Disease resistance. Stripe rust.

Yr5

Background information

Stripe rust is one of the most aggressive diseases on common wheat (Triticum aestivum L. ) and durum wheat (T. turgidum L. var. durum) worldwide. In the United States, the western states are the most affected, although is becoming more important in the central US. Stripe rust is caused by the fungus Puccinia striiformis Westend. f. sp. tritici Eriks. (P. s. tritici).

The preferred way of controlling the disease is through the use of resistant varieties. There are several genes that can express resistance to this disease. However, changes in pathogen virulence can render them useless for breeding after some time.

Yr5 was described first in 1966 by Macer in Triticum spelta album (1). This gene confers resistance to all of the races known in the US (X. M. Chen, personal communication). Yr5 is located on chromosome arm 2BL, 21 cM away from the centromere (2). Kema transferred this gene into some commercial cultivars (3).

Methods

Yan et al. found some RGAP (resistance gene analog polymorphism) markers completely linked to Yr5 (4). This type of markers are obtained by PCR amplification of sequences known to be homologous to conserved domains of genes coding for disease resistance (5). Usually, many products are obtained, and those that co-segregate with the trait in a mapping population can be used as markers. However, this type of markers are difficult to use and score, specially in a breeding environment, besides in some cases they are not polymorphic for the recurrent parent.

Later, Chen et al (In press) converted two of the RGAP markers into more user friendly PCR markers. They developed two STS (sequence tagged site) and one CAPS (cleaved amplified polymorphic sequence) markers. These markers are polymorphic for a wider range of recurrent parents. The STS markers are analyzed in polyacrylamide gels, but they are easier to score than the original RGAPs, and the CAPS marker can be resolved in agarose gels. For experimental details see the methods section.

Available germplasm

The breeding programs from this project use the line Avocet/Yr5 (Yr5/6*AVS) as the donor of Yr5. This donor line was developed at the Plant Breeding Institute, Sydney, Australia by backcrossing the Yr5 gene donor, Triticum spelta album, with the recurrent susceptible spring wheat genotype Avocet.

Current backcrossing programs for Yr5 resistance gene within the project

Laboratory codes: CA, University of California, Davis; WA, Washington State University.

Additional information.

Reaction to PST races of P. striiformis f. sp. tritici

References

1. The formal and monosomic genetic analysis of stripe rust (Puccinia striiformis) resistance in wheat. Macer, RCF. In: IJ. Mackey (ed.) Proc. of 2nd Int. Wheat Genet. Symp. Lund, Sweden 1963. Hereditas Suppl., 1966, 2:127-142.

2. Genetic control of yellow rust resistance in T. spelta album. Law CN. In: Plant Breeding Institute, Cambridge, Annual Report 1975, 1976, 108-109.

3. Resistance in spelt wheat to yellow rust I. Formal analysis and variation for gliadin patterns. Kema GHJ. In: Euphytica, 1992, 63:207-217.

4. Resistance gene analog polymorphism markers co-segregating with the Yr5 gene for resistance to wheat stripe rust have homology with plant disease resistance genes. Yan GP, Chen XM, Line RF, Wellings CR. In: Theoretical and Applied Genetics, 2003, 106:636-643. [abstract]

5. Isolation of a superfamily of candidate disease resistance genes in soybean based on a conserved nucleotide-binding site. Yu YG, Buss GR, Maroof MA. In: Proc Natl Acad Sci USA, 1996, 93:11751-11756. [abstract]

6. Development of Sequence Tagged Site and Cleaved Amplified Polymorphic Sequence Markers for Wheat Stripe Rust Resistance Gene Yr5. Chen XM, Soria MA, Yan GP, Sun J, Dubcovsky J. In: Crop Science, 2003, In press. [abstract]