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GULF COAST RESEARCH & EDUCATION CENTER
IFAS, UNIVERSITY OF FLORIDA
5007 60th Street East
Bradenton, FL 34203
Bradenton GCREC Research Report BRA1989-20 August 1989
Library FSARIUM WILT OF CHARLESTON GREY WATERMELON AS
I FLUENCED BY LIME AND MICRONUTRIENT AMENDMENTS
MAR G 1990
S.S. Woltz and J.P. Jonesl
University of Florida
FuTsarum wi t, caused by Fusarium oxysporum f. sp. niveum, is a persistent
problem in watermelon culture because there is no true resistance in
available cultivars. The common practice among growers is to move to new
fields every year or two to grow watermelons, which involves high land
preparation costs as part of the production budget. After a resting
period of 5 7 years, fields are planted again to watermelons.
Transplants, if used to sell on an early market, are usually planted in
artificial media. Whether these media are as subject as soil to the
effects of infestation with virulent Fusarium is not known. Consequently,
studies with artificial media need to be made to evaluate the disease
potential from chance contamination since it would be relatively easy to
mass inoculate a seedling house by unsanitary practices. Also, sterile
materials generally are more subject to the effects of chance inoculation
than non-sterile media because of the antagonistic and competitive actions
of resident microbial populations in non-sterile media. Additionally,
peat, especially Florida sedge peat, may present a problem in uniform pH
adjustment. Our experience at GCREC has been that uniform adjustment of
sandy soils to higher pH's, 7.0 to 7.5 will greatly reduce the severity
of the problems with Fusarium wilt of watermelon, as well as with many
other horticultural crops (1-6).
The present study was carried out to determine whether varied levels of
micronutrient amendment at a range of pH's in an artificial medium would
affect the severity of Fusarium wilt of watermelon seedlings.
Materials and Methods
A mixture of Florida sedge peat and vermiculite, 1:1 by volume, was
amended with 9 combinations of lime (powdered CaC03) and Perk
micronutrient mix, Kerr-McGee, Oklahoma City, OK. Lime levels were 1, 3,
and 9 grams per liter of mix; Perk levels were 0.33, 1, and 3 grams per
liter of mix. Perk contains 5% magnesium, 2% manganese, 0.5% copper, 1%
zinc, 9% iron, 0.02% boron, and 0.003% molybdenum. All mixtures included
3.5 grams of 14-14-14 Osmocote and 1 gram of MgSO4.7H20 per liter. The 9
treatments were randomized in each of 4 replicates placed so as to account
1Professor of Plant Physiology and Professor of Plant Pathology,
for the variability of growth and disease development in the pad-fan
cooled greenhouse which has a temperature gradient increasing from North
Charleston Grey watermelon seeds were planted 3 consecutive dates in a 1:1
v/v mixture of Florida sedge peat:vermiculite in 6-inch plastic
containers. Seeding dates were June 16, 28 and July 20, 1989. Pots were
inoculated June 23 and July 12 with approximately 50 million microspores
of F. oxysporum f. sp. niveum per pot at each inoculation. Pots were
top-dressed with 2 grams of Osmocote 14-14-14 per pot July 14. The second
planting was made before seedlings of the first seeding were removed for
disease assay. To evaluate incidence of disease, seedlings were pulled
with roots attached; roots were washed in water and a count made of
numbers of seedlings with visible browning of roots or stems. Fresh
weights were taken and weight per seedling was calculated. Media samples
were collected at the end of the experiment and pH was determined in 1:1
media:deionized water. Disease counts were made July 7, 14, and August
1 based on the percent of emerged plants that were dead or showed browning
of roots or stem. Wilt was always associated with any significant degree
Results and Discussion
Data from the first planting (Table 1) indicate that the highest lime
level had less disease than the intermediate and low levels. Fresh
weights of seedlings were higher with the high lime level, indicating the
disease was sufficiently severe to reduce fresh weights. The second crop
of seedlings which had been started as an interplanting in the first crop
was more severely affected. Also, the disease control due to lime was
lost. Two possible explanations are suggested for the interplantingg"
effect. One is that the germinating seeds were made more disease prone
owing to the presence of watermelon roots and their exudates. Roots of
seedlings may exude sugars, amino acids and other metabolites that could
reverse the benefit of the lime, favoring the Fusarium in disease
production. A second possible explanation is that the removal of the
first batch of seedlings by uprooting wounded the roots of the second
crop; root wounding in the presence of high inoculum levels would be very
likely to enhance disease.
Data from the third seeding (not an interplanting) indicate a good
separation of disease response to lime. Each increment of lime increase
resulted in decreased disease. Fresh weights of seedlings, however, were
reduced only by the low level of lime.
Response to micronutrients occurred in the third planting which showed a
significant difference between treatments 4 and 6, the low and high rates
of Perk. Thus, in this case with the intermediate rate of lime, the high
level of Perk apparently was more conducive to disease than was the low
rate. This is similar to other observations which we have made (1,3,4,6)
for micronutrients in general but for zinc in particular.
In summary, it was shown that Fusarium wilt of watermelon seedlings
growing in a peat-vemiculite mix may be effectively reduced in incidence
and severity by application of powdered calcium carbonate. In one
comparison, high versus low Perk micronutrient was more conducive to
disease, possibly by improving the nutrition of the pathogen. Since
Florida sedge peat has a large reserve of acidity, it makes a good medium
to test the feasibility of quickly and uniformly neutralizing aciaity with
powdered calcium carbonate.
The capable technical assistance of Patricia Cox is gratefully
1. Jones, J. P. and S. S. Woltz. 1972. Effect of soil pH and
micronutrient amendments on Verticillium and Fusarium wilt of tomato.
Plant Dis. Reptr. 56:151-153.
2. Jones, J. P. and S. S. Woltz. 1975. Effect of liming and nitrogen
source on Fusarium wilt of cucumber and watermelon. Proc. Fla. State
Hort. Soc. 88:200-203.
3. Jones, J. P. and S. S. Woltz. 1981. Fusarium-incited diseases of
tomato and potato and their control. In: Nelson, P. E., Toussoun, T.
A. and Cook, R. J. (eds.) Fusarium: Diseases, Biology and Taxonomy.
Penn State Univ. Press, University Park, pp. 157-168.
4. Woltz, S. S. and J. P. Jones. 1968. Micronutrient effects on the in
vitro growth and pathogenicity of Fusarium oxysporum f. sp.
lycopersici. Phytopathology 58:336-338.
5. Woltz, S. S. and J. P. Jones. 1973. Tomato Fusarium wilt control by
adjustments in soil fertility. Proc. Fla. State Hort. Soc. 86:157-159.
6. Woltz, S. S. and J. P. Jones. 1981. Nutritional requirements of
Fusarium oxysporum: Basis for a disease control system. In: Nelson,
P. E., Toussoun, T. A. and Cook, R. J. (eds.) Fusarium: Diseases,
Biology and Taxonomy. Penn State Univ. Press, University Park, pp.
Table 1. Effects of lime and micronutrients on watermelon Fusarium wilt.
First Planting Second Planting Third Planting
Diseased Av. Fr. Wt. Diseased Av. Ft. Wt. Diseased Av. Ft. Wt.
Treatment Perk CaC03 Plants per plant Plants per plant Plants per plant Media
No. g/L g/L % 9 % 9 % 9 pH
1 0.33 1 37.5 4.3 54.2 1.9 72.4 3.4 5.80
2 1 1 16.8 6.4 37.5 1.9 67.6 2.8 5.73
3 3 1 25.3 5.1 50.0 1.1 75.1 2.5 5.67
4 0.33 3 12.5 6.3 36.3 1.9 33.5 4.3 6.33
5 1 3 12.5 5.9 45.8 1.8 42.3 5.1 6.33
6 3 3 16.8 5.0 55.8 1.9 68.7 3.6 6.21
7 0.33 9 8.5 6.7 39.2 2.2 1.9 4.2 7.27
8 1 9 0 7.4 66.7 1.5 0 4.7 7.68
9 3 9 0 6.5 60.4 1.9 0 5.7 7.59
LDS, 5% level 23.2 1.8 NSD NSD 26.0 1.4 0.30
0.33 19.5a* 5.8a 43.2 2.0 35.9a 4.0a 6.47a
1 9.8a 6.5a 50.0 1.7 36.6a 4.2a 6.58a
3 14.0a 5.5a 55.4 1.6 47.9a 3.9a 6.49a
1 26.5a 5.3b 47.2 1.6 71.7a 2.9b 5.73c
3 13.9ab 5.7b 46.0 1.8 48.2b 4.3a 6.29b
9 2.8b 6.9a 55.4 1.9 0.64c 4.8a 7.51a
XValues in same column followed by different letters are significantly different at the 5% level.