Meeting the Challenge of Yellow Rust in Cereal Crops - ICARDA

Defence mechanisms against
rust, and genetic engineering
79
R. Haghparast, M. Aghaee, A. Dariaee and R. Mohammadi
Dryland Agricultural Research Institute, Kermanshah, Islamic Republic of Iran
Introduction
Among the diseases that attack wheat, the rusts, namely leaf or brown rust
(Puccinia recondita Rob. ex Desm. f.sp. tritici), stripe or yellow rust (P. striiformis
West. f.sp. tritici) and stem or black rust (P. graminis Pers. f.sp. tritici Eriks &
Henn.) are the most damaging diseases. They inflict heavy losses on three
cultivated species of wheat, namely bread wheat (Triticum aestivum), durum
wheat (T. durum) and emmer or khapli wheat (T. dicoccum). It is estimated that
rust diseases reduce wheat yield worldwide by 15–20%, which suggest a loss
of 20–30 million tonne annually in developing countries (Hanson, Borlaug and
Anderson, 1982). These pathogens are found wherever wheat is grown, but
their importance from area to area depends on the climate and also on the
degree of resistance of predominant cultivars (Knott, 1989). Rust pathogens of
wheat are important as they have caused a number of epidemics in the past in
various major environments of the world (McIntosh, Wellings and Park, 1995;
Nayar and Bhardwaj, 1998). For instance, losses in grain production in severe
epidemics of stripe rust in cool and humid wheat-growing regions has been
recorded up to 70% (Roelfs, 1978). Although chemicals can be used to control
leaf rust, genetic manipulation of host resistance represents the most cost
effective and environmentally safe control measure. However, the existing
disease resistance sources, even those claimed to be durable, provide no
guarantee of remaining effective in the future (Assefa and Fehrmann, 2000).
Due to neutralization of resistance with the evolution of new pathogenic
pathotype(s), breeding for resistance using diverse resistance sources is the
most effective strategy to prolong the life of new cultivars (Sharma and Singh,
2000). Recent evidence is available indicating the possibility of producing
durable resistant against rusts in transgenic wheat. Production of rust resistant
transgenic wheat is possible through better understanding of the molecular
and biochemical mechanisms involved in defence against rust pathogens. In
this review, some of these mechanisms potentially leading to progress in rust
resistance in transgenic wheats are discussed.