American Journal of Plant Sciences, 2011, 2, 50-51
doi:10.4236/ajps.2011.21006 Published Online March 2011 (http://www.SciRP.org/journal/ajps)
Seedling Blight of Festuca arizonica Caused by
Rhizoctonia solani
Mopuri N. Reddy1, Stanley H. Faeth2
1Department of Applied Microbiology, S P Mahila Visvavidyalayam, Tirupati, India, 2Department of Biology, University of North
Carolina at Greensboro, Greensboro, USA.
Received August 12th, 2010; revised October 28th, 2010; accepted November 3rd, 2010.
ABSTRACT
We report here a damping-off disease occurring at the seedling stage of the grass Festuca arizonica (Arizona fescue)
that is caused by the soil-borne fungal pathogen Rhizoctonia solani.
Keywords: Damping-off, Endophytes, Festuca Arizonica, Rhizoc tonia Solani
1. Introduction
Festuca arizonica (Vasey) or Arizona fescue (Pooideae)
is a perennial bunch grass native to Arizona, Nevada,
New Mexico and Colorado in the U S A and in Northern
Mexico [1]. Arizona fescue grows in semi-arid grass-
lands at the elevations between 2300 m and 3200 m. It
has been studied extensively with regards to its associa-
tion with the asexual and systemic fungal endophyte
Neotyphodium and how the en dophyte alters host growth
and reproduction and resistance to herbivores and patho-
gens [2-4]. Although this native grass is important as
forage grass and in ecological studies, little is known
about the diseases o ccurring on this plant.
Rhizoctonia solani is one of the most common soil-
borne fungal pathogens, ubiquitous in nature and exhibits
a strong saprophytic ability, a high degree of pathogenic-
ity and a wide host range. R. solani can infect seeds,
seedlings or adult plants. When seeds are infected, they
may fail to germinate. If infected seeds germinate, then
the young seedlings may fall over at the soil line because
R .solani first infects the hypocotyls as the seedling
emerges to the surface of the soil or infects the stem at
the soil line.
Here, we report a damping-off disease occurring at the
seedling stage that is caused by the soil-borne fungal
pathogen Rhizoct onia solani.
2. The Disease
In experimental plots of Festuca arizonica some of the
seedlings were observed to show damping-off symptoms
about two weeks after emergence. Infected seedlings
occurred as scattered plants among apparently healthy
seedlings. Infected seedlings were lifted out carefully,
gently washed and observed for symptoms.
The hypocotyls of infected seedlings showed initial
water-soaked lesions which gradually turned dark
brown reddish brown and become sunken and dry, gir-
dling the hypocotyls at or near the surface of the soil and
ultimately resulting in the total collapse of the seedlings
(Figure 1). The seedlings gradually become chlorotic
and collapsed. On older seedlings, the rotting extended
downward, killing the tap root and lateral roots (Figure
2).
Repeated isolations and inoculation studies showed that
Figure 1. Arizona fescue seedlings showing water-soaked
symptoms on hypocotyls at initial stages of infection.

Seedling Bli ght of Festuca arizonica Caused by Rhizoctonia solani 51
Figure 2. Characteristic dar k brown, sunken le sions at later
stages of infection on the hypocotyls, including rotting of
the tap root and root laterals and the collapse of the seed-
lings.
Rhizoctonia solani Kuehn was primarily responsible for
the disease. Pathogenicity of the isolate was proved by
following the Koch’s Postulates. The pathogen was
grown on 3% oatmeal-sand medium in 250 ml Erlen-
meyer flasks for 10 days. The inoculum was thoroughly
mixed with the top 5 cm of soil in po ts in th e green house.
Healthy 10 day old F. arizonica seedlings were trans-
ferred to the pots and observed periodically for disease
occurrence. Some of the pots contained Neotyphodium-
infected seedlings while others contained endophyte-free
seedlings. Typical disease symptoms on healthy seed-
lings appeared 5 days after inoculation. The total matu-
ration of lesions and collapse of the seedlings occurred
about three weeks after inoculation. The disease occur-
rence and seedling loss was greater for seedlings of grass
genotypes without endophyte infection than those in-
fected by Neotyphodium. This suggests that endophyte
infection may suppress R. solani infection or disease in-
tensity. Because the effects of endophytic infection on
the seedling diseases are not well-studied [3], R. solani
may be a good candidate for studies that test how endo-
phyte infection alters pathogen resistance in Arizona
fescue.
The culture was maintained on PDA with periodical
transfers. The fungus produced cottony mycelial growth,
with brown to dark brown round to irregular sclerotia on
the medium. The identity o f the pathogen as Rhizoctonia
solani Kuehn was via standard morphological and cul-
tural characteristics as suggested by Parmeter [5] by
comparison with to a R. solani reference culture. Cultur-
ing surface sterilized seeds of F. arizonica on water agar
and on Rhizoctonia specific medium showed growth of
the fungus from the seeds. Thus, R. solani may be seed-
borne and may be transmitted vertically to seedlings,
similar to Neotyphodium endophytes, in addition to hori-
zontal transmission to seed lings in the soil.
A search of the literature to d ate in Biolo g ical Reviews,
Phytopathology, USDA Hand Books, and Rhizoctonia
specific monographs and reviews revealed no reports of
occurrence of damping-off caused by Rhizoctonia solani
on F. arizonica. Therefore, this paper may be considered
as the first report of this fungal disease on F. arizonica.
3. Acknowledgements
The authors are indebted to Sally Wittlinger for techn ical
assistance. Support was provided by the School of Life
Sciences, Arizona State University, Tempe USA to Prof.
M. N. Reddy, as Visiting Professor and by NSF Grants
DEB 0613551 and 091774 1 to S.H.F.
REFERENCES
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