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c'rS3m G6 Central Science
GULF COAST RESEARCH & EDUCATION CENTER MAR G 1990
IFAS, UNIVERSITY OF FLORIDA
5007 60TH STREET EAST
BRADENTON, FL 34203 University of Florida
Bradenton GCREC Research Report BRA1989-24 August 1989
FUSARIUM WILT AND DAMP OFF OF ASTER AS AFFECTED BY LIME
AND MICRONUTRIENTS IN ARTIFICIAL MEDIA
S. S. Woltz and A. W. Engelhard1
One of the most pervasive and unpredictable problems with aster production
as cut-flowers or bedding plants is that of Fusarium wilt incited by
Fusarium oxysporum of sp callistephi. We do not know of any true monogenic
resistance but rather there are varying degrees of tolerance of cultivars to
Fusarium wilt and varied virulence of strains of the pathogen against
cultivars of Callistephus chinensis, the common China aster. The lack of
any true resistance is exemplified by a potential problem of damping-off
wherein the pathogen invades the cortex and is more rapidly damaging than
the common vascular wilt.
Experience with chrysanthemums (2,3,4) and asters (1,3) together with recent
developments in the horticulture of asters (new cultivars and their use in
pots, bedding and as cut flowers) prompted us to renew research with
Fusarium oxysporum f. sp. callistephi in artificial media culture with
factorial combinations of 3 levels each of lime and Perk micronutrient mix.
The object was to select cultural procedures that would allow the use of
this popular horticultural crop with much reduced risk of crop failure.
Materials And Methods
'Perfection' asters were seeded 8 per 6" pot which contained 1:1 Florida
sedge peat:vermiculite June 22, 1989. The potting medium was amended with
powdered technical grade CaCO3 and Perk micronutrient mix. Perk contains
the following percentages of nutrient elements: magnesium, 5.0; manganese,
2.0; copper, 0.5; zinc, 1.0; iron, 9.0; boron, 0.02; and molybdenum, 0.003.
Table 1 lists the rates and combinations of treatments.
Treatments were randomized by replications, 4 replicates per treatment.
After seedlings were established (July 10), Fusarium microspores, 50 million
in 150 ml, were poured on the surface in each pot. Roots were not wounded.
Also, 3g 14-14-14 Osmocote top-dressing was applied to each pot. Disease
developed very rapidly and data were taken July 19 on the number of
seedlings diseased per pot and the average fresh weight per seedling.
Seedlings were pulled so as to include the roots and rinsed to aid in
evaluating disease symptoms that included browning and necrosis of roots and
1Professor of Plant Physiology & Professor of Plant Pathology, respectively.
Table 1. Ca CO3 and Perk factorial combinations for aster Fusarium wilt
Treatment Perk Ca CO3
No. Ibs. per cu. yd. Ibs. per cu. yd.
1 0.6 1.7
2 1.7 1.7
3 5.0 1.7
4 0.6 5.0
5 1.7 5.0
6 5.0 5.0
7 0.6 15.5
8 1.7 15.5
9 5.0 15.5
Note: Medium also contained 6 Ibs 14-14-14 Osmocote and 1.7 lbs MgSO4.7H20
per cu. yd. of medium.
A second crop, 10 seeds per pot, was planted July 24 in the same pots.
Seedling emergence/survival data were collected August 1, 4, 8 and 14. A
third crop was planted August 29 as seedling transplants, 8 transplants per
pot. Disease ratings were made September 8.
Results And Discussion
The percent plants diseased (Table 2) reveals a very high degree of pathogen
virulence and/or aster susceptibility. The highest level of lime
application resulted in a sharp reduction in disease but there was no
difference between the low and intermediate levels. The pattern of attack
of the Fusarium was such that all tissues appeared to be susceptible to
damage: stem, roots, crown, petiole and leaf blade This type reaction
makes the combination of host and pathogen useful for the investigation of
the physiology of the disease process, both in the soil and in the plant
relative to host and parasite nutrition.
Fresh weight data were collected for the aster seedlings shoot plus root.
Weights reflect the amount of root included when seedlings were pulled along
with the roots that remained attached. Decayed roots were largely left in
the pot. Average weights for seedlings were greater for intermediate and
high lime rates than for the low rate. This is in agreement with the
Re-plant emergence and survival was significantly reduced by the low lime
treatment. It could not be definitely established that the cause of poor
emergence was the Fusarium pathogen but the amount of early damp-off
indicated the probability that it was pathogen-related. Fusarium was
isolated from representative apparently diseased seedlings. Successive sets
of data on emergence/survivalt (counts of living plants) indicate rapid
disease development was highly favored by the low and intermediate lime
Data from the transplant crop (Table 2) show a strong reaction to lime
rates, with decreased disease with each increment of added lime. Perk
micronutrient mix levels had no effect in this experiment.
In summary, the data presented show that liming at increasingly higher rates
of powdered calcium carbonate decreased disease stepwise. Applications of a
micronutrient mix had no discernible effect on disease. An effective liming
procedure is, therefore, likely to be advantageous in reducing the often
serious problem of Fusarium wilt of asters. Effective lime use entails the
need to use adequate but not excess amounts of lime, having an intimate
mixture of lime, finely ground or powdered so as to be quickly reactive and,
finally, to dry-mix and then have adequate moisture present to promote the
neutralization of acidity. Precautions should be taken to avoid getting the
pH too high (above pH 7.0) and to provide adequate micronutrients,
particularly iron since asters are easily subject to iron deficiency.
Adequate liming should be incorporated into the disease control program as
an effective aid to the usual practices of sanitation and exclusion of the
The capable technical assistance of Patricia Cox is gratefully acknowledged.
1. Engelhard, A. W. (1975) Aster Fusarium wilt: Complete symptom control
with an integrated fungicide-N03-pH control system. Proc. Am.
Phytopath Soc. 2:62 (Abstr).
2. Engelhard, A. W. and Woltz, S. S. (1972) Complete control of Fusarium
wilt of chrysanthemum with chemotherapeutants combined with a high lime
and nitrate-nitrogen culture regime. Phytopathology 62:756.
3. Engelhard, A. W. and Woltz, S. S. (1978) Effect of temperature,
nitrogen source, lime and benomyl treatments on Fusarium wilt of
chrysanthemum, aster, and gladiolus. Third Int. Congress of Plant
Pathology, p. 375 (Abstr).
4. Woltz, S. S. and Engelhard, A. W. (1973) Fusarium wilt of chrysanthemum:
Effect of nitrogen source and lime on disease development.
Table 2. Effect of perk micronutrient mix and powdered calcium carbonate on Fusarium wilt/damp-off and
seedling growth in Fusarium inoculated media.
plants Percent survival Disease
Powdered diseased Fr. Wt. of seedlings ratingx
Calcium first" of at various dates, third crop
Trt. Perk Carbonate crop Asters second crop transplants Media
No. Ibs/cu.yd. 1bs/cu.yd. 7-18 g/plant 8-1 8-4 8-8 8-14 9-8 pH
1 0.6 1.7 81 4.5 38 13 3 0 1.50 5.84
2 1.7 1.7 90 4.7 38 15 3 0 1.84 5.81
3 5.0 1.7 85 4.9 33 0 0 0 1.44 5.79
4 0.6 5.0 96 6.2 75 28 8 0 0.91 5.81
5 1.7 5.0 82 4.9 50 15 8 3 0.84 6.05
6 5.0 5.0 59 6.5 60 18 3 3 0.56 5.71
7 0.6 15.0 20 6.6 63 38 13 0 0.03 6.40
8 1.7 15.0 31 7.0 83 33 23 8 0.09 6.39
9 5.0 15.0 16 5.5 95 73 53 23 0.82 6.57
LSD, 5% level 30 2.8 38 13 14 -Y 0.81 0.23
0.6 66a 5.8a 58az 26ab 7.5b 0.81a 6.01a
1.7 68a 5.5a 57a 21b 11b 0.93a 6.08a
5.0 53a 5.6a 63a 30a 18a 0.70a 6.02a
1.7 85a 4.7b 36b 9.2c 1.7b 1.59a 5.81b
5.0 79a 5.8a 62a 20b 5.8b 0.77b 5.85b
15.0 22b 6.4a 80a 48a 29a 0.07c 6.45a
ZMeans followed by a different letter are significantly different at the 5% level.
YInsufficient data to permit statistical comparisons.
XFusarium disease rating: 0 = none, 1 = moderate wilt, 2 = severe wilt and necrosis, and 3 = dead.
WThree plantings were made sequentially. The first and second were seeded in the pots, the third was
transplanted. Pots were inoculated only after the first seeding.