Meeting the Challenge of Yellow Rust in Cereal Crops - ICARDA

The wheat stripe rust pathogen oversummers on volunteer wheat and
possibly certain species of Aegilops, Agropyron, Bromus and Elymus in Europe
(Stubbs, 1985). Stripe rust uredospores can be wind-borne in a viable state for
at least 800 km (Zadoks, 1961). O’Brien et al. (1980) reported the introduction of
wheat stripe rust to Australia, which was probably aided by man. In 1980, the
pathotype first found in Australia appeared in New Zealand, presumably
having been air-borne from Australia, a distance of approximately 2000 km
(Beresford, 1982). In Iran, yellow rust epidemics were recorded during the
1993/94 and 1994/95 seasons (Torabi et al., 1995), with crop losses estimated at
1.5 and 1 million tonne, respectively. In Yemen and Ethiopia, early yellow rust
epidemics have been recorded since 1988 (Mamluk, EL-Naimi and Hakim,
1996). Torabi et al. (2001) noted that the majority of Iranian yellow rust
pathotypes had virulence on plant with genes Yr2, Yr6, Yr7, Yr9, Yr22, Yr23
and YrA. Surveys of Pst pathotypes and the genetic variation within the
pathotypes are important and valuable information for the breeding
programme. This study reports on the prevailing pathotypes of the wheat
yellow rust pathogen in Iran.
53
Materials and methods
For this study, 15 isolates of stripe rust agent were collected from different
parts of Iran, including Gazvein, Mogan, Dezful, Islam Abad, Hamadan, Sari,
Maneh, Mashhad, Borojerd, Darab, Gachsaran and Ahvaz, Yazd, with one
isolate from Kyrgyzstan. Spores of each isolate, after increasing, were
inoculated on an international standard differential set of yellow rust 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 varieties that included
Federation*4/Kavkas (Yr9), Anza (YrA), Avocet R (YrA), Kalyansona (Yr2),
Triticum spelta var. album (Yr5), TP981 (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. Inoculation conditions consisted of a tray with a base tray
containing 2 cm of tap water. After inoculation, the seedlings were placed in
the 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 a
greenhouse. The temperature was maintained at 18 to 19°C for yellow rust.
Infection types were recorded 16–19 days after inoculation, depending upon
the disease and temperature. The objective was to record reactions when the