Meeting the Challenge of Yellow Rust in Cereal Crops - ICARDA

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Materials and methods
This study was carried out on Karaj station with 53 isolates of stripe rust
collected from different parts of Iran. Spores of each isolate, after
multiplication, were inoculated on an international standard yellow rust
differential set of wheat lines in the greenhouse. A set of the World (8
genotypes) and European (8 genotypes) wheat yellow rust differentials, as
proposed by Johnson et al. (1972), was used in the study, in addition to 10
supplementary genotypes, namely Federation*4/Kavkas (Yr9), Anza (YrA),
Avocet R (YrA), Kalyansona (Yr2), Triticum spelta var. album (Yr5), TP 981
(Yr25), Meering 24 (Yr24), Bolani (susceptible check), Avocet S and TP 1295.
For inoculation, uredospores were mixed with talcum powder (1:4). After
each inoculation, spray equipment was thoroughly washed in water and dried
in an oven at 60°C to avoid contamination when successively inoculating with
different pathotypes. After inoculation the seedlings were placed in trays and
covered with plastic hoods. Trays were placed in an incubation room at 10°C,
where the differential temperatures between the water and room temperature
resulted in dew formation. Seedlings were held for 24 h at 10°C and 100% RH
in the dark. Following incubation, plants were moved to the greenhouse and
maintained at 18–19°C. Infection types were recorded 16–19 days after
inoculation, depending upon the disease and temperature. The objective was
to record reactions when the difference between the controls and the test lines
were at their maximum. Infection types were recorded using the scale (0–9)
described by McNeal et al. (1971).
Results and Discussion
Stripe rust is the most serious disease of wheat in CWANA, including Iran.
The development of resistant cultivars is the most effective, safe and
economical method of control. However, stripe rust pathogenic variation
remains the underlying reason for elusive rust resistance. Genetic variation in
the stripe rust pathogen is continuously evolving in CWANA.
In greenhouse tests, among 53 Iranian collections, 28 pathotypes were
determined (Table 1). The stripe rust population in the region consists of a
number of pathotypes that differ in their pathogenicity on the host plant.
According to the results, virulence on plants with gene(s) Yr2, Yr6, Yr7, Yr8,
Yr9, Yr24, Yr25, Yr27, YrSD, YrSP, Yr3N, Yr2+, Yr6+, Yr9+, Yr7+, Yr32+ and
YrA was detected. The majority of isolates showed virulence on plant with Yr2,
Yr6, Yr7, Yr9, YrA and Yr24 genes. No virulence was detected on plants with
Yr1, Yr3V, Yr4, Yr5, Yr10 or YrSU. Torabi et al. (2002) noted that virulence was
not detected for plant with genes Yr1, Yr4, Yr5 and Yr10, and virulence on
plant with genes Yr2, Yr6, Yr7, Yr9, Yr22, Yr23 and YrA was common in Iran.
Of these virulences, pathotypes possessing the combination of virulence