Meeting the Challenge of Yellow Rust in Cereal Crops - ICARDA

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Syria, Lebanon, Iran and Turkey. Race 6E0 is also virulent to YrA that is
present in many wheat cultivars that are still cultivated over relatively large
areas in Turkey, Lebanon and Syria. Race 38E150 was the second most
frequent race in Syria and was found in the last five consecutive years, whereas
134E146 and 38 E134 were identified in rust samples for four consecutive
years. These races originated from durum wheat leaf samples and most of
them were not detected in 1999. The frequency of P. striiformis virulence genes
was determined based on defeated resistance genes under field conditions in
Syria.
In Yemen, virulence of yellow rust observed in 2001 and 2002 based on
natural infection of the pathogen showed the presence of virulence against
resistance genes Yr7, Yr9, Yr10, YrA, Yr12, Yr17, Yr18, Yr24 and Yr27.
Virulence on Yr3, Yr6, and Yr8 were observed in 1999 but were not recovered
during the 2001 and 2002 survey. This could be due to poor development of
the winter cultivars that carry these genes.
In Egypt, race 242E100 possessed virulence for Clement, Suwon 92×Omar,
Moro, Lee, Spaldings Prolific, Carstens V and Heines Peko. This race,
therefore, has virulence for the resistance conferred by Yr9, Yr SU, Yr10, YrSP,
YrCV, Yr2 and Yr6. Race 0E0 was avirulent to all European and World
differential cultivars, but virulent to Yr2. Race 458E45 reported in Egypt was
virulent on Triticum spelta var. album, Clement, Vilmorin 23, Suwon 92 ×Omar,
Carstens V, Nord Desprez, Heines Peko and Hybrid 46, and therefore has
virulence for Yr9, YrSU, Yr3, YrCV, Yr2, Yr6, Yr5 and Yr4. Virulence
frequencies in the yellow rust population on the differential genotypes tested
in the trap nurseries were above 70% for resistance genes Yr6, Yr7, YrA and
Yr9; however, virulence frequencies for Yr3V and YrSD was less than 5%.
Virulence frequencies on all other lines were between 15 and 70%. These
results reveal a broad virulence spectrum of P. striiformis under natural field
conditions.
At present 30 genes are catalogued for resistance to yellow rust (McIntosh,
Wellings and Park, 1995), and over 38 resistance genes identified against leaf
rust and 48 against stem rust. A majority of these are race specific, and
virulence has been identified for most of them at least somewhere in the
CWANA region. Bread wheat cultivars that carry resistance based on a single
race-specific gene, or combinations of two of them, are currently grown on a
large area in countries where yellow rust has caused major losses or threats in
past years, of which development of yellow rust in Pakistan in 2005 is a good
example.