xt7j3t9d6j8j https://exploreuk.uky.edu/dips/xt7j3t9d6j8j/data/mets.xml   Kentucky Agricultural Experiment Station. 1953 journals 015 English Lexington : Agricultural Experiment Station, University of Kentucky Contact the Special Collections Research Center for information regarding rights and use of this collection. Kentucky Agricultural Experiment Station Progress report (Kentucky Agricultural Experiment Station) n.15 text Progress report (Kentucky Agricultural Experiment Station) n.15 1953 2014 true xt7j3t9d6j8j section xt7j3t9d6j8j Progress Report 15 October, 1953
EXPERIMENTAL PRODUCTION OF SEEDLESS WATERIVIELONS
j. Edward Klinker  
japanese seedless watermelons have produced fruits of outstanding quality
and flavor during three years of trial at the Horticultural Farm, Kentucky Agricul-
tural Experiment Station. A considerable number of the new and standard varieties
of regular watermelons have also been on trial during this period, but none consis-
tently produced fruits as high in quality as the japanese seedless melons.
This watermelon is a development of a number of japanese plant breeders.
An outstanding report of the investigations of these workers has been made by
Kihara (1951). So far as known, no other formal publications exist which describe
the breeding and culture of this melon except those of the japanese workers cited
by Kihara.
Triploid (seedless) watermelons, according to Kihara, are produced as
follows: “The common watermelon, Citrullus vulgare, Shrad, is diploid with somatic
(Zx) and gametic chromosome (x) numbers of 22 and ll, respectively, After tetra-
pldijs are at hand, triploids argproduced by crossing tetraploids with diploids
(x : Z2 x x : 11). Young diploid seedlings are treated with an aqueous solution of
c.olchicine‘(O.2. or 0.4 percent}, applied daily for four consecutive days. One drop
of colchicine solution, each day, on the growing point of young seedlings, constitutes
a successful schedule to produce tetraploids. Once tetraploids are obtained, they
breed true. Thereafter, triploids can be produced season after season by crossing
tetraploids (x : 22) with diploids (x : 11). However, only those crosses using the
diploid pol1in—ator and tetraploid seed parent produce viable triploid seed, the
reciprocal cross (x : ll x x ZZ) is unsuccessful." This explanation answers the
question “Where does one get seed to produce seedless watermelons? " In the opin»-
ion of the author, this breeding program is somewhat analogous to the production of
hybrid corn in that parental lines must be maintained.
At present there are two objections to the production of seedless water-
melons. First seed is expensive(from Z to 5 cents per seed) and, second, because
of a very hard seed coat, difficulty in obtaining satisfactory germination is often
. encountered. The former objection may gradually be removed as techniques in
producing triploid seed is improved to lower seed costs; the solution to the latter
problem is being investigated by this author. Preliminary results obtained in the
study of this problem along with general experimental production techniques employed
are reported herein.
1951 Experiment
Trial packages of the seedless varieties Asamiy and Asashin were received
from the japan Seed and Plant Company, Tokyo, japan, and the seedless variety
lll The author wishes to express his appreciation to Dr. j. G. Rodriquez, Dept. ofEn—
tomology & Botany, for the mite studies made in these experiments and the ensuing
development of successful methods for mite control.
Kentucky Agricultural Experiment Station
University of Kentucky
Lexington

 e. Z .. _1 .
Yamota starin No., 3 x Asahi from Fujita Seed Company, Ltd. , Osaka, Japan.
Instructions from these two seed companies included notes to maintain bed
temperatures at 300 C. (860F.) after planting and either cut off the taper peaks of
each seed or to soak in water. Actual techniques used to maintain this bed temperature
were not described.
Seed of each variety was divided into two lots. Taper peaks of each seed of ,
one lot of each variety were removed by rneans of a pruning shears while seeds of the
other lots were left intact. Seed was then planted on May 19 in Z" x 2. 1/2 " tar paper M
plant bands arranged in ordinary wooden flats. Rate of seeding was one seed per p
band. Steam sterilized soil used in these ba.nds was composed of two parts loam
soil, one part rotted manure and one part sand. All flats were placed in the green —
house on raised benches and thoroughly watered. Greenhouse day temperatures p
ranged as high as 950F.. and night temperatures as low as 70OF. Seedlings were
transplanted to the field on June 1...
Single seedlings were spaced three feet apart in a single row.. A row of a · A
regular watermelon variety (Stone Mountain Wilt Resistant No. 5) was planted on
each side of the row of seedless watermelons to effect proper pollination. Distance ·
between rows was 8 feet.
All plants were dusted with 3 percent purified DDT until vining. After vining V
had started, plants were sprayed with rnethoxychlor and zineb at the rate of 3 and 2
pounds respectively per l00 gallons of water.
RESULTS2
An average germination oi 75 percent was obtained with all three varieties.
There were no differences in percent. germination between seeds which had the i
taper peaks removed and those left intact.
Vine growth was luxuriant., ln general, there were no differences in the
length of runners of the seedless varieties and the regular variety used as the pol-·
linator.
The fir st ripe fruits were harvested August 10 (83 days after seeding) with
a large number ripening beiore September 1.. Fruits ranged from 6 to 12 pounds in
weight. Fruit quality was excellent with crisp, very sweet flesh of deep red color. ·
Rind appeared rather tough but extremely thin, with red color extending to less than
one-half inch from the rind.
Fruits varied from containing three or four vestigial seeds to perhaps several
dozen. These vestigial structures. however. were tender and could be eaten in the
same manner as the seeds in a slicing cuccumber. Hollow fruits were not found except i
in those that were extremely overripe.
No phytotoxicitv was observed from the dusts and sprays used in the disease
and insect control program
1952 Experiment
Perforrnance of the seedless watermelon varieties in 1951 showed considerable
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ment of pollinators in the field was needed before they could be recommended to
growers. The objectives of this experiment were to: (1) study the influence of
various seed treatments on germination, (2.) determine yielding ability, (3) continue
quality evaluation studies, and (4) develop a simple system for the interplanting of
a pollinator with seedless watermelons,
METHODS:
Although the experimental varieties provided in 1951 were excellent, it
seemed more logical to use only that seed which was commercially available to
growers from American seedsmen and sold not as a particular variety but merely
as Japanese seedless watermelons. Seed was purchased from Vaughan's Seed
Company, Chicago, Illinois.
Since concentrated sulphyric acid and sodium hypochlorite (Chlorox) have
been used to improve germination of certain seeds with very hard seed coats, these
materials as well as tap water were used as seed treatments, Seven lots of 10 seeds
each were placed in half-pint Mason jars, The following treatments were used: (1)
non-treated dry seed (check), (2) 24-hour soak in tap water, (3) 48 —hour soak in tap
water,( 4), (5), and (6) 1, 5 and 10-minute soak in concentrated sulfuric acid followed
by a thorough rinsing in tap water, and (7) 24-hour soak in l percent Chlorox followed
by a thorough rinsing in tap water,
After treatments were completed, all seeds were immediately planted on
Mayo in the same manner as used in the 1951 experiment, After planting, flats were
placed over electric heating cables buried one -half inch deep in soil in a raised green-
house bench and thoroughly watered. Bed temperature was thermostatically controlled
at 85OF, except when day temperatures in the greenhouse exceeded this value, Green-
house day temperatures for the 15-day test period ranged from 80°to 950 F,
Seedlings were transplanted to the field on May 2.3, at a spacing of 3 feet by
8 feet. Because the Japanese seedsmen recommended that about Z0 percent of the
field be planted to pollinator, a seedling of Stone Mountain Wilt Resistant No, 5 was
placed every fifth plant in the row, Since plants were check--rowed, this meant
1 every fifth row (at the three-foot distance) was a pollinating row,
Methoxychlor and zineb were used, as in the 1951 experiment, to control in-
sects and diseases, Later in the season Manzate was substituted for zmeb in the
spray program,
RESULTS:
A summary of the seed treatments and germination obtained are presented in
Table 1,
From the data it appears that soaks of 24 to 48 hours in tap water were the most
effective means of improving germination since these treatments both produced 100 per
cent emergence, The non—treated dry seed showed 70 percent emergence which ap-
proached the 75 percent emergence of dry seed in the 1951 experiment, lt is not under-
stood why none of the seeds treated one minute with concentrated sulphyric acid emerg 
while those treated for 5 and 10 rninutes with concentrated sulphyric acid showed 90 and

 `\~ -
- 4 .. `
30 percent emergence, respectively. Although the 5-minute sulphuric acid treatment .
showed 90 percent emergence, seedlings from this treatment as well as those soaked
10 minutes were weak and emerged three to four days later than those from the water
treatments. Seedlings from Chlorox treated seeds showed 80 percent emergence, but
they were definitely stunted.
An extremely heavy infestation of the two-spotted spider mite caused so much
vine injury that it was impossible to secure even a fair approximation of fruit yields. T
Parathion sprays were used in an attempt to control mites with the manganese salt of M
ethylene bis dithiocarbamate (Manzate) being used as a fungicide., Vine injury, however,
appeared to become more severe with each succeeding spray. No disease was found -
which could account for this injury; hence, at the time this damage was thought to be
due to a parathion phytotoxicity.
First ripe fruits were harvested July 24th.E¤62 days after transplanting or 78
days after seeding. Fruit weights ranged from 6 to 12 pounds with an average weight
of 8 pounds. These data were obtained from harvests made rather early in the season
while vine were still normal.
Fruit quality as in 1951, was excellent. Hand refractometer readings of ripe i
flesh showed an average soluble solids content of approximately 10 percent.
ln harvesting it was noted that the underside, exterior color changed from
white to cream to deep yellow as fruits reached maturity., Fruits showing an under-
side color of deep yellow were actually over-ripe, while those showing a cream to
very light yellow were of a maturity consistent with excellent quality. This change
in underside color was found to be a very reliable index to harvesting fruits at peak
quality.
lnterplanting a row of Stone Mountain Wilt Resistant No. 5 every fifth row (at (
the three—foot distance) was found to be a simple plan of intermingling the pollinating
variety with the seedless variety. This particular pollinating variety, however, was
definitely later maturing than the seedless variety and produced fruits in this experi-
ment which were only fair in quality,
Vines early in the season made excellent growth and completely covered the
ground between rows. It appeared from this experience that the 3 feet by 8 feet
spacing might actually be Yoo close.
A brief summary of this experiment was previously reported by Klinker.
(Ky. Agr. Exp. Sta. Ann. Rpt. , 1952.)
1953 Experiment
Although the techniques developed for obtaining suitable germination and the 1
development of a simple system for interplanting the pollinator were very encouraging
in the 1952 experiment, the serious problem of mite control remained to be solved
before an acc;ura·i,e estimation of yielding ability could be made, The use of Stone
Mountain Wilt Resistant No. 5 was also considered to be an unsatisfactory pollinating
variety under the conditions tested. The objectives of this experiment, then, were
to: (1) develop a control program for mites, (2) seek an earlier maturing pollinating
V3l'l€t which would  T dufi   ••·  .  Lt ` its w f` i I •- n .- -  `··~ 

 - 5 -
ability, and (4) continue studies of germination and quality evaluation.
METHODS: 5
Seed described only as "Seedless watermelon" was purchased from Joseph
Harris Company, Inc. , Rochester, New York. This seed was soaked in water for
24 hours and planted in the greenhouse on April 29 exactly in the same manner as
used in the 1952 experiment.
All seedling were transplanted to the field at a spacing of 3 feet by 10 feet.
The earlier maturing varieties Rhode Island Red and Honey Cream were used as
pollinators. Arrangement of pollinators was the same used in the 1952 experiment,
i. e. , a pollinator every fifth plant in the row.
All plants were dusted at 5-day intervals with 7 1/2 percent methoxychlor to
control insects. Manzate was used as a fungicide in the first spray, but it became
evident that manzate was phytotoxic to watermelons ( and to cucurbits in general),
so this material was replaced by zineb in all succeeding sprays.
After it was learned that vine injury was being caused by the manzate
fungi; ide rather than by parathion (as believed in the 1952 experiment), dusts of
l percent parathion and 5 percent malathion were tested for the control of mites.
RESULTS:
Soaking seed for 24 hours in water and germinating in wooden flats over
electric cables in the greenhouse gave from 95 to 100 percent emergence of seed-
lings.
An extremely heavy mite population developed rather uniformly throughout
the plantings within two weeks after vining had started. This build-up in mite
population occurred with such tremendous rapidity and intensity that considerable
vine injury resulted before the mite control dusts could be applied. Once the dusts
had been applied, however, excellent control was obtained. Mite counts made 4
days after dusting showed that l percent parathion dust gave 100 percent control of
the active forms of mites, while 5 percent malathion gave 95 percent control of the
y active forms. These results suggest that although 1 percent parathion dust was very
effective in controlling mites, a regular dusting program must be started as soon as
the watermelons start to vine if mite injury is to be completely eliminated. Dust
applications of parathion before vining cannot be recommended because it may be
phytotoxic to watermelons in this early stage of growth. Since mites congregate
almost entirely on the underside of leaves, it is believed that dusting will effect a
better control of mites than spraying on such a low growing crop as watermelons.
Although the 5 percent malathion dust was not quite as effective as the 1 percent
parathion dust, a regular program of dusting with 5 percent malathion would also
appear to be a practical method for controlling mites. For those who are not pre-
pared to take all the necessary precautions in using l percent parathion dusts, the
5 percent malathion dust is probably preferable since it is far less toxic than parathion
to warm-blooded animals.
First ripe fruits were harvested 80 days after seeding. Yields obtained in this
experiment averaged close to two melons per plant. This yield is considered to be

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very low since vines were not only injured by mites, but this injury was probably
itensified by the extreme drouth which p_revailed throughout much of the season. .
Fruit quality as in preceding years, was excellent. The change in under-side
color of the fruits from white to cream to light yellow was again found to be an
excellent index to harvesting fruits at peak qualityr,
Fruits produced by the pollinating varieties Rhode Island Red and Honey
Cream were of good quality, but they could not compare favorably with the 1
excellent quality of the seedless watermelons. Both of these varieties matured much _
earlier than had Stone Mountain Wilt Resistant No. 5 in past experiments.,
Vine growth compared favorably with that produced in the 1952 experiment, but
it appears that increasing the distance between rows from 8 to 10 feet was unnecessary,
particularly if vines are "rowed" even once. .
Reports from over 100 people who tasted the seedless watermelon from this g
experiment were very favorable as to quality and flavor, The School of Home
Economics considered the rather small size as a definite advantage considering the
ease of storing in a home refrigerator and the fact that one melon cut in four parts p
made very desirable—sized servings.,
SUMMARY ‘
Results of the experiments discussed in this report may be summarized as
follows;
1. Fruits produced during three years of trial were consistently of excellent in _
quality with crisp, very sweet flesh of deep red color which extended to less than one-
half inch from a thin, but rather tough rind,. Under the conditions of these experiments, V
seedless watermelons started ripening 78 to 83 days after seeding,
2. Fruit size ranged from 6 to 12 pounds in weight, averaging approximately
8 pounds. Melons of this size can be stored much more easily in the home refrigerator
than can the larger melons of regular varieties, When cut in four parts, very desirable-
sized servings are obtained,
3. Soaking seed for 2.4 hours in tap water was found to be the best and simplest
of the seed treatments tried to bring about satisfactory germination,. After soaking,
seed must be planted immediately in soil maintained at a minimum of 85°F, to insure
satisfactory emergence.,
4. Although seedlings were produced in the greenhouse, it may become
feasible to produce them in electric hotbeds, Further experimental work is also
planned to determine some method of producing seedless watermelons by direct field »
seeding.
· 5. Considerable emphasis was placed on the serious mite problem experienced
in growing seedless watermelons on the Station Farm, but this problem may not be at
all serious in other areas, particulary if they are grown in locations which are
remote from apple orchards and other perennial fruit plantings lf mites become a

 malathion, may be expected to give practical control of this pest.
6. Yielding ability, because of the continual mite problem was never ac-
curately estimated, Yields of approximately two fruits per plant were obtained in
the 1953 experiment, but these yields were considered very low because of mite
and drouth injury. Under favorable growing conditions yields per plant many con-
ceivably be double or treble this yield, but further trials under more favorable con-
ditions are contemplated to secure a reliable estimate of yielding ability under
Kentucky conditions.
7. The change in the underside color of seedless watermelons from white
to cream to light yellow wasfound to be a reliable index to harvesting fruit at peak
quality. ‘
8. Probably the only great disadvantage to seedless watermelons is the
high cost of seed. Improved breeding techniques may eventually reduce these costs
to some extent. If heavy yields of this excellent quality melon can eventually be ob-
tained, returns may be sufficiently high to fully justify the high cost of seed.
9. Spacing of single plants 3 feet by 8 feet (2.4 square feet per plant) was
found to be sufficient area for the production of an excellent vine.
l0. Interplanting a row of the variety Rhode Island Red or Honey Cream
every fifth plant in the row (or every fifth row at the 3—foot spacing) was found to be
a simple plan for intermingling the pollinating variety with the seedless melons. These
two pollinating varieties not only matured nearer to the ea‘rly—maturing seedless ‘
melons than did Stone Mountain Wilt Resistant No. 5, but their fruits were of better
quality. ’
RECOMMENDATIONS FOR GROWING SEEDLESS WATERMELONS
Although it is not yet possible to make unqualified recommendations in
growing seedless watermelons, the following plan based on three years of experimental
work can be used by those who wish to make a small trial planting:
Two to three weeks before transplanting to the field, soak seed in a tumbler
I of tap water for Z4 hours, remove frorn water and plant immediately in pots or bands
at least Z inches in diameter which previously have been arranged in wooden flats.
Do not plant seed deeper than 1/4 inch. Place flats of the planted pots or bands over
electric heating cables buried about one —half inch deep in sand or soil in a green-
house bench or hotbed, thermostatically maintaining a soil temperature of 85OF.
After seedlings have developed at least one true leaf, and after all danger
of frost has passed, transplant to fertile soil in the garden or field. Space single
plants 3 feet apart in the row. Use a transplant of a regular watermelon variety
such as Rhode Island Red or Honey Cream (yellow~fleshed) every fifth plant in the
row (every fifth row at the 3-·foot distance) to insure proper pollination. Adlow
a distance of at least 8 feet between rows. Water each transplant with one pint
of water after carefully removing the transplant from the plant band or pot and
placing in a hole about 3 inches deep. After watering, draw soil around transplant
and press firmly.

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Although subject to further evaluation, the following pest control program
may be used: Dust each plant immediately after transplanting with a light coating »
of 7 1/2 percent methoxychlor or 3 percent purified DDT. Repeat this dusting
every 5 days until plants start to vine. After vining starts, dust every 7 days with
a mixture containing 1 percent parathion (or 5 percent malathion) and 8 percent
zineb until end of the season.
Approximately 75 days after seeding, examine underside color of the larger —
watermelons for a change in color from white to cream or light yellow. This color
change is generally a very reliable means of determining that melons are ripe, but '
before picking a large number of fruits, cut one or two melons to check the reliability rv
of this method of determining fruit maturity under your conditions.
LITERATURE CITED
Kihara, H. Triploid watermelons, Amer. Soc. Hort. Sci. Prod. 58:217-30. 1951 ·
Ky. Agr. Expt. Sta. A
1952. The experimental production of seedless watermelons, ·
65th Ann. Rpt., p. 58. · A
Table 1 - Percent emergence calculated
15 days after planting. Y
Treatment Percent Emergence `
1. Non treated dry seed (check) 70
2, One —minute soak in conc. sulfuric acid 00
3. Five -minute soak in conc. sulphuric iicid 90
4. Ten—minute soak in conc. sulfuric acid 30 A
5. Twenty -four hour soak in tap water 100
6. Forty —eight hour soak in tap water 100
7, Twenty —four hour soak in 1 percent chlorox 80