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SFort Pierce ARC Research Report RL-1977-1
Sj_ Two Additional Helminthosporium spp. on Bermudagrasses in South Florida
i/R. M. Sonoda./
Two new Helminthosporium-bermudagrass pathogen host relationships are reported.
Helminthosporium setariae caused heavy leaf-spotting on Coastcross #1 bermuda-
grass. H. hawaiiense was consistently isolated from heavily spotted leaves of
Leaf-spotting of several bermudagrasses, Cynodon spp., in a replicated
planting of 52 potential forage grasses was noticed in the summer of 1973 at
the Agricultural Research Center, Fort Pierce (ARC-FP). Disease symptoms were
similar to those described for several Helminthosporium spp. reported on Cynodon
dactylon (L.) Pers. in Florida (3). Studies on the disease were initiated
because of the severity of symptoms on a promising forage type, Coastcross #1, a
cross.between Coastal bermudagrass and bermudagrass P. I. 255445, released by the
Georgia Agricultural Experiment Station (1). Coastcross #1 is being grown on
several farms near the ARC-FP. In addition, fungi from a leaf-spotting disease
noticed in the winter of 1973-1974 on a stand of Coastal bermudagrass growing on
a ditchbank at the ARC-FP was isolated and identified.
Materials and Methods
There were four replicates each of Coastcross #1 (IRFL #153), C. sp. (IRFL
#555), C. nlemfuensis Vanderyst var. nlemfuensis Clayton and Harlan (IRFL #7),
and C. nlemfuensis var. robustus Clayton and Harlan (IRFL #514, IRFL #546 and IRFL
#5567, in a planting of 52 grasses. Each replicate consisted of a plot 6 feet
wide and 11 feet long. Plantings were made from the summer through the fall of
1972. Plots were harvested at 5 to 7-week intervals from September 1972 until
the middle of June 1973. Following the mid-June harvest, there was a 3-month
interval before the subsequent harvest.
Disease incidence ratings were made in mid-July and late August. The
ratings were made on the third fully expanded leaf of ten randomly selected
shoots in each plot. The rating scale used was 1= no leafspot; 2= 1-3 leafspots
per cm leaf length; 3= 4-7 leafspots per cm; 4= 8-15 leafspots per cm and 5=
16 or more leafspots per cm. Analysis of variance was run on the mean disease
ratings. Duncan's Multiple Range test was used to separate means. No rating for
l/ Associate Plant Pathologist, University of Florida, Institute of Food and
Agricultural Sciences, Agricultural Research Center, Fort Pierce.
JUN i22 977
disease incidence was made on the Coastal bermudagrew growing along the ditchbank,
an apparent escape from earlier field tests.
Single lesions (one mm2 leaf tissue), excised after immersing diseased leaves
in 0.5% NaOCI and 0.1% Triton X-100 for about one minute, were plated out on 2%
water agar. Morphological characteristics of spores produced on host tissue or on
agar near the tissue were used to identify the fungi using criteria in keys by
Ellis (2) and Luttrell (4).
Results and Discussion
Dark brown lesions from less than 1 mm to about 4 mm in length occurred on
plants in the replicated planting. There was an indistinct halo around most of
the lesions. Heavily infected leaves, especially those on Coastcross #1, turned
yellow, then straw-colored and dried up. Lesions on Coastal bermudagrass were
lighter, more reddish brown in color and surrounded by a distinct yellow-brown
Coastcross #1 had the heaviest incidence of leafspot in both ratings (Table
1). The predominant fungus on the Cynodon spp. was identified as Helminthosporium
setariae by Ellis' key (2). Spores of the fungus were 11.8 to 15.5 u by 54.8 to
99.2 i (avg. 12.5 x 75.0 i). Spores varied in color from a pale brown to dark
brown depending on the isolate. Other fungi obtained from lesions on the Cynodon
spp., in decreasing frequency, were H. stenospilum, Curvularia spp., H. cynodontis,
H. rostratum, H. hawailenee and save~ t. unidentified Helminthosporium spp. In
some cases, two or more species of fungi were obtained frQm the same lesion.
This, to the author's knowledge, is the first report of H. setariae vu wermuaa-
Coastcross #1 bermudagrass was reported to be highly resistant to leaf-
spotting diseases (1). The results presented here indicate that it can be
severely affected by Helminthosporium spp.
The predominant fungus obtained from lesions on the Coastal bermudagrass was
Helminthosporium hawaiiense. A few H. cynodontis, H. setariae, H. stenospilum
and Curvularia spp. were also obtained. H. hawaiiense was first reported from
the U. S. from the ARC-FP in 1973 (5). This, to the author's knowledge, is the
first report of H. hawaiiense on bermudagrass.
1. B:rton, G. W. 1962. Registration of varieties of bermudagrass. Crop Sci.
2. Ellis, M. B. 1971. Dematiaceous hyphomycetes. Commonwealth Mycological
Institute. Kew, Surrey, England. 608'pp.
3. Freeman, T. E. 1969. Diseases of southern turfgrasses. University of
Florida, IFAS, Agr. Exp. Sta., Tech. Bull. 713A. 31 pp.
4. Luttrell, E. S. 1951. A key to species of Helminthosporium reported on
grasses in the United States. Plant Disease Reporter Supplement 201:
5. Sonoda, R. M. 1974. Helminthosporium hawaiiense on Rhodesgrass in Florida.
Plant Disease Reporter 58:490.
Table- .. Ratinga-of leafspot incidence-on-eix-aecessions of Cynodon
app. in July and August, 1973.
Cynodon sp. Accession # July 17 August 28
nlemfuensis var. nlemfuensis 7 2.7 bec/ 2.7 h2/
Coastcross # 1 3/ 153 4.4 a 4.0 a
nlemfuensis var. robustus 514 2.5 c 2.2 b
nlemfuensis var. robustus 546 3.0 b 2.7 b
sp. 555 2.0 d 2.6 b
nlemfuensis var. robustus 556 2.9 be --
1/ Rating system: 1 = no leafspots; 2 = 1-3 leafspots per cm leaf length;
3 = 4-7 leafspots per cm; 4 = 8-15 leafspots per cm, and 5 = 16 or
more leafspots per cm.
2/ Means in the same column followed by the same letter are not
significantly different at the 5% level (Duncan's new multiple range
3/ A cross between Coastal bermudagrass and bermudagrass P. I. 255445.