Septoria and Stagonospora Diseases of Cereals - CIMMYT ...

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Spore Dispersal of Leaf Blotch Pathogens of Wheat
(Mycosphaerella graminicola and Septoria tritici)
C.A. Cordo, 1, 3 M.R. Simón, 2 A.E. Perelló, 1, 4 and H.E. Alippi1 1 Centro de Investigaciones de Fitopatología (CIDEFI), Facultad de Ciencias Agrarias y Forestales de La Plata,
La Plata, Argentina
2 Laboratorio de Cerealicultura, Facultad de Ciencias Agrarias y Forestales de La Plata, La Plata, Argentina
3 Comisión de Investigaciones Científicas (CIC), Provincia de Buenos Aires, Argentina
4 Consejo Nacional de Investigaciones Científicas y Tecnológicas (CONICET), Provincia de Buenos Aires,
Argentina
Abstract
The spatial and temporal patterns of discharge and dissemination of air-borne Mycosphaerella graminicola spores
and of Septoria tritici spores through rain splash were studied. Spore traps were used to monitor both ascospores and
pycnidiospores when the wheat crop was in the vegetative and debris states. Relationships between distance from a point
source and weather variables such as rainfall, relative humidity, and air temperature were analyzed. The release of
pycnidiospores was favored by rainfall, as was explained through the multiple regression model (18% of the variation). Air
dispersal of ascospores and splash dispersal of pycnidiospores were significantly influenced by each of the weather
variables. The number of air-borne ascospores increased in association with rainfall. The multiple regression model
explained 59% of the variation. The correlation analysis showed significant association with temperature, humidity, and
rainfall; the regression coefficients of the climatic variables were significant. The effect of different distances from the
inoculum source on the density of rain-splashed pycnidiospores and wind-borne ascospores was not significant.
Pycnidiospores were the omnipresent inoculum in the cereal-producing area during the observed period. Thus this
inoculum poses a risk to crop production and may be important to the epidemiology of septoria diseases under the climatic
conditions in the wheat-producing areas of Argentina.
Leaf blotch, caused by Septoria
tritici Rob.ex Desm. (teleomorph
Mycosphaerella graminicola (Fuckel)
Schroeter, in Cohn) is an important
wheat (Triticum aestivum) disease
that causes yield losses in different
regions of the world every year
(Shipton et al., 1971; Eyal, 1981;
Eyal et al., 1987). Its incidence
depends on cultivar susceptibility,
inoculum availability, crop
management practices, and
favorable environmental conditions
(cool temperature, high humidity,
and frequent rain). Climatic factors,
especially precipitation, affect
fungal growth and the amount and
timing of spore production, as well
as the release, dispersal, and
deposition of spores. Unusually
intense rain may cause the onset of
a S. tritici epidemic in a wheat crop.
The greatest risk to a crop is related
to the occurrence of conditions that
favor spore dispersal during and
shortly after flag leaf emergence.
Spore dispersal and infection at this
time favors a second generation of
pathogens. Spore dissemination
patterns of Phaeosphaeria spp. and
Stagonospora spp. have been
described (Arseniuk and Góral,
1998; Góral and Arseniuk, 1998;
1991). The release of M. graminicola
ascospores occurred at two peak
times of the year (at crop
emergence and emergence of the
upper two leaves) (T. Hunter
unpublished).
This work aimed at producing a
mathematical model of
pycnidiospore and ascospore
dispersal by:
1. determining the pattern of spore
dispersal during a 6-month
period;
2. investigating the effect of
climatic variables (rainfall,
temperature, humidity) on
density of air-borne spores; and
3. doing a preliminary analysis of
the dispersal distance for both
types of spores.
Materials and Methods
In the experiment station
situated in Los Hornos, near La
Plata, Buenos Aires Province, airborne
spores were collected on 13
spore traps made of PVC capsules
containing slides covered with
petroleum jelly. The capsules were
fixed to wooden stakes 0.7 m above
the soil surface. Glass tubes 0.03 m
in diameter and 0.16 m long were