title: The past, present and future of breeding rust resistant wheat.
abstract: Two classes of genes are used for breeding rust resistant wheat. The first class, called R (for resistance) genes, are pathogen race specific in their action, effective at all plant growth stages and probably mostly encode immune receptors of the nucleotide binding leucine rich repeat (NB-LRR) class. The second class is called adult plant resistance genes (APR) because resistance is usually functional only in adult plants, and, in contrast to most R genes, the levels of resistance conferred by single APR genes are only partial and allow considerable disease development. Some but not all APR genes provide resistance to all isolates of a rust pathogen species and a subclass of these provides resistance to several fungal pathogen species. Initial indications are that APR genes encode a more heterogeneous range of proteins than R proteins. Two APR genes, Lr34 and Yr36, have been cloned from wheat and their products are an ABC transporter and a protein kinase, respectively. Lr34 and Sr2 have provided long lasting and widely used (durable) partial resistance and are mainly used in conjunction with other R and APR genes to obtain adequate rust resistance. We caution that some APR genes indeed include race specific, weak R genes which may be of the NB-LRR class. A research priority to better inform rust resistance breeding is to characterize further APR genes in wheat and to understand how they function and how they interact when multiple APR and R genes are stacked in a single genotype by conventional and GM breeding. An important message is do not be complacent about the general durability of all APR genes.
authors.affiliation: Commonwealth Scientific and Industrial Research Organisation, Agriculture Flagship Canberra, ACT, Australia.
authors.forename: Jeffrey G
authors.initials: JG
authors.lastname: Ellis
authors.affiliation: Commonwealth Scientific and Industrial Research Organisation, Agriculture Flagship Canberra, ACT, Australia.
authors.forename: Evans S
authors.initials: ES
authors.lastname: Lagudah
authors.affiliation: Commonwealth Scientific and Industrial Research Organisation, Agriculture Flagship Canberra, ACT, Australia.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Spielmeyer
authors.affiliation: Commonwealth Scientific and Industrial Research Organisation, Agriculture Flagship Canberra, ACT, Australia.
authors.forename: Peter N
authors.initials: PN
authors.lastname: Dodds
keywords: GM wheat; Puccinia; adult plant resistance (APR); disease resistance gene; wheat biotechnology; wheat rust