Meeting the Challenge of Yellow Rust in Cereal Crops - ICARDA

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the greenhouse. APR genes are investigated at the adult plant stage under field
conditions. The first differential system for physiological races of wheat yellow
rust was established in 1930 (Allison and Isenbeck, 1930). The present system
for identification of races, which is utilized in many parts of the world, was
proposed by Johnson and Taylor (1972). This system was modified by Wellings
and McIntosh (1990).
Until now, many resistance genes have been recognized, among them the
genes Yr11, Yr12, Yr13, Yr14, Yr16 and Yr18. They are APR genes. The first
study on virulence factors of wheat yellow rust was conducted in a trap
nursery by Zadoks (1961). The seedling-resistance genes are naturally
expressed at all growth stages, and thus can be surveyed in field condition (in
trap nurseries). Besides seedling-resistance genes, APR genes can be expressed
as well. In order to monitor annual changes in races and virulence factors of
wheat yellow rust, national experiments have been carried out since 1993 in
Iran. In some of these studies, virulence factors of pathogen have been
distinguished, and effective resistance genes have also been recognized. For
example, results of Nazari and associates showed that Ardabil races have
virulence for genes Yr9, Yr7, Yr8, Yr2, Yr6, YrSU, Yr19, Yr8, Yr17, Yr25, Yr23,
Yr22 and Yr10. In their study they also concluded that genes YrSP, Yr1, Yr3,
Yr49, Yr5, Yr16, Yr24, Yr13, Yr14, Yr15 and YrCV were effective genes (Nazari
et al., 2000).
Virulence on Yr1 and Yr17 has spread rapidly in central Asia. Virulence on
Yr1 was first observed in Tajikistan in 1999 and by 2004 it was found across
central and West Asia. Virulence on Yr10 and Yr17 was observed in Yemen in
1999, virulence on Yr18, 27 and 24 were recorded in 2002, and by 2005 these
virulence types were recovered at many locations in CWANA (Yahyaoui,
2006).
Comprehensive information on pathogen virulence and variation, and
epidemiological information on pathogen movements, provides a basis for the
development of early warning systems (Yahyaoui et al., 2001).
The objective of this study was to determine effective and ineffective
resistance genes to wheat yellow rust in the period 2006–2009.
Material and methods
In this investigation 192 different genotypes were used. The entries included
differential cultivars with seedling-resistance genes, cultivars with APR and
durable resistance genes, near-isogenic lines and promising lines. The entries
were sown in Ardabil agricultural research station under natural infection
conditions. Each entry was planted in two 1-m long rows 30 cm apart. Plots
were spaced at 65 cm. One susceptible cultivar (Bollani) was used after each 10
entries. The disease severity was estimated based on a modified Cobb scale