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Temperature and Potting Medium CompositionCAlj tcience
Rhizoctonia Aerial Blight of B6ston Fern Library
A. R. Chase and C. A. Conover
University of Florida, IFAS OCT 14 1987
Agricultural Research and Education Center Apopka
AREC-Apopka Research Report, R-86-4fiversity of Florida
Aerial blight, caused by Rhizoctonia solani, occurs on many Florida
foliage plants. The fungus grows onto stems or foliage in contact with the
potting medium when conditions are favorable. Foliage infections often
continue to occur when the spider web-like mycelia move from one section of
the foliage to another. Little, if any disease, develops in Florida during
the cooler months of the year.
Air temperature can affect severity of foliar diseases of foliage
plants such as Myrothecium leaf spot of dieffenbachia (1). Air and potting
medium temperatures may affect development of Rhizoctonia aerial blight
since the pathogen is a soil-borne organism which causes a foliar disease.
No research was found that elucidated effects of air temperature or potting
medium temperature on severity of this disease on a foliage plant.
Therefore, this study was initiated to evaluate the effects of three
potting media commonly used in Florida ornamental production and potting
medium and air temperatures on growth of 'Fluffy Ruffle' (Boston fern) and
development of aerial blight caused by R. solani.
Experiment 1. The first experiment evaluated effects of potting medium
composition and temperature on Rhizoctonia aerial blight during the winter
months. Rooted plants from runners of Nephrolepis exaltata 'Fluffy Ruffle'
were obtained from commercial producers and planted in 4 inch pots
containing one of the following potting media: Canadian peat-sand (1:1,
v/v), Canadian peat-pine bark (1:1, v/v), and Canadian peat-vermiculite-
perlite (2:1:1, v/v/v). Each medium was steam-treated for 1.5 hours at
190*F prior to additions of 7 lb dolomite, 10 lb Osmocote 19:6:12, and 1.0
lb MicroMax (micronutrient source) per cubic yard. Factorial experiments
were used with the three potting media and three potting medium
temperatures (65-70, 70-75, or 75-85"F) with 10 plants in each treatment
inoculated with R. solani and 10 others treated with water alone. Potting
medium temperature was maintained with heated water in pipes under skirted
1This research was supported in part through a grant from the Florida
Associate Professor of Plant Pathology and Professor of Ornamental
Horticulture and Center Director, respectively, Agricultural Research and
Education Center, 2807 Binion Road, Apopka, FL 32703.
Inoculum of R. solani was prepared on potato-dextrose agar (PDA)
medium which was ground for 15 seconds in a Waring blender with tap water
and 10 ml of the resulting mycelial slurry added to the potting medium
surface in each pot. Plants were inoculated one week after placing on
temperature control benches. They were rated for percentage infection with
R. solani after 4 weeks. This test was performed once during the winter of
T984-1985 and once during the winter of 1985-1986.
Experiment 2. The second experiment evaluated effects of the same three
potting media and two other potting medium temperatures on Rhizoctonia
aerial blight during the summer months. Potting medium temperatures were
maintained by inserting pots into temperature control +chambers (2) with
ambient temperatures of 80 or 90*F controlled within 1"F. Air
temperatures in the greenhouse ranged from 75"F to 100F. Eight plants
each were used for the resulting six treatments. Other methods for this
experiment were the same as those described for Experiment 1 except that
all plants were inoculated with R. solani. This experiment was performed
twice during the summer of 1984.
Experiment 3. The third test evaluated the same factors as Experiment 2
with the exception that an air temperature factor was added. In this case,
the factorial design included the three potting media and two potting
medium temperatures used in Experiment 2 and two maximum air temperatures
of 95*F and 100*F. Methods used for this experiment were otherwise as
described for Experiment 2. This experiment was performed once during the
summer of 1984 and twice during the summer of 1985.
Experiment 4. The effect of various temperatures on in vitro growth of
five isolates of R. solani from foliage plants was evaluated in a single
test. Inoculum of each fungal isolate was grown on a PDA plate at
approximately 79"F for 4 days prior to use. Five plates of each fungal
isolate were incubated at each of the following temperatures: 41, 50,
59", 680, 77, 86, and 900F. Radial growth was measured at 24 hours.
Experiment 1. In the first experiment, disease severity was unaffected by
the potting medium used (Table 1). Disease severity increased as potting
medium temperature decreased in both tests. Although overall disease
severity was not great during these winter tests, it was significant and
caused complete loss of some plants in each test.
Experiments 2 and 3. In the second and third experiments, medium
composition again had no effect on severity of aerial blight of Boston fern
(Table 2). In contrast, potting medium temperatures of 90*F reduced
disease severity over medium temperatures of 80F in 2 of 3 tests
(Table 2). Finally, air temperatures affected disease severity in two of
three tests for experiment 2 (Table 2).
Experiment 4. The five isolates of Rhizoctonia from ornamentals responded
to temperature similarly with optimal growth at 86*F and significant
reductions in growth when maintained at 95F (Table 3).
In vitro response of Rhizoctonia to temperatures supports the
conclusion that differences in severity of disease based on either potting
medium or air temperature are at least partially due to direct temperature
inhibition of the pathogen. Increasing either potting medium or air
temperatures may not be a feasible means for controlling Rhizoctonia aerial
on Boston fern since the expense of heating potting media and air during
the winter can be high. Disease severity in Florida would be expected to
peak during periods when air temperatures are naturally within the range of
75* to 95"F with temperatures above 95"F resulting in reductions of disease
1. Chase, A. R., and R. T. Poole. 1984. Development of Myrothecium
leaf spot of Dieffenbachia maculata 'Perfection' at various
temperatures. Plant Disease 68:488-490.
2. Koller, C. D., L. K. Hiller, and R. W. Van Denburgh. 1980. A
forced-air system for controlling soil temperatures in plastic
pots. HortScience 15(2):189-190.
Table 1. Effect of potting medium temperature and potting
medium on severity of aerial blight of Boston fern caused
by Rhizoctonia solani during the winter (Experiment 1).
Treatment 1984-1985 1985-1986
Media Test 1 Test 2
Canadian peat-sand 9.0nsa 5.5ns
Canadian peat-bark 4.3 2.8
Canadian peat-vermiculite- 4.0 4.0
75 to 85"F 0.4 0.6
70 to 75"F 6.4 5.5
65 to 700F 10.4 8.6
Control 1.5 0.1
Rhizoctonia 10.0 14.1
aSignificance was denoted as follows: ns = not significant,
and ** P=0.01.
Table 2. Effect of potting medium temperature, air temperature and potting
medium on severity of aerial blight of Boston fern (Nephrolepis
exaltata) caused by Rhizoctonia solani (Experiments 2 and 3).
Percent foliage (crown) infection
Experiment 2 Experiment 3
Test Test Test Test Test
Factor 1 2 1 2 3
Canadian peat-sand 11.Onsa 10.6ns 0.3ns 7.0ns 27.3**
Canadian peat-pine bark 9.9 13.3 0.1 9.6 21.5
Canadian peat- 11.7 9.9 0.8 7.1 39.3
Potting medium temperature
80 F 13.7* 24.1** 0.2ns 12.0** 42.9**
90F 8.0 2.9 0.4 4.5 16.9
95F ---- ---- 0.6ns 13.1** 32.7**
105F ---- ---- 0.1 3.8 25.6
aSignificance was denoted
as ns = nonsignificant, P = 0.05, and ** P =
Table 3. In vitro growth of five isolates of Rhizoctonia solani from
ornamentals after 24 hours at different temperatures.- (Experiment 4).
Original host 41 50 59 68 77 86 95
Asplenium nidus 5.0a 7.0 10.6 16.8 39.4 46.4 18.4
Epipremnum aureum 5.0 5.0 13.2 13.6 30.8 39.0 13.2
Nephrolepis exaltata 5.0 5.0 10.6 12.8 28.6 33.8 10.0
Philodendron scandens 5.0 5.0 9.4 11.6 25.4 32.4 15.2
Rumohra adiantiformisD 5.0 6.8 17.0 21.6 37.0 39.8 7.2
aMean diameter (mm) for 5 replicates after 24 hours at a given temperature.
blsolate used for tests reported in this paper.