Septoria and Stagonospora Diseases of Cereals - CIMMYT ...

targeted for S. tritici-prone regions
is exposed to the disease 3-4 times
during the segregating phase when
grown in Toluca. During the
selection process, selection
intensity is increased as the
segregating populations are
advanced. At the end of the shuttle
breeding process, all homozygous
lines are exposed for two
additional cycles at three sites in
the high rainfall Mexican
highlands: Toluca, Patzcuaro
(Gomez and Gonzalez, 1987), and
El Tigre.
Shuttle breeding is followed by
multilocation testing at key
locations around the world through
a network of cooperators. The
global data allow truly outstanding
material (see Gilchrist et al., these
proceedings) to be identified and
used as new parents in the ongoing
process of recombining genetically
different sources of resistance, and
they also offer the prospect of
combining different resistance
mechanisms.
Future work will concentrate on
combining accumulated resistances
that are based on different genes
and/or different resistance
mechanisms, with superior yield,
scab resistance, shattering
tolerance, and industrial quality.
Conclusions
Several conclusions in regard to
the impact of our increased
understanding of resistance on
related breeding aspects can be
drawn from the combined research
of the past decade:
1. There are many sources of genetic
resistance available that have
either been shown to be different
or seem to behave differently.
Many of those resistances have
proven to be quite stable.
2. Seedling data at best are an
indication of adult plant
resistance, and testing adult
plants in a field situation appears
crucial.
3. A variety is rarely replaced
solely or primarily because it
succumbs to one of the
septoria/stagonospora blights.
4. The relative role of virulence and
aggressiveness in the field may
soon be elucidated using
molecular tools in combination
with the ability to cross among
isolates. The outcome should
have direct impact on breeding
strategy.
5. The diversity of isolates at the
field level makes gaining a
deeper understanding of
interactions among these isolates
of paramount importance. The
breeder needs to take this into
consideration when planning to
artificially inoculate, or rely on
multisite testing.
6. Multilocation confirmation of
advanced lines remains a
necessity, while the debate on
possible specificity continues.
Breeding for Resistance to the Septoria/Stagonospora Blights of Wheat 123
While several of these exciting
issues remain in debate, advances
in breeding for resistance to the
septoria/stagonospora pathogens
have not ceased. Breeders have
continued to produce varieties with
higher yields, better industrial
quality, and improved resistance to
multiple diseases.
References
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