Meeting the Challenge of Yellow Rust in Cereal Crops - ICARDA

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Pathotyping of wheat stripe
[yellow] rust over the last three
years in Iran
F. Afshari
Seed and Plant Improvement Institute, P.O. Box 4119, Karaj, Islamic Republic of Iran
Introduction
The occurrence of pathogenic variability in rust fungi led to considerable
confusion and disagreement among early researchers of rust diseases. For
example, Rudorf (1929; cited in Wellings, 1986) noted that some cultivars
resistant in the USA were susceptible in Germany. This was due presumably to
variation in pathogenic attributes between geographical regions. Wheat is a
host for many groups of parasitic fungi, bacteria, viruses and insects. Major
threats to wheat production on a worldwide basis come from one or more of
the three rust diseases. Yellow rust caused by Puccinia striiformis West. f.sp.
tritici (Pst) is the most important rust disease in Iran. The annual cost due to
stripe [yellow] rust in Australia in terms of yield lost and control costs was
estimated to be $AUS 139 million (Brennan and Murray, 1988). In 1994, an
estimated 15% (1.5 million tonne) of the national wheat yield was lost in Iran
due to yellow rust (Torabi et al., 1995).
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
more than 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 in
1993 and 1995 (Torabi et al., 1995), and crop losses were 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. (2002) 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 Pst pathotypes in Iran.