Septoria and Stagonospora Diseases of Cereals - CIMMYT ...

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Selecting Wheat for Resistance to
Septoria/Stagonospora in Patzcuaro, Michoacan, Mexico
R.M. Gonzalez I., 1 S. Rajaram, 2 and M. van Ginkel2 1 Campo Morelia, National Livestock and Agricultural Research Institute, Mexico
2 CIMMYT Bread Wheat Program
Abstract
The research reported in this paper was conducted in the humid, temperate area of Patzcuaro in the state of Michoacan, in
Mexico, where there is a high natural incidence of Septoria/Stagonospora spp. Nine wheat genotypes that had previously been
selected for resistance to Septoria/Stagonospora spp. were included in the study. They were compared to two check varieties, one
tolerant and one susceptible. The materials were tested with and without chemical protection. Three years’ data were analyzed and
relative yield losses of 10-32% were found. Two different responses were observed among the outstanding genotypes. On the one
hand, several lines expressed little reduction in yield when challenged by the septoria pathogens. Depending on their yield potential,
final yield could be moderate to quite good. These could be classified as resistant or tolerant to Septoria/Stagonospora spp. Some of
these same materials did show a considerable level of severity; their response would thus be better classified as tolerance rather than
resistance. On the other hand, certain materials with high yield potential did lose yield following the attack by the septoria foliar
blights, but retained sufficient expression of yield potential to compete well with the local check variety. These should not be classified
as resistant nor tolerant, but may well be desirable from a production standpoint. The line that best combined these traits is IAS20/
H567.71/5*IAS 20. It is being considered for release under the name Patzcuaro. Severity of foliar disease on the flag leaf proved to be
well correlated with yield loss.
Over the past 15 years, Mexico’s
National Livestock and
Agricultural Research Institute
(INIFAP) and CIMMYT have
worked together on breeding bread
wheats for resistance to Septoria
tritici and Stagonospora nodorum in
the Patzcuaro, Michoacan, region of
Mexico. Natural conditions in this
area favor the yearly development
of these two Septoria species
(Gomez and Gonzalez, 1987). The
area enjoys a temperate climate,
with mean temperatures of 8-21ºC,
> 800 mm annual rainfall, and >
85% relative humidity. The isolates
of Septoria/Stagonospora spp. that
thrive under these conditions are
very aggressive, which makes this
a stress environment for wheat.
According to Eyal et al. (1985), the
Septoria isolates present in the
Patzcuaro area are among the most
virulent in the world.
Materials and Methods
In this study, 11 advanced
wheat lines from CIMMYT
nurseries (Table 1) targeted for high
rainfall production environments
(e.g., HRWSN and ASWSN) were
evaluated with and without
chemical protection during 1994-96.
The variety Curinda M-87,
which has functioned as reference
in our work for the past 10 years,
was used as the resistant/tolerant
check variety in the trials (Table 1).
The variety Batan was the
susceptible check. Although both S.
tritici and S. nodorum were present,
the former was found in a higher
proportion in most years.
Fungicides Terbuconazole and
Tecto were used for chemical
control. Terbuconazole was applied
every 10 days starting from
tillering to grain milk stage at a
dosage of 0.5 l/ha. Tecto was
applied in the same dosage every
eight days, starting at the end of
the booting stage.
Days to flowering, percentage
flag leaf area affected by Septoria/
Stagonospora spp. (% flag leaf
severity, FLS) at grain milk stage,
plant height, grain yield, and test
weight were measured. Yield losses
and correlations were calculated for
individual years.
Results and Discussion
Several lines expressed higher
levels of resistance than the
resistant check variety Curinda
(29% FLS) (Table 1). Severities as
low as 1-3% were noted in
individual years. Across the three