Analysis of the Lr34/Yr18 Rust Resistance Region in Wheat Germplasm

Abstract

The Lr34/Yr18 adult plant resistance gene contributes significantly to durable leaf rust (caused by Puccinia triticina Eriks.) resistance. Simple and robust molecular markers that enable early detection of Lr34/Yr18 are a major advancement in wheat (Triticum aestivum L.) breeding. An insertion/deletion size variant located at the csLV34 locus on chromosome 7D within an intron sequence of a sulfate transporter‐like gene tightly linked to the Lr34/Yr18 dual rust resistance gene was used to examine a global collection of wheat cultivars, landraces, and D genome–containing diploid and polyploid species of wheat relatives. Two predominant allelic size variants, csLV34a and b, found among the wheat cultivars showed disparate variation in different wheat growing zones. A strong association was observed between the presence of Lr34/Yr18 and the csLV34b allele and wheat lines known to have Lr34/Yr18 that had the csLV34a allele were rare. All landraces with the exception of those from China were predominantly of the csLV34a type. Only one size variant, csLV34a, was detected among the diploid and polyploid D genome–containing species, indicating that csLV34b arose subsequent to hexaploid bread wheat synthesis. The lineage of the csLV34b allele associated with Lr34/Yr18 in modern wheat cultivars from North and South America, CIMMYT, Australia, and Russia was tracked back to the cultivars Mentana and Ardito developed in Italy by Nazareno Strampelli in the early 1900s. The robustness of the csLV34 marker in postulating the likely occurrence of Lr34/Yr18 across a wide range of wheat germplasm and its utility in wheat breeding was confirmed.

Gene-specific markers for the wheat gene Lr34/Yr18/Pm38 which confers resistance to multiple fungal pathogens

“…Two wheat cultivars, Jagger and H45, classified as susceptible to leaf rust and stripe rust respectively on adult plants were shown to have Lr34-associated alleles of the csLV34 marker (Kolmer et al 2008). Additional tests with the gene-specific markers confirmed that both cultivars indeed carry the Lr34 gene (Table 3).…”

“…Another cultivar, Cappelle Desprez, was postulated to have Lr34 based on the observed genetic association of leaf and stripe rust resistance (McIntosh 1992 The Canadian cultivar, AC Domain was postulated to contain Lr34 (Kolmer 1996) and also carries the Lr34-linked allele at the csLV34 locus (Kolmer et al 2008). Two wheat cultivars, Jagger and H45, classified as susceptible to leaf rust and stripe rust respectively on adult plants were shown to have Lr34-associated alleles of the csLV34 marker (Kolmer et al 2008).…”

“…Leaf tip necrosis (Ltn), a morphological marker which under certain environmental conditions can be used to predict the presence of Lr34 was previously assessed in 127 wheat genotypes at CIMMYT, Mexico (Kolmer et al 2008). Furthermore, additional adult plant rust resistance genes other than Lr34 or Lr46/Yr29 must be present in the 13 genotypes, as only a subset of them have been predicted to carry Lr46/Yr29 (Kolmer et al 2008).…”

“…The gene was first characterized in Canada by Dyck (1977;1987), but Lr34-containing germplasm has been used in cross-bred cultivars since the early part of the 20 th century. Three breeding lineages of Lr34 in wheat germplasm have been identified: They consist of (i) Far-East germplasm, (ii) spring wheat lines from North and South America that were traced back to Lr34 cultivar sources developed in Italy and (iii) some winter wheat material in Europe (Kolmer et al 2008). …”

“…After considerable effort, two markers SWM10 (Bossolini et al 2006) and csLV34 ) closely linked to the Lr34/Yr18/Pm38/Ltn1 locus have been shown to be specific diagnostic tools for this multi-pathogen resistance trait. However, rare recombination events between these markers and Lr34 in certain wheat lineages as well as equivocal gene postulations revealed limitations in the diagnostic specificity of these markers (Kolmer et al 2008;McCallum et al 2008). …”