© Benaki Phytopathological Institute
Hellenic Plant Protection Journal
11:
47-53, 2018
DOI 10.2478/hppj-2018-0006
Department of Molecular Biology and Biotechnology,
AECS, P.O. Box 6091 Damascus, Syrian Arab Republic.
* Corresponding author:
Survival and germinability of
Rhynchosporium secalis
conidia
exposed to solar radiation
E. Al-Shehadah, A. Al-Daoude and M. Jawhar*
Summary
Rhynchosporium secalis
, the causal agent of barley scald disease, is a fungus com-
monly found in the environment. Disease spread within a field and between fields occurs through the
aerial dispersal of the fungal spores. However, not much is known about the survival potential of fun-
gal conidia exposed to solar radiation. In the present study, detached conidia of
R. secalis
were ex-
posed simultaneously in the field to direct sunlight or placed in an adjacent ventilated enclosure in
the dark for periods ranging from 0.5 to 8h. In addition, conidia were either exposed or not exposed
to UV-C light (254 nm) for periods ranging between 0.5 and 60 min in the laboratory. After exposure,
conidia were placed on water agar Petri dishes and allowed to germinate for 24h. Germinability of
conidia was reduced by up to 94% after 8h of exposure to solar irradiance (670-860 Wm
-2
) in the field in
comparison to the non-exposed control. Germinability of conidia in the laboratory was reduced up to
~100% by doses of UV-C light of 3.2±0.7 Wm
-2
. The results of this study will contribute to a better un-
derstanding of the relationship between climatic conditions and barley scald epidemics.
Additional keywords
: barley scald
,
climate, spore survival, UV-C light, virulence
due to the arrival of more aggressive iso-
lates of the pathogen underscores the need
for renewed and improved management of
the disease. Clearly, forecasts could be im-
proved if they included knowledge of the
presence or absence of the pathogen in an
area.
Not much is known whether
R. seca-
lis
conidia could be transported to a field
from an outside source, and, if transported,
whether they would initiate disease. Sever-
al researchers have determined the poten-
tial of
R. secalis
for
in vitro
spore production
(Stedman,
1980
; Avrova and Knogge, 2012).
However, to our knowledge, there have
been no published studies related to the es-
cape of
R. secalis
conidia in the air and their
capacity to survive exposure to direct sun-
lightand incite disease.
The purpose of the present work was to
investigate the survival potential of
R. seca-
lis
conidia exposed to solar radiation in the
field, as measured by their ability to germi-
nate after exposure to direct sunlight for
various lengths of time. The effect of UV-C
light on the germinability of
R. secalis
conid-
ia under controlled conditions was also eval-
uated.
Introduction
Aerial dispersal of inoculum is considered
an important factor in the epidemiology
of many fungal plant diseases (Aylor, 2003;
Stanosz
et al.,
2016).
Rhynchosporium secalis
(Oudem) J. J. Davis, the causal agent of scald
disease, is an important pathogen of barley
(
Hordeum vulgare
L.) worldwide (Zhan
et al.,
2008).
R. secalis
is considered economically
important because it can cause marked re-
duction in crop yield and quality (Yahyaoui,
2003). The appearance of scald disease in a
field with no previous history of barley crop-
ping can be attributed either to the use of
infected seed or to the transportation of air-
borne putative ascospores from sources out-
side the field. Once infection is established
in a crop, conidia and ⁄or putative ascospores
can then be easily dispersed throughout the
crop by rain splashing or wind (Fountaine
et
al.,
2010). Therefore, the recent resurgence
of the scald in new barley cultivation areas
