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Institute of Food and Agricultural Sciences
Gulf Coast Research and Education Center
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Bradenton GCREC Research Report BRA1993-25
Effect of Lime, Nitrogen Source, and Sodium Chloride on Crown-.;,, ,>,, .
and Root Rot of Lisianthus incited by Fusarium solani,. ,7
S. S. Woltz, B. K. Harbaugh, A. W. Engelhard, and J. P. Jones'.
A very destructive disease of Eustoma grandiflorum (Raf.) Shinn. (Lisianthus) has'"
been encountered regularly in Florida for a number of years. The condition is
best described as a crown and root rot apparently incited by Fusarium solani
(Mart.) Appel & Wright. In normal culture in the field and greenhouse there has
been a variable incidence of the disease occurring in a relatively random
manner. Fusarium solani was isolated repeatedly from affected plants. The
isolates were effective in producing the symptoms when inoculated onto Eustoma
seedlings and cuttings. The Fusarium was recovered following inoculation.
During the course of greenhouse and field experiments as well as in commercial
production, it was observed that a crown and root rot of unknown etiology was a
serious problem in the production and research with Eustoma. Research was
therefore undertaken to determine the cause and methods of control of the
disease, attempting to parallel previous work on cultural methods of controlling
Fusarium oxvsporum diseases (Woltz and Jones, 1973, 1981). This report presents
results of experiments designed to identify and develop cultural methods of
ameliorating a disease problem with Eustoma.
Materials and Methods
Koch's postulate procedures were performed by isolating the causal organism,
Fusarium solani (Mart.) Appel & Wright, on a selective medium (Komada, 1975) and
inoculating crown and root wounded Eustoma seedlings; unrooted cuttings were also
inoculated by dipping the cut end in a suspension of conidia of the Fusarium and
putting them to root in trays of peat-vermiculite mix covered with plastic film
and placed in a plant growth chamber. F. solani was identified by P. E. Nelson
(Nelson, et al., 1983). Six week old seedlings were inoculated by root and crown
wounding and dipping into a suspension of 20.106 conidia per ml of Fusarium. They
were transplanted two per container into 12.5 cm diameter plastic pots containing
approximately 1 liter of a 1:1 mix of Canadian peat:vermiculite. The medium was
amended with 1.5 kg.m" of Perk micronutrient mix and 3.0 kg.m of single
superphosphate. Factorial combinations of CaCO3 (1 or 5 kg.m ), (CaNO,)22 or
(NH4),SO4 each at 300 mg.liter" N, NaCl at 0 or 3500 mg.liter" and plant
inoculation or noninoculation constituted the experimental treatments. CaCO was
included in the dry mix while N and NaCl solutions at 150 ml per pot were applied
'Visiting Professor, Professor (Floriculture), Professor Emeritus, and Professor
(Plant Pathologist), respectively.
before planting and weekly thereafter for-thT duration of the experiment. K was
supplied as KC1 at the rate of 175 mg.liter in nutrient solutions. Containers
were irrigated as required with water containing 100 mg.liter"' Ca and 2O
mg.liter- Mg with a pH of 7.7 and total salts content of 600 mg.liter.
Greenhouse temperatures ranged from 230 to 270C daytime and 190 to 220C at night.
At the conclusion of the experiment crown chips of tissue were plated out on
Komada agar to check for the presence of F. solani.
Noninoculated cuttings rooted normally while those that were inoculated developed
a severe basal stem rot and failed to develop roots. Disease developed slowly
in the inoculated seedlings over a six week period. Symptoms included a brown
rot of the crown and roots. Death of some seedlings occurred. Early symptoms
of the disease are mild and difficult to rate objectively. Apparently the
progress of the disease process must reach an advanced stage to produce overt,
readily recognizable symptoms. The progress of crown and root rot of Eustoma is
similar in this regard to stem rot of chrysanthemum which is also incited by F.
solani (Engelhard et al., 1976). The pathogen was recovered from Eustoma in each
case by plating out chips of tissue on Komada agar (Komada, 1975).
Treatments including the high rate of CaCO, and Ca(N03)2 as the nitrogen source
enhanced growth of Eustoma seedlings as measured by fresh weight of plant tops,
and root quality. Effects of inoculation were ameliorated by these treatments.
Root damage due to Fusarium was lessened by the high level of CaCO3 when the
source of N was either Ca(N03)2 or (NH) 2SO4. Plant height was adversely affected
by the (NH4)2SO source of N in combination with inoculation with Fusarium.
Disease ratings were also higher under these conditions. Symptomatically, the
effects of the Fusarium were to cause a wilting, chlorosis and scorch of the
foliage. Roots were reduced in amount of growth and were discolored (brown) and
partly decomposed. The NaCl variations had no effect on growth of plants or
disease. One chip from the crown of each plant was cultured on Komada agar. The
noninoculated plants had a F. solani isolation rate of 0.4% while inoculated
plants had 61.3% finding of F. solani.
The inoculum level and inoculation technique employed were sufficiently stringent
to produce clear disease response and definition of cultural factors affecting
the disease response. Crown and root rot is slow to develop, apparently because
of a high level of resistance on the part of Eustoma and also because of a
possible tendency to remain latent until conditions are ripe for development of
the disease. Crown and root rot of Eustoma is a serious problem that is
difficult to recognize due partly to the failure for symptom expression to occur
early enough to afford early diagnosis. The first warning may be a wilting and
rapid decline of mature plants followed by the death of seriously affected
plants. Symptomatic plants usually yielded F. solani upon being cultured.
Frequently the culturing of stem chips of apparently healthy plants yielded F.
solani. Follow-up observation has not been adequately employed to ascertain how
latent Fusarium will become active or what the conditions of the host must be to
elicit the expression of symptoms. Crown and root rot may be an economic problem
as the crop matures. Also, indications from these results are that important
considerations in disease avoidance and high quality production of Eustoma
include the use of adequate lime and the preferential use of higher levels of
nitrate as the major N source as well as the provision of higher levels of
soluble Ca in the nutritional program. These nutritional procedures are deemed
to be especially beneficial
(Harbaugh and Woltz, 1991;
horticulturally as well as
to Eustoma on the basis of plant growth and quality
Frett, et al., 1988) so that their use is preferred
from the disease standpoint.
1. Engelhard, A. W., G. L. Crane, and H. C. Mellinger. 1976. Stem rot, a
new disease on chrysanthemum incited by Fusarium solani. Plant Disease
2. Frett, J. J., J. W. Kelly, B. K. Harbaugh, and M. Roh. 1988. Optimizing
nitrogen and calcium nutrition of Lisianthus. Commun. Soil Sci. & Plant
3. Harbaugh, B. K. and S. S. Woltz.
affected by low pH of root medium.
1991. Eustoma quality is adversely
HortScience 26: In press.
4. Komada, H. 1975. Development of a selective medium for quantitative
isolation of Fusarium oxvsporum from a natural soil. Rev. of Plant
5. Nelson, P. E., T. A. Toussoun, and W. F. 0. Marasas. 1983. Fusarium
species: An illustrated manual for identification. Pennsylvania State
Univ. Press, University Park. 193 pp.
6. Woltz, S. S. and J. P. Jones. 1973. Interactions of nitrogen fertilizers
and liming procedure in the control of Fusarium wilt of tomato.
7. Woltz, S. S. and J. P. Jones. 1981. Nutritional requirements of Fusarium
oxvsporum: Basis for a disease control system. In: Nelson, P. E., T. A.
Toussoun, and R. J. Cook. Fusarium: Diseases, Biology, and Taxonomy. The
Pennsylvania State Univ. Press, University Park and London. pp. 340-349.
Table 1. Effect of CaCO, level, N source, NaCL and inoculation with F. solani on growth and disease of Eustoma seedlings.
CaCOa tops Root rating Plant height Disease rating
kg.m- NaCI pH of 0-10y cm 0-4'
medium N source mg.liter' media NI' I NI I NI I NI I
1 A' 0 4.56 d 20.8 c" 3.5 d 1.0 efg 0.1 efg 17.5 ab 8.0 c 0.13 c 3.00 a
1 A 3500 4.61 d 22.0 c 5.3 d 0.9 fg 0.2 g 17.3 b 8.8 c 0.00 c 2.25 b
1 N 0 5.47 c 39.3 ab 20.0 c 2.5 de 1.5 efg 23.8 ab 20.5 ab 0.00 c 0.00 c
1 N 3500 5.74 c 33.8 b 20.3 c 3.3 cd 2.0 def 23.0 ab 22.8 ab 0.38 c 0.00 c
5 A 0 6.26 b 40.5 a 23.3 c 4.8 bc 2.0 def 23.8 ab 19.5 ab 0.13 c 0.00 c
5 A 3500 6.37 b 44.8 a 24.5 c 5.0 b 2.3 def 23.8 ab 23.8 ab 0.25 c 0.00 c
5 N 0 7.26 a 42.3 a 25.0 c 4.8 bc 3.3 cd 26.3 a 24.0 ab 0.00 c 0.00 c
5 N 3500 7.21 a 42.8 a 26.8 c 6.5 a 4.3 bc 24.0 ab 24.5 ab 0.00 c 0.00 c
'NI = noninoculated controls; I = inoculated.
YRating of root ball: 0 = no roots at edge of pots; 10 = most abundant roots of good quality.
'Rating of disease by plant wilt and stem and root discoloration: 0 = no disease; 4 = dead.
"Numbers followed by different letters differ significantly by Duncan's test at the 5% Level. Values not followed by letters are not significantly
different in their category.
'A = (NH.),SO,, 300 mg N.titer-; N = Ca(N03),, 300 mg N.liter-'.