Research Highlights of the CIMMYT Wheat Program 1999-2000

Inquilab 91 and PBW343 showed unacceptably low
levels of adult plant resistance in Mexico when
tested with a race virulent to the above genes.
Similarly, a number of Kauz-derived varieties, e.g.
Bakhtawar 94 (Pakistan), WH542 (India), Memof
(Syria), Basribey 95 and Seyhan 95 (Turkey), and
Atrak (Iran), were released following widespread
epidemics in those countries on cultivars derived
from Veery#5. The immunity of Kauz in these
countries is due to the combination of Yr9 and
Yr27. Combined virulences for these two genes in
the yellow rust population does not exist at present
in the above countries; however, they are known to
occur in Mexico. Slow rusting gene Yr18, also
present in Kauz, does not by itself confer enough
protection under high disease pressure (Ma and
Singh, 1996 1 ); hence Kauz shows unacceptable
disease levels when tested in Mexico.
This type of information on the genetic basis of
resistance would be extremely useful for a country
preparing for a potential epidemic and trying to
diversify the crop by promoting genetically diverse
cultivars.
CIMMYT’s External Program and Management
Review panel in 1997 made a strong
recommendation to the Wheat Program to
reinitiate monitoring of changes in virulence of the
rust pathogens. This could have avoided the largescale
epidemic of yellow rust that occurred
recently. This recommendation was later endorsed
by the Technical Advisory Committee of the
CGIAR.
Breeding for rust resistance at CIMMYT, which
began in the late 1960s and early 1970s, has moved
a long way away from the use of major, racespecific
genes and currently focuses on
combinations of minor, slow rusting genes that
impart durability of resistance. However, all
cultivars currently grown in developing countries
are not likely to possess such resistance. Until a
majority of cultivars carry durable resistance, as is
the case for stem rust, monitoring the rust
pathogens and simultaneously evaluating the type
of resistance in the main cultivars are considered
essential for avoiding losses. Leaf and yellow rusts,
of high to moderate importance in all wheat
growing regions, will be the focal diseases. Stem
rust is currently considered important in Africa
and parts of the Southern Cone of South America.
In the 1980s CIMMYT established collaborative
arrangements with the Cereal Rust Laboratory, St.
Paul, Minnesota, and IPO, Wageningen, the
Netherlands, where samples of rusts for virulence
analysis could be sent from anywhere in the world.
However, such arrangements have no longer been
possible following the retirement of key scientists
in the above labs. After some discussion, the
decision was made at CIMMYT to promote the
establishment of Regional Monitoring Nurseries.
Epidemiological Regions for Monitoring
Nurseries
In developing countries wheat is grown in six
epidemiological regions that are not necessarily
fully isolated (Table 1). Though rusts can cross
boundaries between these regions, this may take
more time than moving within a given region,
where movement is less restricted. Eastern and
Southern Africa may well be separate regions;
however, due to the recent introduction of yellow
rust into South Africa and to increased human
migration between the two regions, the African
NARSs have decided to grow a common
monitoring nursery.
Table 1. The six regions participating in the monitoring of rust
pathogens.
Region
Indian Subcontinent
China
West Asia and North Africa 1
Eastern and Southern Africa
Central Asia
Southern Cone of South America
1
In collaboration with ICARDA.
Rusts
Leaf rust, yellow rust
Leaf rust, yellow rust
Leaf rust, yellow rust
Stem rust, leaf rust, yellow rust
Yellow rust, leaf rust
Leaf rust, yellow rust
1 Ma, H., and R.P. Singh. 1996. Contribution of adult plant resistance gene Yr18 in protecting wheat from yellow rust. Plant
Dis 80:66-69.
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