboy's medium (4) upon which the fungus formed numerous black,
gritty and fibrous microsclerotia, typical of Verticillium albo-atrum Reinke and
Berth.

To verify pathogenicity year-old avocado seedlings were inoculated with the Verti-
cillium isolate. A few weeks later the trees lost some wilted leaves and developed
discolored sapwood. Control plants which were not inoculated remained symptomless.
Pieces of the discolored wood yielded Verticillium when placed on culture medium,
S proving its pathogenicity.

MANGO

During the winter of 1969-70 young mango trees (Mangifera indica L.) were declining
and dying-back in scattered areas of a grove in southern Dade County; eventually
almost all trees in this grove developed symptoms which closely resembled verticil-
lium wilt in avocado and a few died. The mangos had also been planted in soil pre-
viously cropped to tomatoes. Surveys failed to reveal any cultivar resistance in
affected groves.

Laboratory studies of discolored mango wood revealed the presence of the same Verti-
cillium species that had been found in avocado. Pathogenicity tests with the
'Terpentine' mango seedlings proved that V. albo-atrum was causing the di!,easo. As
far as can be determined by a literature search, this is the first report of verti-
cillium wilt of mango.

CONTROL

Injection of iron chelate into soil under mangos has hastened recovery from verEb-
cillium wilt. Two ounces of Sequestrene 138 in 5 gallons of water per tree Was an
effective concentration (2).

Recommendations for control of verticillium wilt in avocado and mango are the.same.
After trees have fully recovered, dead wood should be pruned away and removed from
* the grove or burned because it contains microsclerotia of the fungus.

These fruits must not be planted in land that has previously been cropped to Verti-
cillium susceptible species such as tomatoes, potatoes, eggplants, peppers and the
many other hosts of the fungus. Growers occasionally interplant annual crops






-2-

Verticillium wilt symptoms seen in this grove were virtually the same as those
* previously described in California. Foliage on scattered trees died and branches
died back from their tips during October through December; green twigs turned black
and sapwood contained brown streaks. Such symptoms had occasionally been attributed
to lightning damage in years past. None of the diseased trees died but most lost
25 to 75 percent of their foliage. In January the disease abated and the trees re-
covered.

Most of the land in this grove had been cleared of native pine and palmetto in 1964
and tomatoes were grown during two winters prior to planting avocados. Verticilliur
wilt in Florida tomatoes was first reported in 1959 (1). They are very susceptible
to the disease and their widespread cultivation in southern Dade County has created
a large reservoir of fungus inoculum in local soils.

In late December the Dade County Fruit Crops Extension Agent, Seymour Goldweber,
submitted for diagnosis an avocado branch with dead leaves and blackened twigs
which had been obtained from the grove described above. Fragments of discolored
sapwood were cultured on several media and incubated at 22 C. Within one week
colonies of a Verticillium grew from all fragments. Samples from several colonies
were transferred to Talboy's medium (4) upon which the fungus formed numerous black,
gritty and fibrous microsclerotia, typical of Verticillium albo-atrum Reinke and
Berth.

To verify pathogenicity year-old avocado seedlings were inoculated with the Verti-
cillium isolate. A few weeks later the trees lost some wilted leaves and developed
discolored sapwood. Control plants which were not inoculated remained symptomless.
Pieces of the discolored wood yielded Verticillium when placed on culture medium,
S proving its pathogenicity.

MANGO

During the winter of 1969-70 young mango trees (Mangifera indica L.) were declining
and dying-back in scattered areas of a grove in southern Dade County; eventually
almost all trees in this grove developed symptoms which closely resembled verticil-
lium wilt in avocado and a few died. The mangos had also been planted in soil pre-
viously cropped to tomatoes. Surveys failed to reveal any cultivar resistance in
affected groves.

Laboratory studies of discolored mango wood revealed the presence of the same Verti-
cillium species that had been found in avocado. Pathogenicity tests with the
'Terpentine' mango seedlings proved that V. albo-atrum was causing the di!,easo. As
far as can be determined by a literature search, this is the first report of verti-
cillium wilt of mango.

CONTROL

Injection of iron chelate into soil under mangos has hastened recovery from verEb-
cillium wilt. Two ounces of Sequestrene 138 in 5 gallons of water per tree Was an
effective concentration (2).

Recommendations for control of verticillium wilt in avocado and mango are the.same.
After trees have fully recovered, dead wood should be pruned away and removed from
* the grove or burned because it contains microsclerotia of the fungus.

These fruits must not be planted in land that has previously been cropped to Verti-
cillium susceptible species such as tomatoes, potatoes, eggplants, peppers and the
many other hosts of the fungus. Growers occasionally interplant annual crops






-3-


between their rows of young trees until they are large enough to yield fruit. The
intercrop must not be susceptible to verticillium wilt. No satisfactory method has
yet been found for elimination of Verticillium from our limestone soils.

Since the fungus is systemic in sapwood it is not wise to obtain budwood from trees
in a grove that previously contained diseased trees.



Literature Cited

1. Conover, R. A. 1959. Verticillium wilt of tomato in Dade County, Florida.
Proc. Florida State Hort. Soc. 72:199-201.

2. Goldweber, Seymour. 1975. The use of a chelated iron to restore normal vigor
to verticillium wilt infected mango trees. Proc. Florida State Hort. Soc.
88:499-500.

3. Marlatt, R. B., and Seymour Goldweber. 1969. Verticillium wilt of avocado
(Persea americana) in Florida. Plant Disease Reptr. 53:583-584.

4. Marlatt, R. B., R. J. Knight and Seymour Goldweber. 1970. Verticillium wilt of
mango (Mangifera indica)'in Florida. Plant Disease Reptr. 54:569-571.

5. Talboys, P. W. 1960. A culture medium aiding the identification of Verticil-
lium albo-atrum and V. dahliae. Plant Path. 9:57-58.

6. Wilhelm, S. 1955. Longevity of the Verticillium wilt fungus in the laboratory
and field. Phytopathology 45:180-181.

7. Zentmeyer, G. A. 1949. Verticillium wilt of avocado. Phytopathology
39:677-682.

8. Zentmeyer, G. A., F. F. Halma and S. Wilhelm. 1955. Relative susceptibility
of Guatemalan and Mexican avocado rootstocks to Verticillium wilt.
Phytopathology 45:635-636.




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