Wheat Leaf Rust Caused by Puccinia triticina

Authors: Bolton, Melvin; Kolmer, James; Garvin, David

Submitted to: Molecular Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/15/2008
Publication Date: 8/1/2008
Citation: Bolton, M.D., Kolmer, J.A., Garvin, D.F. 2008. Wheat Leaf Rust Caused by Puccinia triticina. Molecular Plant Pathology. 9(5):563-575.

Interpretive Summary: Wheat is grown widely around the world, and in most locales this crop faces infection by the fungus Puccinia triticina, which causes the disease leaf rust. Leaf rust has a long recorded history of damaging wheat dating back millenia. Genetically-based resistance has been used by wheat breeders to reduce leaf rust damage; at least 60 individual leaf rust resistance genes have been identified in wheat. The remarkable ease by which P. triticina overcomes most of these resistance genes can be attributed to large populations of the pathogen and strong selection pressure from individual resistance genes leading to proliferation of mutant forms that are able to sidestep detection by individual resistance genes. In a few instances, P. triticina has not been able to overcome genetic resistance, and the wheat genes that confer this resistance have been particularly valuable for improving leaf rust resistance worldwide. Recent research has led to the isolation of leaf rust resistance genes from wheat, and identification of a few genes of P. triticina that play a role in pathogenesis. A more detailed understanding of the biological process by which P. triticina infects wheat, coupled with information on how wheat resists such infection, should reveal new opportunities to develop transgenic methods to control leaf rust. This will result in more secure wheat yields and increased grower profits.

Technical Abstract: Leaf rust, caused by Puccinia triticina, is the most common rust disease of wheat. The fungus is an obligate parasite capable of producing infectious urediniospores as long as the host remains healthy. Urediniospores can be wind-disseminated hundreds of kilometers and may result in wheat leaf rust epidemics on a continental scale. This review summarizes current knowledge of the P. triticina/wheat interaction with emphasis on the infection process, molecular aspects of pathogenicity, rust resistance in wheat, genetics of the host parasite interaction, and the population biology of P. triticina. Puccinia triticina Eriks. belongs to the kingdom Fungi, phylum Basidiomycota, class Urediniomycetes, order Uredinales, family Pucciniaceae, genus Puccinia. Telial (primary) hosts include common wheat (Triticum aestivum L.), durum wheat (T. turgidum L. var. durum), Aegilops speltoides, and goatgrass (Ae. cylindrica). Pycnial-aecial (alternate) hosts are Thalictrum speciosissimum (=T. flavum glaucum) and Isopyrum fumaroides. Leaf rust is characterized by the uredinial stage. Uredinia are up to 1.5 mm in diameter, erumpent, round to ovoid, with orange to brown colored pustules that are scattered on both the upper and lower leaf surfaces of the primary host. Uredinial infections produce urediniospores that average 20 m in diameter, are sub-globoid and orange-brown, with up to eight germ pores scattered in thick, echinulate walls. Telia develop beneath the leaf epidermis and are the size of uredia, are erumpent and glossy black. Teliospores are two-celled and are round or flattened at the apex. Pycnia and aecia develop on the alternate hosts. Wheat varieties that are fully susceptible have large uredinia lacking chlorosis or necrosis. Resistant wheat varieties are characterized by various responses from small hypersensitive flecks to small to moderately-sized uredinia that may be surrounded by chlorotic and/or necrotic zones.