ABSTRACT
Two distinct categories of rust resistance genes have been identified: all-stage resistance (ASR) genes (previously referred to as seedling resistance genes) and adult plant resistance (APR) genes. These designations reflect the developmental stage of the host plant when
Table 2 Cloned rust resistance genes in wheat
Species Genea Product Rust pathogen Reference
Triticum aestivum
Lr1 NBS-LRR protein Pt Cloutier et al. (2007)
T. aestivum Lr10 NBS-LRR protein Pt Feuillet et al. (2003)
Aegilops tauschii
Lr21 NBS-LRR protein Pt Huang et al. (2003)
T. aestivum Lr34/Yr18/Sr57/ Pm38
ABC transporter Multiple pathogens
Krattinger et al. (2009)
T. aestivum Lr67/Yr46/Sr55/ Pm49
Hexose transporter
Multiple pathogens
Moore et al. (2015)
T. monococcum/ T. boeoticum
Sr22 NBS-LRR protein Pgt Steuernagel et al. (2016)
Ae. tauschii Sr33 NBS-LRR protein Pgt Periyannan et al. (2013)
T. monococcum Sr35 NBS-LRR protein Pgt Saintenac et al. (2013)
Ae. tauschii Sr45 NBS-LRR protein Pgt Steuernagel et al. (2016)
Secale cereale Sr50 NBS-LRR protein Pgt Mago et al. (2015)
T. spelta Yr10 NBS-LRR protein Pst Liu et al. (2014)
T. dicoccoides Yr36 START domain kinase
Pst Fu et al. (2009)
the resistance phenotype is expressed, with ASR genes providing resistance throughout plant growth and APR genes protecting plants only in the latter stages of development. Over 90% of catalogued rust resistance genes provide ASR; however, these genes generally do not provide resistance to all isolates or races of a rust pathogen species, that is, they are race-specific resistance genes. ASR genes tend to provide higher levels of disease resistance but have limited efficacy in the field as they can be rapidly overcome by pathogen mutation to virulence, the underlying molecular basis of which is described below. In contrast, APR genes generally provide partial resistance only and can be either race-specific or race-non-specific. There is increasing evidence for race-specific APR genes of major effect, particularly for stripe rust resistance (Johnson 1988; Hao et al. 2011; Staphit et al. 2012; Sørensen et al. 2014). One possibility is that structurally and mechanistically race-specific APRs are really ASRs that have poor seedling expression.
