ABSTRACT
Background Rust fungi are a large group of obligately biotrophic basidiomycete fungi that completely depend on their living host tissue for growth and reproduction. Wheat (Triticum aestivum L.) is a host to three dierent rust fungi, causing stripe (yellow), leaf (brown) and stem (black) rust. Wheat stripe rust, caused by Puccinia striiformis Westend. f. sp. tritici Eriks. (Pst), is a serious problem in all major wheat growing countries [1,2]. In the United States, the disease is most destructive in the western United States and has become increasingly important in the south-central and south-eastern states [1,3,4]. Unlike the stem rust (P. graminis f. sp. tritici) and leaf rust (P. triticina) fungi, Pst does not have a known alternate host to complete the sexual cycle. During infection, urediniospores of Pst germinate on wheat leaf surfaces to produce germ tubes. Depending upon the isolate, Pst forms noticeable or unnoticeable appressoria [5,6], from which an infection peg is formed and penetrates a leaf stoma, followed by infection hyphae that form haustorial mother cells, and a specialized infection structure called the haustorium forms and an intimate feeding relationship is established. Haustoria are essential
for rust fungi to take nutrients from their host [7-10] and have also been shown to be involved in vitamin synthesis [11].
