Disease resistance. Leaf rust.

Lr39

Contributed by Gina Brown-Guedira and Suhkwinder Singh

References

1. Leaf rust-resistance genes Lr41, Lr42 and Lr43 transferred from Triticum tauschii to common wheat. Cox, T.S.; Raupp W.J.; Gill, B.S. In: Crop Science, 1994, 34(2):339-343.

In order to diversify the genetic base of resistance in hard red winter wheat (Triticum aestivum L.) to leaf rust (caused by Puccinia recondita Rob. ex Desm.), five genes for resistance were transferred from the diploid goatgrass T. tauschii (Coss.) Schmal. to hexaploid wheat lines. One of the derived lines, KS90WGRC10, had a very low infection type when inoculated with 23 cultures of P. recondita. The others, KS91WGRC11, KS92WGRC16, U1865, and U1866, had low to intermediate infection types with three cultures. Their infection types varied similarly to those of lines carrying previously transferred alleles of Lr21. WGRC10 carries a completely dominant gene, Lr41, on chromosome ID that segregates independently of any other T. tauschii-derived leaf rust-resistance genes. WGRC11 carries the partially dominant gene, Lr42, also on ID, that is linked to Lr21 with a recombination value of 0.286 +/- 0.023. WGRC16 carries a partially dominant gene, Lr43, that segregates independently of all known genes for seedling resistance from T. tauschii; its chromosome location is not known. The genes carried by U1865 and U1866 are allelic to Lr21. WGRC10, WGRC11, and WGRC16 have been released as germplasms by the Wheat Genetics Resource Center.

2. Registration of KS86WGRC02 Leaf Rust Resistant Hard Red Winter Wheat Germplasm. Gill, B.S.; Raupp, W.J.; Browder, L.E.; Cox, T.S. In: Crop Science, 1988, 28(1):207.

3. Cytogenetic and molecular mapping of the leaf rust resistance gene Lr39 in wheat. Raupp, W.J.; Sukhwinder-Singh; Brown-Guedira, G.L.; Gill, B.S. In: Theoretical and Applied Genetics, 2001, 102(2-3):347-352.

Leaf rust, caused by the fungus Puccinia triticina Eriks, is one of the most serious diseases of wheat (Triticum aestivum AABBDD, 2n=6x=42) worldwide. Growing resistant cultivars is an efficient and economical method of reducing losses to leaf rust. Here we report a new leaf rust resistance gene, Lr39, transferred from Aegilops tauschii into common wheat. Lr39 conditions both seedling and adult plant resistance to the leaf rust pathogen. The inter- and intra-chromosomal mapping of the Lr39 gene showed that it is different from all previously described Lr genes. We used monosomic analysis for the inter-chromosomal mapping and wheat microsatellite markers for the intra-chromosomal mapping. The monosomic and ditelosomic analysis indicated that Lr39 is independent of the centromere on the short arm of chromosome 2D. Eight microsatellite markers for 2DS were used for linkage analysis on a population of 57 F₂ plants derived from a cross of an Ae. tauschii-derived wheat, cv. Wichita line TA4186 (possessing Lr39), with Wichita monosomics for the D-genome chromosomes. The microsatellite marker analysis confirmed the location of the gene on 2DS. Three markers were polymorphic and linked to the gene. The closest marker Xgwm210 mapped 10.7 cM from Lr39. The location of Lr39 near the telomere of 2DS distinguishes it from the Lr2 and Lr22 loci, which are located on 2DS proximal to Xgwm210.

4. An RGA-like marker detects all known Lr21 leaf rust resistance gene family members in Aegilops tauschii and wheat. Huang, L; Gill, B.S. In: Theoretical and Applied Genetics, 2001, 103(6-7):1007-1013.

Leaf rust is one of the most important diseases of wheat worldwide, particularly in the Great Plains region of the USA. One long-term strategy for the control of this disease may be through durable genetic resistance by gene pyramiding. An important step in this strategy is identifying molecular markers linked to different leaf rust-resistance genes. Here we report the molecular tagging of a leaf rust-resistance gene that may have the potential for durable resistance through further genetic manipulation and gene pyramiding. Lr39 was previously designated for a leaf rust-resistance gene introgressed from Aegilops tauschii accession TA1675 into the common wheat germplasm WGRC2. Lr40 was designated for a gene derived from Ae. tauschii accession TA1649 and is present in germplasm WGRC7. These genes are now believed to be allelic to Lr21, which was transferred to wheat from a different accession of Ae. tauschii. Molecular mapping of Lr39 and Lr40 indicates that both genes come from TA1649. WGRC2 and WRGC7 also have a similar infection type against rust culture PRTUS6. We suggest the designation of the gene in WGRC2 should be changed to Lr40. RFLP marker KSUD14 (locus Xksud14) was found 0.2-cM proximal to Lr40 in a WGRC2/Wichita F₂ population (218 individuals), and co-segregated with the gene in a WGRC7/Wichita F₂ population (165 individuals). A PCR-based molecular marker developed from the sequence-tagged-site (STS) of Xksud14 was mapped to the same locus as the RFLP marker KSUD14 in both populations. KSUD14 has the structure of a resistance gene analog (RGA) including kinase2a and kinase3 domains similar to the Cre3 gene of wheat and the rust resistance gene Rp1-D of maize. When the PCR products amplified from KSU14 STS were cleaved with restriction enzyme MspI, an 885-bp fragment was found in WGRC2, WGRC7, the Lr21 near-isogenic line, and eight accessions of Ae. tauschii shown to have resistance gene alleles at the Lr21 locus. The KSUD14 PCR-based assay provides an excellent marker for Lr40 and Lr21 in diverse wheat breeding and wild Ae. tauschii populations.

5. Isolation and mapping of microsatellite markers specific for the D genome of bread wheat. Pestsova, E.; Ganal, M.W.; Röder, M.S. In: Genome, 2000, 43(4)689-697.

The potential of Aegilops tauschii, the diploid progenitor of the D genome of wheat, as a source of microsatellite markers for hexaploid bread wheat was investigated. By screening lambda phage and plasmid libraries of Ae. tauschii genomic DNA, dinucleotide microsatellites containing GA and GT motifs were isolated and a total of 65 functional microsatellite markers were developed. All primer pairs that were functional in Ae. tauschii amplified well in hexaploid wheat. Fifty-five loci amplified by 48 primer sets were placed onto a genetic framework map of the reference population of the International Triticeae Mapping Initiative (ITMI) 'Opata 85' × 'W7984'. The majority of microsatellite markers could be assigned to the chromosomes of the D genome of wheat. The distribution of the markers along the chromosomes is random. Chromosomal location of 22 loci nonpolymorphic in the reference population was determined using nullitetrasomic lines of Triticum aestivum 'Chinese Spring'. The results of this study demonstrate the value of microsatellite markers isolated from Ae. tauschii for the study of bread wheat. The microsatellite markers developed improve the existing wheat microsatellite map and can be used in a wide range of genetic studies and breeding programs.