ISSN 1021-4437, Russian Journal of Plant Physiology, 2009, Vol. 56, No. 3, pp. 389–393. © Pleiades Publishing, Ltd., 2009.
Original Russian Text © T.S. Romanova, A.A. Aver’yanov, T.D. Pasechnik, V.P. Lapikova, C.J. Baker, 2009, published in Fiziologiya Rastenii, 2009, Vol. 56, No. 3, pp. 431–
It is known that ﬁne moisture ﬁlm, or droplets of
dew, or rain on plant shoots are prerequisites of pene-
tration of most phytopathogenic microbes. Therefore,
high humidity favors infective diseases as a rule . For
example, high rainfall increases severity of potato late
blight, apple scab, and grapevine downy mildew .
Rice blast infection caused by the fungus
requires drop water and relative humidity above 90%
that does not allow droplets to dry out within 24 h .
It is not excluded, however, that plants adapted to
these unfavorable conditions and respond to them by
reactions reducing, at least partially, the increased risk
of infection. This may look as an induction of disease
resistance upon leaf contact to water.
In addition to natural humidiﬁcation of plant shoots,
they are often sprayed artiﬁcially with various formula-
tions based usually on water. Water component of for-
mulations might also cause its own effect, the same as
that of natural moisture.
It is known that the mechanisms of innate and
acquired disease resistance involve oxidative burst, the
overproduction of reactive oxygen species (ROS) .
In particular, this was many times shown for the case of
rice blast. For example, leaf generation of superoxide
radical ( ) increased in plants whose resistance was
induced by high temperature , tricyclazole , ftha-
lide, probenazol , or phenanthroline complex of
cobalt . Therefore, if water-induced resistance
exists, its mechanism may involve superoxide radical.
The objective of this work was to elucidate the effect
of preinoculation contact of the rice leaf surface with
water droplets on visual symptoms caused by the sub-
sequent inoculation with the virulent
well as on production of leaves of cultivars differ-
ing in their resistance.
MATERIALS AND METHODS
Rice plants (
), Zenith (
, Aishi asahi (
), and Fukunishiki (
) were studied.
Rice Resistance to Blast Caused by Leaf Surface Moistening
Prior to Inoculation
T. S. Romanova
, A. A. Aver’yanov
, T. D. Pasechnik
, V. P. Lapikova
, and C. J. Baker
Research Institute of Phytopathology, Russian Academy of Agricultural Sciences, Bolshie Vyazemy,
Moscow oblast,143050 Russia;
fax: 7 (4986) 94-1124; e-mail: email@example.com
Molecular Plant Pathology Laboratory, Agriculture Research Service, United States Department of Agriculture,
Beltsville, Maryland, USA
Received April 15, 2008
—Effect of water droplets placed onto rice (
L.) leaves before inoculation with blast fun-
(Hebert) Barr on disease severity and superoxide radical generation by the leaves was
investigated. The leaves were inoculated by placement of spore suspension droplets. One day before, droplets
of distilled water were placed to the same sites as an inoculum. It was found, that such a pretreatment decreased
frequency of susceptible-type lesions by 2 to 2.5 times and increased that of symptomless outcome by 1.5 times
in comparison with the nontreated control. Besides, the pretreatment enhanced superoxide radical generation
in diffusates of healthy leaves of susceptible cultivar and in diffusates of infected leaves of resistant cultivar one
day post inoculation. It is suggested that water contacting with the leaf surface for a rather long time washes
out from its cells compounds possessing properties of plant endogenous elicitors. The latter induce superoxide
radical formation by plants and, as a consequence, their disease resistance. This may be interpreted as plant
adaptation to high humidity, which usually favors infections.
Key words: Oryza sativa - Magnaporthe grisea - acquired disease resistance - blast disease of rice - elicitors -
reactive oxygen species - superoxide radical - water metabolism
—superoxide anion radical; ROS—reactive
oxygen species; SOD—superoxide dismutase.