Septoria and Stagonospora Diseases of Cereals - CIMMYT ...

a moist chamber (wooden frame
covered with a polyethylene
sheet) for 72 hours. High
humidity (95% or above) was
maintained using a humidifier
(ultrasonic, cool mist type) inside
the moist chamber. The pots were
subsequently returned to a
greenhouse bench in a
randomized complete block
design.
Percent lesion area on the
second leaf from the base of each
of the 10 plants in each pot was
estimated visually at three weeks
after inoculation. Each of two
observers half of the plants in
each pot.
% diseased leaf area
% diseased leaf area
90
80
70
60
50
40
30
20
10
0
90
80
70
60
50
40
30
20
10
0
6-Feb
6-Feb
Madsen (MR)
Stephens (S)
Mixture
27-Feb
20-Mar
Madsen (MR)
W-301 (S)
Mixture
27-Feb
20-Mar
10-Apr
10-Apr
Effects of pathogen diversity
on epidemic progression
A field experiment that allowed
us to examine the influence of
pathogen diversity on epidemic
increase in variety mixtures was
conducted in the 1994-95 season.
These plots were treated in a
manner highly similar to those
described above, and have been
discussed in more detail elsewhere
(Zhan et al., 1998). Treatments were
a complete factorial of three host
treatments (pure stand of Madsen,
pure stand of Stephens, and a 1:1
mixture of Madsen:Stephens) and
two inoculation treatments (natural
and artificial) in a completely
random design with three
replications. One set of plots was
naturally inoculated, while the
1-May
1-May
22-May
22-May
12-Jun
12-Jun
% diseased leaf area
% diseased leaf area
90
80
70
60
50
40
30
20
10
0
90
80
70
60
50
40
30
20
10
0
6-Feb
6-Feb
Cashup (MR)
Stephens (S)
Mixture
27-Feb
20-Mar
Cashup (MR)
W-301 (S)
Mixture
27-Feb
20-Mar
Disease Management Using Varietal Mixtures 113
other was sprayed in November
1994 with a mixture of 10 isolates to
competitively exclude the highly
diverse inoculum provided by
outside ascospore showers.
Results
The Madsen/Stephens and
Cashup/Stephens mixtures
suppressed epidemic development
below that of the more resistant
component in each mixture (Figure
1). In contrast, the mixtures
containing the variety W-301 as the
susceptible component performed
less well, with the Cashup/W-301
mixture showing no epidemic
suppression relative to the mean of
the component pure stands
(Figure 1).
Figure 1. Disease progress of septoria tritici blotch in naturally-occurring epidemics of pure stand varieties
and 1:1 variety mixtures. MR = moderately resistant and S = susceptible.
10-Apr
10-Apr
1-May
1-May
22-May
22-May
12-Jun
12-Jun