The Rust Fungi

The rust fungi are a monophyletic group of approximately 7000 species in the basidiomycota and are highly specialized obligate parasites of plants. The life cycle of rusts can be complex. Some rusts have up to five spore stages that alternate between haploid and dikaryotic nuclear conditions and that can occur on two taxonomically unrelated host plants. The rusts have evolved specialized structures that allow them to penetrate and obtain nutrients from living host cells. Biologic forms of a single rust speciesmaydiffer in ability to attackdifferent genera of host plants. Furthermore,within a single rust species they can be highly variable in ability to attack different genotypes of one host species. At the species level, genes that condition avirulence/virulence in rusts interact in a specific relationship with rust-resistance genes in plants. Many of the most important plant diseases in the world are caused by rust fungi.