Title Page
 Nature of the disease
 Summary of work at Leesburg...
 Description of the new melon
 General discussion

Group Title: Bulletin - University of Florida Agricultural Experiment Station ; 288
Title: wilt-resistant watermelon for Florida
Full Citation
Permanent Link: http://ufdc.ufl.edu/UF00027675/00001
 Material Information
Title: wilt-resistant watermelon for Florida
Series Title: Bulletin - University of Florida Agricultural Experiment Station ; 288
Physical Description: Book
Language: English
Creator: Walker, M. N.
Publisher: University of Florida Agricultural Experiment Station
Publication Date: 1936
 Record Information
Bibliographic ID: UF00027675
Volume ID: VID00001
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.

Table of Contents
    Title Page
        Page 1
        Page 2
        Page 3
    Nature of the disease
        Page 4
        Page 5
        Page 6
        Page 7
    Summary of work at Leesburg laboratory
        Page 8
        Page 9
    Description of the new melon
        Page 10
        Page 11
    General discussion
        Page 12
        Page 13
        Page 14
        Page 15
        Page 16
Full Text

January, 1936






Fig. 1.-General view of the 1935 experimental field, showing heavy stand
of the Leesburg variety on land that has produced six successive crops of
melons. (Photographed May 25.)

Bulletins will be sent free to Florida residents upon application to

Bulletin 288


John J. Tigert, M.A., LL.D., President of the
Wilmon Newell, D.Sc., Director
H. Harold Hume, M.S., Asst. Dir., Research
Harold Mowry, M.S.A., Asst. Dir., Adm.
J. Francis Cooper, M.S.A., Editor
Jefferson Thomas, Assistant Elitor
Clyde Beale. A.B.J., Assistant Editor
Ida Keeling Cresap, Librarian
Ruby Newhall, Administrative Manager
K. H. Graham, Business Manager
Rachel McQuarrie, Accountant


W. E. Stokes, M.S., Agronomist**
W. A. Leukel, Ph.D., Agronomist
G. E. Ritchey, M.S.A., Associate*
Fred H. Hull, Ph.D., Associate
W. A. Carver, Ph.D., Associate
John P. Camp, M.S., Assistant
A. L. Shealy, D.V.M., Animal Husbandman**
R. B. Becker, Ph.D., Dairy Husbandman
W. M. Neal, Ph.D., Asso. in An. Nutrition
D. A. Sanders, D.V.M., Veterinarian
M. W. Emmel, D.V.M., Asst. Veterinarian
N. R. Mehrhof, M.Agr., Poultry Husbandman
W. W. Henley, B.S.A., Asst. An. Husbandman
Bradford Knapp, Jr., M.S., Asst. An. Husb.
P. T. Dix Arnold, B.S.A., Assistant Dairy
L. L. Rusoff, M.S, Laboratory Assistant
Jeanette Shaw, M.S., Laboratory Technician
R. W. Ruprecht, Ph.D., Chemist**
R. M. Barnette, Ph.D., Chemist
C. E. Bell, Ph.D., Associate
R. B. French, Ph.D., Associate
H. W. Winsor, B.S.A., Assistant
C. V. Noble, Ph.D., Agricultural Economist*
Bruce McKinley, A.B., B.S.A., Associate
Zach Savage, M.S.A., Associate
A. H. Spurlock, M.S.A., Assistant
Ouida Davis Abbott, Ph.D., Specialist**
C. F. Ahmann, Ph.D., Physiologist
L. W. Gaddum, Ph.D., Biochemist
L. H. Rogers, M.A., Spectroscopic Analyst
J. R. Watson, A.M., Entomologist**
A. N. Tissot, Ph.D., Associate
H. E. Bratley, M.S.A., Assistant
A. F. Camp, Ph.D.. Horticulturist**
G. H. Blackmon, M.S.A., Horticulturist and
Associate Head of Department
A. L. Stahl, Ph.D., Associate
F. S. Jamison, Ph.D., Truck Horticulturist
R. J. Wilmot, M.S.A., Specialist, Fumigation
R. D. Dickey, B.S.A., Assistant Horticulturist
W. B. Tisdale, Ph.D., Plant Pathologist**
George F. Weber, Ph.D., Plant Pathologist
R. K. Voorhees, M.S., Assistant***
Erdman West, M.S., Mycologist
Lillian E. Arnold, M.S., Assistant Botanist
Stacy 0. Hawkins, M.A., Assistant Plant

Geo. H. Baldwin, Chairman, Jacksonville
A. H. Blanding, Bartow
A. H. Wagg, West Palm Beach
Oliver J. Semmes, Pensacola
Harry C. Duncan, Tavares
J. T. Diamond, Secretary, Tallahassee

L. O. Gratz, Ph.D., Plant Pathologist in
R. R. Kincaid, Ph.D., Asso. Plant Pathologist
J. D. Warner, M.S., Agronomist
Jesse Reeves, Farm Superintendent
A. F. Camp, Ph.D., Horticulturist in Charge
John H. Jefferies, Superintendent
W. A. Kuntz, A.M., Assoc. Plant Pathologist
B. R. Fudge, Ph.D., Associate Chemist
W. L. Thompson, B.S., Asst. Entomologist
A. Daane, Ph.D., Agronomist in Charge
R. N. Lobdell, M.S., Entomologist
F. D. Stevens, B.S., Sugarcane Agronomist
Thomas Bregger, Ph.D., Sugarcane Physiologist
G. R. Townsend, Ph.D., Assistant Plant
J. R. Neller, Ph.D., Biochemist
R. W. Kidder, B.S., Assistant Animal
Ross E. Robertson, B.S., Assistant Chemist
B. S. Clayton, B.S.C.E., Drainage Engineer
H. S. Wolfe, Ph.D., Horticulturist in Charge
W. M. Fifield, M.S., Asst. Horticulturist
Geo. D. Ruehle, Ph.D., Associate Plant
W. F. Ward, M.S.A., Asst. An. Husbandman
in Charge*

M. N. Walker, Ph.D., Plant Pathologist in
W. B. Shippy, Ph.D,. Asso. Plant Pathologist
K. W. Loucks, M.S., Asst. Plant Pathologist
J, W. Wilson, Ph.D., Associate Entomologist
Plant City
A. N. Brooks, Ph.D., Plant Pathologist
A. S. Rhoads, Ph.D., Plant Pathologist
A. H. Eddins, Ph.D., Plant Pathologist
G. B. Fairchild, M.S., Asst. Entomologist***
Davi G. Kelbert, Asst. Plant Pathologist
C. C. Goff, M.S., Assistant Entomologist
E. R. Purvis, Ph.D., Assistant Chemist,
Celery Investigations
E. S. Ellison, Ph.D., Meteorologist*
B. H. Moore, A.B., Asst. Meteorologist*
W. O. Johnson, B.A., Asst. Meteorologist*
R. T. Sherouse, Asst. Meteorologist*
M. L. Blanc, Asst. Meteorologist*

*In cooperation with U.S.D.A.
** Head of Department.
*** On leave.




Fusarium wilt of watermelons has been known in the South-
ern states for more than 40 years, and at present it occurs
in practically all sections of the United States where water-
melons are grown commercially. Under conditions of heavy
soil infestation the disease may cause complete loss of the crop
and ordinary conditions of soil infestation are capable of caus-
ing from 20 to 50 percent loss of stand. In Florida the wilt
disease is widespread and on this account growers of large acre-
ages use virgin land each year to avoid ravages of the disease.
Since it is probable that a comparatively small percentage of
the soil becomes infested the first year, growers of smaller acre-
ages in some sections of the state replant the same land after
a period of five to seven years.
Clearing and fencing new land each year involves heavy ex-
pense and, as the fields become located farther from the high-
ways and railroads, there is also an increase in the costs of
transporting equipment, labor and the crop. In addition to
these factors of increased costs of production, which are di-
rectly attributable to the wilt disease, there is the further eco-
nomic loss occasioned by the abandonment of fields that cannot
be planted profitably to some other crop. Because of the condi-
tion of agriculture at the present time, the large acreage of
land cleared annually for watermelons in the Leesburg area
cannot be used to advantage for other crops, with the result
that thousands of acres once used for this crop have been aban-
doned to the growth of scrub oak, which in a few years will
make it very expensive to re-clear this land for any purpose.
The continuous use of new land in this area has practically de-
pleted the supply and, unless a marketable, resistant variety
is grown, the industry in this particular area must decline.
Recognizing these facts, certain growers foresaw that unless
a satisfactory control of the wilt disease was developed Lake
County ultimately would lose a valuable industry. Consequently,
these men were instrumental in securing an appropriation by
the Legislature of 1929, which provided funds for a study of

Florida Agricultural Experiment Station

the wilt problem. Work was started in the spring of 1930 and
has been carried on continuously since that time at Leesburg.
The purpose of this paper is to describe a new variety of wilt-
resistant melon that has been developed and to review briefly
the work connected with its development.
Since many growers apparently do not understand the nature
and cause of the wilt disease and often confuse it with anthrac-
nose and other diseases of the watermelon plant, a brief review
of the principal characteristics of wilt follows.

The fungus causing wilt was first recognized and described
more than 40 years ago as Fusarium niveum E. F. S. It be-
longs to a group of fungi which cause wilt diseases in such
crops as asters, cabbage, cotton, cowpeas, flax and tomatoes.
This fungus, like all other fungi, is a plant and as such it grows
and reproduces in a manner somewhat similar to that of flower-
ing plants. Its reproductive elements, which function like the
seeds of higher plants, are known as spores. They are so
small that they can be seen only with the aid of considerable

Fig. 2.-Culture plates showing wilt fungus growing out of pieces of
diseased watermelon stem.

A Wilt-Resistant Watermelon for Florida

magnification. These spores germinate and give rise to new
vegetative plants of the fungus. This fungus (and other mem-
bers of the group), however, has no chlorophyl, the green
coloring matter which enables the higher plants to elaborate
their own food out of materials obtained from the soil and air.
Consequently, its food has to be obtained either directly or in-
directly from the higher plants. Although the wilt fungus can
live an indefinite number of years on decaying plant material
in the soil, it is capable of attacking living watermelon plants;
that is, it is a parasite. (Figure 2 shows the fungus growing
out of sections of a diseased watermelon stem.) In Iowa it
has been found that the organism is capable of surviving in
the soil for 17 years after the cultivation of melons on the land
had been discontinued. Consequently, it is necessary to develop
other means of attacking the disease than by attempting to
starve it out by rotation of crops.
The wilt fungus may be introduced into new fields in a
number of ways. Apparently, a small number of the seeds of
melons from diseased vines carry the fungus and, when planted,
such infected seed will introduce the disease into clean soil.
More common and general means by which new areas may be-
come infested are the transportation of soil and plant material
from infested fields by water, the transportation of the fungus
in soil carried on cultivating implements and on the feet of
men and other animals. It is not unusual to find wilt first

Fig. 3.-Young watermelon plants in pots, showing damping-off form
of the wilt disease.

Florida Agricultural Experiment Station

appearing in new fields around water holes and other places
where cattle have congregated after having had the range of
neighboring infested fields.
Wilt may attack watermelon plants in any stage of their
development. Seedlings may be killed before they appear above
ground. Also, after appearing above ground, they are often
killed by a damping-off form of the disease, as illustrated in
Fig. 3. Growers generally are not familiar with these forms
of the disease, as losses of individual plants usually are not
noticed because of the large number of plants in a hill. How-
ever, after the plants
have been thinned to
a stand and have
Grown larger, af-
.: fected plants are
-r : more conspicuous
S., and exhibit distinct
Sw..ilt symptoms (Fig.
4). In commercial
Fields where the in-
festation usually is
.. ~ light, destruction
S" does not occur to
.. ..*r ..* ,.A any great extent
.rfs! *.: often until the vines
i*f .* '' .. are well-grown, and
*.: .. at this stage the ef-
fects of the disease
Fig. 4.-Watermelon plants in the field,
showing typical wilt symptoms. are very conspicuous
and disheartening.
Wilted plants may revive somewhat overnight, but the recovery
is only temporary and within a few days the plant is dead.
Vegetative growth of the fungus extends through the vascu-
lar system of affected plants and serves to impede the normal
passage of water to the leaves by actual plugging of the vessels
and by weakening the water-carrying system by direct attacks
on the walls by the fungus itself or possibly its toxic waste
products. This destruction of the vascular tissue is apparent
as brown streaks in longitudinal sections of diseased stems
(Fig. 5) and as brown or black centers of roots. This char-
acter of the disease has led to its being designated as "black-
root" by growers.

A Wilt-Resistant Watermelon for Florida

After the death of the plant, the fungus spreads rapidly
throughout the entire plant and produces masses of spores on
the surface. These are pale pink in color and are not especially
conspicuous. In this condition the fungus is easily disseminated
by wind, water, and
other agencies. Since
each of the countless
spores in the mass is
capable of initiating a
new infestation,the in- .
fested areas in fields
may increase greatly
in size from year to
year. Thus, it is haz-
ardous to plant a field I i
the second year with
the commercial varie- ," .
ties of melons. '.
In view of the fore- .
going facts, sprays or
dusts are valueless in
controlling the disease
and it is apparent that
the most feasible and
economic means of
combatting it is the
development of varie-
ties or strains of wa-
termelons that are re-
sistant to it. In the
area of Muscatine,
Iowa, where 90 per-
cent of the former
acreage was aban-
Fig. 5.-Longitudinal sections of lower por-
doned because of the tion of stems of wilted watermelon plants,
ravages of wilt, the showing browning of vascular tissue. Note in
stem at right that the discoloration is con-
use of wilt-resistant fined to one side.
varieties developed by
the Iowa Experiment Station has permitted a large part of
this acreage to be replanted. The varieties developed by the
Iowa Station, however, have not proved suitable for Florida

Florida Agricultural Experiment Station

conditions. Consequently, work has been in progress for the
last five years to develop a resistant melon that will meet the
market requirements for Florida-grown melons.

The fact that the watermelon was one of the crops in which
disease resistance was first observed and that workers in other
states have succeeded in developing watermelon strains resist-
ant to wilt encouraged the belief that it was possible to develop
wilt-resistant watermelons suitable for Florida conditions.
The first step in carrying out such a program was to test
under Florida conditions and in heavily wilt-infested soil as
many strains and varieties of watermelons as it was possible to
secure in the short time before the planting season of 1930.
In that year, 104 varieties and strains of watermelons, includ-
ing a few citron varieties, were tested for resistance.
The land selected for the experimental trials had been used
for growing watermelons four different seasons during the pre-
ceding 10 or 12 years, and in 1929 only one carload of melons
was harvested from the entire 40 acres. This low yield was
attributed to wilt, but it is possible that other diseases may have
been partly responsible. It was not possible to determine the
degree of wilt infestation in the soil before the first year's trials
or to build it up through the application of highly infective
material, such as cultures of the wilt fungus or with soil known
to be heavily infested with the fungus. As a result, it was found
that the field was not uniformly infested with the organism.
In all subsequent plantings, however, one or more applications
of a handful of heavily infested soil was added to each hill.
Furthermore, all of the plants dying from the disease were
chopped into the soil. The effects of this treatment may be
seen in Figure 6, which shows the general killing in a portion
of the field during 1931.
Fertilization and cultivation in the experimental field have
closely approximated the common practices in the Leesburg
area. The plants were counted frequently each season to check
on the amount of killing in the various strains. A final check
was made at the end of the season by cutting all surviving vines
and examining them for evidences of wilt infection.
Each year many strains were discarded because they showed
no conspicuous resistance to the disease or other especially de-
sirable characters. On this basis almost half of the 104 strains

A Wilt-Resistant Watermelon for Florida

were eliminated from further trial after the first season. Al-
though resistance has been the principal basis of selection, it
was necessary to pay attention to other desirable characters,
as toughness of rind and flesh quality. The most desirable
types of melons were saved from the strains showing the high-
est percentages of vigorous surviving plants, and occasionally
from conspicuously good plants occurring in strains that were
low in apparent resistance as a whole. The seeds of each
melon were maintained as a unit, and a card record made of
the various characters of the melons from which they were

Fig. 6.-View of portion of 1931 experimental field, showing very general
killing by wilt. The whole area was planted, but only a few strains showed
ability to withstand the disease. (Cf. Fig. 1.)

Since the number of lots of seeds saved each year was too
great to plant all of them in the field the following year, tests
were made in the greenhouse to determine their germination
and comparative resistance in the seedling stage. Those show-
ing up poorly in these tests were discarded. Since only a limited
number could be tested at one time and since it was found
that a single test was often not conclusive, it was not always
possible to test all of the lots of seeds in this manner. Other
eliminations were made on a basis of the melon field trial records
of the previous year. As the work progressed and the total
number of distinct strains decreased, it became increasingly
possible to pay more attention to type, quality, and rind char-
acter of the melons. Through these various means of elim-
inating the poorer strains, the number of original strains main-
tained at the present time has decreased to less than a dozen,

Florida Agricultural Experiment Station

and only a few of these are represented by seeds from more
than two or three individual melons. A few additional strains
have arisen through crossing among the various strains, and
some of these show considerable promise as a source of new
types that may prove more valuable than some of those secured
through straight selection. Considerable more time is neces-
sary to fix the various characters of the hybrids than is required
for selection of types from a more or less homogeneous variety.
During the course of the work a number of selections have
shown promise one year only to fail in subsequent trials. How-
ever, one selection from the 1931 field crop tested in 1932 was
outstanding for resistance and quality and its superiority has
been maintained since that time. Two types have been isolated
from this stock and sufficient seeds from one of them were
harvested in 1935 to plant several acres.
In the experimental trials of 1935, this melon showed up ex-
tremely well, as may be seen from Figure 1. The field shown
in the illustration has produced melons at least six times during
the past 14 years and large quantities of infective material were
added to the soil for the last two plantings to insure the ex-
posure of all plants to infection. Under these conditions the
various selections of this variety showed percentages of resist-
ance varying upward from 75 percent. Considering the fact
that there is probably not another field in the state with such a
uniformly high soil infestation, it appears that this melon should
prove valuable when grown in soil of lighter infestation.

This melon, which has been designated as the Leesburg, was
developed from the Kleckley Sweet variety, seeds of which were
obtained from a local seedstore, and possesses many characters
of that variety. Kleckley Sweet has long been considered to
have very high quality, but the tenderness of the rind has pre-
vented it from becoming an important commerical variety. Like
most commercial varieties of watermelons, the Kleckley Sweet
is not stable for all characters. Consequently, through continued
self-fertilization and selection, the Leesburg has been isolated.
It possesses certain characters not conspicuous in the Kleckley
Sweet and these are apparently fixed. The more important of
these characters, other than that of increased resistance to wilt,
are the increased toughness of the rind and its lighter color.
The melon is long and, although it is not quite so long as the

A Wilt-Resistant Watermelon for Florida

Fig. 7.-The Leesburg melon is of uniform shape and good shipping

original Kleckley, the ends are blockier. The surface of the
rind is smooth to faintly grooved and has a uniform medium
dark green color about midway between that of the Watson and
the Kleckley. It is thin to medium thick and is hard and tough,
comparing favorably in this respect with the Watson. The flesh
is a deep rose-pink color; has a fine, firm texture, extends well
into the ends and is clearly demarked from the rind. The seeds
are white. Exterior and interior views of a typical melon of
this variety are shown in Figures 7 and 8.

Fig. 8.-Good quality rose-pink flesh, plainly demarked from the rind,
is characteristic of the Leesburg melon.

Florida Agricultural Experiment Station

The sizes of the melons of the Leesburg variety have ranged
between 20 and 35 pounds, with most melons falling into the
25 to 30 pound class. In the experimental plots the melons
have not been "pruned" to one or two to the vine, as is com-
monly done in commercial fields. Consequently, it would appear
that uniformly larger sizes would result if "pruning" were
The character known as "white-heart" was not observed in
any of the melons produced in the 1935 experimental field.
Such strains as showed this defect in previous years were dis-
carded. Also, the Leesburg melon has remained comparatively
free from sunburn, and such injury as has been observed has
seldom resulted in rind softening. The keeping quality of the
melons appears very good, as some melons of this variety have
been kept for two weeks after maturity without evident deteri-
The chief objections to the Leesburg melon from the com-
mercial grower's viewpoint are the color of the flesh, which
is not so clear red as that of a good Watson, and the white
seeds, which are often considered to be an evidence of imma-
turity. Although these objections are sound in view of the
familiarity of the market with the Watson melon, it is believed
that the high quality of the Leesburg melon will offset them
when it has become better known, and will justify its general
planting, if tests in different parts of the State substantiate
the promise it has shown in the experimental plantings at Lees-
Some growers have expressed the idea that the introduction
of a satisfactory wilt-resistant melon would result in over-
production and thus ruin the market. Such a conception is
based on a misunderstanding of the problem as a whole.
In the first place, the reduction in the actual cost of production
per acre would only rarely amount to as much as 25 percent of
the current cost of growing an acre of watermelons, as the basic
costs of land rent, plowing, fertilization, cultivation, and insect
control will remain at approximately the current levels. Some
saving in clearing, fencing, and transportation should result,
but not enough to justify any decided increase in the acreage
devoted to the crop.
It is also probable that it will never prove advisable to attempt
to grow watermelons successively for a long period of years on

A Wilt-Resistant Watermelon for Florida

the same ground. Although this might be possible for a few
years, a number of factors would soon make economic pro-
duction difficult. Probably the most important of these factors
is root-knot, which may be equally as injurious as wilt after a
heavy infestation has been established, although it spreads less
rapidly. Another is the fact that repeated cultivation soon
removes from the soil the coarse material that serves as an
anchorage for the vines, thus increasing the chances for wind
injury. This has proved to be one of the greatest obstacles to
the repeated use of land in the experimental field. Repeated
cultivation also renders the soil more compact and, although
water retention is improved, the soil becomes colder than soil
containing more rough material in the form of roots and sticks.
Anthracnose control might also become more difficult, if crops of
watermelons were grown repeatedly on the same ground.
There are possibly other factors that should be considered,
but these points serve to illustrate the advisablility of rotating
the plantings of watermelons in the same manner that is con-
sidered good agricultural practice with other crops.
The chief value of this new wilt-resistant watermelon is
that it may be planted on wilt-infested soil. This will permit
the re-utilization of thousands of acres of land once used for
melons, but which are now considered unsafe. At the current
rate of planting in the Leesburg area, 3,000 to 4,000 acres a
year, it would take a long period of time to replant this great
area of land just once. The possibility that this land could
be used again would encourage ownership. A three- to five-year
rotation of this land appears entirely feasible without running
into serious difficulty with factors other than wilt.
From the preceding discussion it would appear evident that
the fear of injuring the industry through the use of a wilt-
resistant melon is not justified by the facts. On the other hand,
it must appear equally evident that unless such a melon is de-
veloped, the industry must certainly decline in those areas now
devoted primarily to the production of melons, leaving a vast
area of land to grow up to scrub oak. It is extremely unlikely
that some of this land will ever be used for watermelons again
because of the great cost of re-clearing it. However, most of
it could be used again, and such growth as there is on it now
would serve a useful purpose in furnishing anchorage for the

If information of a related character, additional to that
contained in the foregoing bulletin, would be of service,
you are cordially invited to write for it. List of bulletins
on the sundry phases of Florida agriculture also will be
furnished on request. Criticisms of the contents, and
suggestions for making these bulletins more helpful to
farmers and growers, will be received with appreciation.
Wilmon Newell, Director


Results of the investigations and research carried on at the Florida
Agricultural Experiment Stations are recited in the bulletins pub-
lished by this farm service agency. During the period of approaching
50 years that have elapsed since the work was begun, in 1887, more
than 288 of these bulletins have been issued. In print at the present
and available for distribution are some 95 of them, covering nearly
as many subjects vitally important to farmers, fruit growers, live-
stock raisers and truck crop producers. Any of these bulletins will
be furnished free on application, as will a list giving the titles, from
which selections may be made.
Application in practical agriculture of research findings, according
to methods of demonstrated merit, is described in bulletins which the
Florida Agricultural Extension Service publishes. Dealing primarily
with the "how" of doing the things that research endeavor has shown
to be feasible, these bulletins bring together science and practice.
Titles of the 25 issues now in stock will be supplied free on receipt
of request. Bulletins desired then may be obtained through the offices
of county farm and home demonstration agents or from the office of
Communications for either the Agricultural
Experiment Stations or the Agricultural Ex-
tension Service-both cooperative agencies of
state and federal governments-should be ad-
dressed to Gainesville, Florida, where they are
operated under the College of Agriculture in
the University of Florida, which also has a
division of resident teaching.

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