Septoria and Stagonospora Diseases of Cereals - CIMMYT ...

Session 5 — C.A. Cordo, M.R. Simón, A.E. Perelló, and H.E. Alippi
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Sampling date
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Figure 2. Weekly mean rainfall (a), weekly mean temperature (b), and weekly mean relative
humidity (c).
related to the end of the crop
vegetative period and the advent of
saprophytic pathogens on the
wheat debris. A new increase in
pycnidiospores on 5 March was
related to the first natural infection
of seedlings by septoria leaf blotch.
The pycnidiospore pattern in
petroleum jelly was constant from
the first week of observation
(Figure 1b). The increased density
was associated with the amount of
rain water. The correlation
A
27/3/99
B
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C
27/3/99
coefficient and the partial
regression coefficient between
pycnidiospores and rainfall were
significant (Table 1), as was the
regression coefficient for rainfall in
the multiple regression model. This
model explained 18% of the
variance (Table 2). Temperature and
humidity during this period were
probably not so high as to affect the
number of pycnidiospores released.
Similar to observations by Arseniuk
and Góral (1998), we recorded high
Table 1. Correlation coefficients and partial
correlation coefficients between number of
pycnidiospores in rain water and petroleum
jelly and number of ascospores of Septoria
tritici and Mycosphaerella graminicola with
weather variables.
Temp- Relative
erature humidity Rainfall
Pycnidiospores/
rain water -0.20 ns a 0.06 ns 0.26 ns
-0.19 ns b 0.04 ns 0.04 ns
Pycnidiospores/
p. jelly 0.12 ns 0.11 ns 0.53**
0.27 ns 0.01 ns 0.46*
Ascospores 0.53** 0.46* 0.57**
0.62** 0.42* 0.60**
a= correlation coefficient.
b= partial correlation coefficient.
Table 2. Multiple regression model of
weather variables and number of
pycnidiospores in rain water, petroleum jelly,
and ascospores of Septoria tritici and
Mycosphaerella graminicola.
Significance
Coefficient level
No. of pycnidiospores
in water
Constant 9.33
Temperature -0.26 ns
Relative humidity -0.01 ns
Rainfall
No. of pycnidiospores
in p. jelly
0.02 ns
Constant 11.31 ns
Temperature 0.20 ns
Relative humidity 0.07 ns
Rainfall
No. of ascospores
0.08 P