Title: Effect of growth medium on leaf and crown rot of liriope
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Title: Effect of growth medium on leaf and crown rot of liriope
Physical Description: Book
Language: English
Creator: Strandberg, James O.
Publisher: Institute of Food and Agricultural Sciences, University of Florida
Place of Publication: Gainesville, Fla.
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Bibliographic ID: UF00093683
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
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UNIVERSITY OF FLORIDA
INSTITUTE OF FOOD AND AGRICULTURAL SCIENCES
Mid Florida Research and Education Center
Apopka, Florida


EFFECT OF GROWTH MEDIUM ON LEAF AND CROWN ROT OF
LIRIOPE


James O. Strandberg


Plant Pathology Research Report 2002 3E March 2002


SUMMARY: Liriope bibs were propagated from a population of diseased 'Evergreen
Giant' plants and transplanted into 1-gallon pots containing several types and mixtures
of growth media. Significant levels of leaf and crown rot caused by Phytophthora
palmivora developed in these pots. In one experiment using artificially-inoculated plants,
there were differences in the levels of disease among the treatments. Builders' sand
had the lowest level of leaf and crown rot. In the second experiment, using a larger
number of naturally-infected plants, there were no significant differences in the
incidence or severity of leaf and crown rot between any of the growth media treatments.

INTRODUCTION: The purpose of this test was to evaluate the effect of growth media
on the incidence and damage by Phytophthora palmivora to Liriope muscari cv
'Evergreen Giant'. Preliminary work and observations in nurseries had indicated that
the growth medium might have a significant effect on infection by Phytophthora
palmivora and the development of the leaf and crown rot disease.


METHODS:

Experiment 1. Bibs of Liriope cv 'Evergreen Giant' were obtained from nursery-grown
plants that were not severely damaged by the leaf and crown rot disease as follows:
Plants were separated and leaves and roots were trimmed as in commercial
propagation. Before transplanting, the roots were dipped in a suspension of zoospores
of P. palmivora. Zoospores were prepared by flooding 5-day-old V-8 plates of P.
palmivora for 15 min at 4 C. Zoospores were suspended in 100 ml/plate of de-ionized
water. Roots of Liriope bibs were dipped just prior to transplanting into 1-gallon plastic
pots containing growth media comprised of various mixtures of pine bark, ground peat,
composted hardwood bark, and builder's sand as specified in Table 1. There were ten
plants in each treatment. Plants were placed within a shade structure covered with 70%


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shade fabric and watered with overhead sprinkler irrigation as needed. Each pot was
fertilized with 6g/pot of Osmocote 14-14-14 fertilizer. Bibs were transplanted on April 3
and plants were evaluated on July 2, 2001.


Experiment 2. This experiment was similar to Experiment 1, but differed in some
important aspects. Bibs of Liriope cv 'Evergreen Giant' were obtained from 3-gallon pots
of nursery-grown plants that, as a group, were severely damaged by the leaf and crown
rot disease. However, the obviously-diseased plants were discarded and were not
propagated. As the bibs originated from containers that already contained diseased
plants, they were likely to be infected or contaminated, so inoculation was not needed.
The bibs were transplanted on December 12, 2001 into 1-gallon plastic pots containing
various mixtures of pine bark, ground peat, composted hardwood bark, and builder's
sand as listed in Table 2. The plants were placed outdoors within a shade structure
covered with 70% shade fabric and watered with overhead sprinkler irrigation as
needed. Each pot was fertilized with 6g/pot of Osmocote 14-14-14 fertilizer. The plants
received freeze protection from overhead sprinklers on two nights and were not
damaged by low temperatures. Ten plants were closely grouped together for each
replicate. There were four replicates per treatment arranged in a complete block design.
Plants were evaluated for leaf and crown rot symptoms at 63, 75, and 90 days after
transplanting. At 90 days after transplanting, only small numbers of additional plants
were infected, so the experiment was terminated.


RESULTS AND DISCUSSION

Experiment 1. In this experiment, only 10 plants per treatment were used and the
plants were artificially inoculated with P. palmivora zoospores. Builders' sand had no
diseased plants and this value was significantly different than the other treatments
(Table 1). Although this result indicated that builders' sand was less conducive to leaf
and crown rot than other the growth media which contained peat or composted
hardwood bark, the results were not easy to interpret because of the small number of
plants and the experimental design. Moreover, the inoculation methods were
questionable. Either they were not very effective or the experiment was complicated by
the presence naturally-infected plants, because many of the uninoculated control plants
also became diseased. This indicated that some of the nursery-grown bibs were already
infected or contaminated with P. palmivora. Regardless, the absence of diseased
plants in the builder's sand treatment indicated that this medium suppressed disease
infection, development, or both.

Experiment 2. When sufficiently large numbers of naturally-infected (or contaminated)
bibs, obtained from pots containing diseased plants were used, results indicated that
there were no significant differences in disease development among the growth media
treatments (Table 2). Builders' sand and growth media containing 30% sand appeared
to be least conducive to disease development, as in experiment 1, but these values


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were not significantly different from those for other treatments (Table 2). However, the
results indicate that there might be a moderate effect of growth medium on disease
development and that some media are more conducive to disease development than
others. This result might be useful in a developing a disease management program for
leaf and crown rot. Further work will be required to more clearly elucidate the effects of
growth medium on the development of leaf and crown rot of Liriope. The effects of
growth media, if they exist, appear to be moderate, but even moderate suppression of
infection or disease development could be useful in a disease management program.




Table 1. Effect of growth medium on leaf and crown rot development in "Evergreen
Giant' Liriope plants at 90 days after transplanting. Summer, 2001.

Growth medium or components Ratio Percent
infected plants
90 days DAT1

Nursery mix (peat- pine bark- sand 30 : 40 : 30 14.0 b
Un-inoculated Control

Builder's sand 100% 0.0 a
(Inoculated)

Nursery mix + Composted hardwood bark 15.0 b
(Inoculated) 30: 40: 30

Nursery mix + Composted hardwood bark 10% 13.0 b
(Inoculated) 90 %

Nursery mix + Composted hardwood bark 20 % 2.0 b
(Inoculated) 80 %

Builder's sand + Composted hardwood bark 30 % 8.0 b
(Inoculated) 70 %

Fafard 3B Mix 45% peat 4.0 b
Peat, pine bark, vermiculite, and perlite

F = 2.563
P =0.028

1Average for ten pots evaluated at 90 days after transplanting. One-way ANOVA.
Values followed by the same letter are not significantly different. Student-Newman-
Keuls method where P <= 0.05.


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Table 2. Effect of growth medium on leaf and crown rot development in "Evergreen
Giant' Liriope plants. Winter 2001-2002.

Growth medium or Ratio Percent infected plants1
components at days after transplanting
63 75 90

Nursery mix = 25.0 32.5 32.5
peat pine bark sand 30 : 40 : 30

Builder's sand 100% 20.0 30.0 30.0

Nursery mix + Composted 50 % 30.0 35.0 40.0
hardwood bark 50 %

Nursery mix + Composted 30 % 22.5 37.5 37.5
hardwood bark 70 %

Nursery mix + Composted 10 % 20.0 37.5 37.5
hardwood bark 90 %

Builder's sand + Composted 50 % 32.5 42.5 47.5
hardwood bark 50 %

Nursery mix + Composted 30 % 45.0 50.0 50.0
hardwood bark 70 %

Fafard 3B Mix. Peat, pine 100% 20.0 42.5 42.5
bark, vermiculite, and perlite
F value 1.611 0.627 0.580
P= 0.180 0.729 0.765

1Average for ten pots per replicate and 4 replicates per treatment in a randomized
complete block design. None of the values are significantly different P = 0.05 level.


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