Septoria and Stagonospora Diseases of Cereals - CIMMYT ...

Breeding for Resistance to Septoria and
Stagonospora Blotches in Winter Wheat in
the United States
G. Shaner
Department of Botany and Plant Pathology, Purdue University,
West Lafayette, IN, USA
This report will concentrate on
resistance breeding efforts in the
winter wheat region of the United
States, where leaf blotch, caused by
either Septoria tritici or Stagonospora
nodorum, has been a chronic
disease. Leaf blotch has been a
recognized problem in the eastern
soft winter wheat region of the US
for more than 50 years. Historically,
Stagonospora nodorum was the major
pathogen in the southeastern US
and Septoria tritici was the major
pathogen in the north-central
regions. Since the mid 1980s,
however, S. nodorum has been at
least as damaging in the northcentral
region as S. tritici.
The Purdue University-USDA
small grain improvement program
provides an example of efforts to
manage leaf blotch by use of
genetic resistance. During the mid
1950s, wheat breeders began to
incorporate resistance to S. tritici
into adapted soft red winter wheat
cultivars. At that time, S. tritici was
clearly the dominant leaf blotch
pathogen. The primary sources of
resistance were wheat cultivars
from South America, e.g. Bulgaria
88, Sao Sepe, and Sudeste.
Eventually, most effort
concentrated on Bulgaria 88 as the
source of resistance. Cultivars
Oasis and Sullivan, released in 1973
and 1977, respectively, carried this
resistance (Patterson et al., 1975;
1979). When Oasis or Sullivan are
inoculated at the adult plant stage
in the greenhouse with spores of S.
tritici, they are highly resistant.
Infection results in small chlorotic
flecks, with little or no chlorosis
and no formation of pycnidia.
Resistance in these cultivars
segregates as a single, dominant
Mendelian factor when they are
crossed to a susceptible cultivar.
Although Oasis derived its
resistance to S. tritici mainly from
Bulgaria 88, it evidently carried
additional factors for resistance to
S. nodorum because it exhibited a
degree of resistance and performed
well in areas of the southeastern US
where this species was the
dominant leaf spotting pathogen.
This additional resistance may
have resulted from the fact that
selection for resistance in Indiana
was entirely in the field under
conditions of natural infection, and
there may have been more S.
nodorum present than was
suspected.
Since the latter half of the 1980s,
S. nodorum has emerged as the
dominant leaf spotting pathogen in
Indiana (Shaner and Buechley,
1995). This shift in pathogen
populations has evidently occurred
throughout the north central region
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of the US, and leaf blotch must now
be regarded as a complex involving
both S. tritici and S. nodorum. In
more southern regions, S. nodorum
continues to be the major leaf
spotting pathogen.
Management of this disease
complex by genetic resistance
requires resistance to both
pathogens. Despite at least 50 years
of effort in breeding for resistance
to leaf blotch, progress has been
modest. Evidence for this
conclusion comes from descriptions
of cultivars developed in this
region and from direct observation
of many cultivars in field trials.
An estimation of the degree of
resistance available in currently
available cultivars of soft red
winter wheat can be obtained from
data collected in statewide wheat
performance trials conducted each
year in Indiana. For many years,
entries in this trial have been
evaluated for disease. Leaf blotch is
encountered every year to some
degree in Indiana wheat fields, but
at varying severity. For the period
1973–91, leaf blotch symptoms
reached the flag leaf of susceptible
cultivars within 26 days of heading
in 10 of the 19 years (Shaner and
Buechley, 1995).