Septoria and Stagonospora Diseases of Cereals - CIMMYT ...

Session 6C — G. Shaner
130
Another approach to
determining progress in breeding
winter wheat for resistance to leaf
blotch is to examine cultivar
registrations in the journal Crop
Science over a period of years.
Registrations for 131 wheat
cultivars were published in
volumes 28-39, of which 96 were
for winter wheat. Of these winter
wheat cultivars, 25 were reported
to have some degree of resistance
to S. tritici or S. nodorum and 2 were
reported to be susceptible. For the
other 69 cultivars there was no
mention of reaction to either of
these pathogens. The summary for
winter wheat cultivars includes
both hard and soft, and red and
white classes, covering the eastern
portion of the US, the Great Plains,
and the Pacific Coast states.
Because leaf blotch has historically
been a greater problem in the
eastern region of the US, data were
summarized for this region. Of 39
wheat cultivars developed in the
eastern soft wheat region of the US,
15 were described as having some
resistance, none were described as
susceptible, and there was no
mention of reaction for 24 cultivars.
The absence of any comment about
reaction to leaf blotch is interesting,
because for many other wheat
pathogens and pests (e.g. rusts,
powdery mildew, viruses, Hessian
fly), the registration articles
commonly documented
susceptibility as well as resistance.
Of the 15 cultivars described as
being resistant, 12 were described
as having resistance to S. nodorum,
7 of which were described as
having resistance to S. tritici as
well. The other three cultivars were
described as being resistant only to
S. tritici.
An association has long been
noted between tall stature, late
maturity, and resistance to leaf
blotch caused by either S. tritici or
S. nodorum (Camacho-Casas et al.,
1995; Scott et al., 1982). Late
maturity and tall stature per se may
confer a significant degree of leaf
blotch in such cultivars. Where leaf
blotch is the greatest threat in
North America, the eastern soft
wheat region, breeders have
emphasized development of short
(90 to 100 cm), early maturing
cultivars, as a way to reduce risk
from rust infection, to permit grain
filling before the excessive hot and
humid conditions of summer, and
to permit double-cropping with
soybeans. The desired standards of
early maturity and short stature
may be an important reason for the
lack of progress in achieving
adequate levels of resistance to the
leaf blotch pathogens.
Hectares of soft wheat
production in the eastern US have
been declining for many years.
Poor yields and poor grain quality
because of disease have been a
major reason for the abandonment
of wheat production by many
farmers. Unless greater degrees of
resistance can be bred into highyielding,
early-maturing, shortstatured
wheat cultivars, this
downward trend in production will
likely continue.
References
Camacho-Casas, M.A., W.E.
Kronstad, and A.L. Scharen. 1995.
Septoria tritici resistance and
associations with agronomic traits
in a wheat cross. Crop Sci. 35:971-
976.
Patterson, F.L., Roberts, J.J., Finney,
R.E., Shaner, G.E., Gallun, R.L.,
and Ohm, H.W. 1975. Registration
of Oasis wheat. Crop Sci. 15:736-
737.
Patterson, F.L., Shaner, G.E., Huber,
D.M., Ohm, H.W., Finney, R.E.,
Gallun, R.L., and Roberts, J.J. 1979.
Registration of Sullivan wheat
Crop Sci. 19:297.
Scott, P.R., Benedikz, P.M., and Cox,
C.J. 1982. A genetic study of the
relationship between height, time
of ear emergence and resistance to
Septoria nodorum in wheat. Plant
Pathology 31:45-60.
Shaner, G., and Buechley, G. 1995.
Epidemiology of leaf blotch of soft
red winter wheat caused by
Septoria tritici and Stagonospora
nodorum. Plant Disease 79:928-938.