Disease resistance. Leaf Rust Resistance

Lr29 - Lr25

Contributed by J. Douglas Procunier

Agriculture & AgriFood Canada

Background information

The leaf rust resistance gene Lr29 was transferred from Agropyron elongatum to chromosome 7DS of common wheat. Subsequently, Lr29 was introgressed into Thatcher (Tc) by backcrossing (Tc*6/Lr29) and a line RL6080, near isogenic for the introgressed segment (NIL), was used in this study. Only two isolates from Turkey and one from Pakistan were virulent on seedlings with Lr29 resistance gene in a global survey (7).

The leaf rust resistance gene Lr25 is present in a segment of the rye 2R chromosome transferred to chromosome 4A of wheat by a 4A/2R translocation. The line RL6084, near isogenic for the introgressed segment (NIL) was constructed by repeated backcrossing to Tc (Tc*6/Lr25). Virulence on seedlings with the Lr25 resistance gene has been detected in Algeria, Bulgaria, Canada, China, Egypt, Ethiopia, Hungary, Israel and Pakistan (7).

Methods

Tightly linked RAPD markers for leaf rust resistance genes Lr29 and Lr25 were converted to SCAR markers. The simultaneous identification of both SCAR markers was accomplished by touchdown multiplex PCR. A single, easily resolved band for each marker was visualized on ethidium bromide stained agarose gels. Experimental details are described in the PCR methods section.

Available germplasm

RL6080 (Lr29/Tc) and RL6084 (Lr25/Tc) NIL lines are available from CRC-AAFC. Significantly higher seed protein content was found for cultivars containing the seedling rust resistance gene Lr29. No deleterious effects as flour quality or grain yield are associated with Lr29. However, lines with Lr25 are agronomically inferior to comparable near-isogenic lines lacking the gene, limiting the use of this gene in wheat breeding (6).

References

1. PCR-based RAPD/DGGE markers linked to leaf rust resistance genes Lr29 and Lr25 in wheat (Triticum aestivum L.). Procunier JD, Townley-Smith TF, Fox S, Prashar S, Gray M, Kim WK, Czarnecki E, Dyck PL In: Journal of Genetics and Breeding, 1995, 49: 87-92.

2. The genetic analysis of two interspecific sources of leaf rust resistance and their effect on the quality of common wheat. . Dyck PL, Lukow OM. In: Canadian Journal of Plant Science, 1988, 68:633-639.

3. An appraisal of stem and leaf rust resistance in North American hard red spring wheats and the probability of multiple mutations to virulence in populations of cereal rust fungi. Kolmer JA, Dyck PL, Roelfs AP. In: Phytopathology, 1991, 81:237-239.

4.Agropyron-wheat transfers induced by homoeologous pairing. . Sears ER. In: E.R. Sears and M.L. Sears eds. Proc. 4th Int. Wheat Genet. Symp., 1973, Univ. of Missouri, Colombia, MO, pp 191-199

5. Characteristics of leaf rust transferred from rye to wheat. . Driscoll CJ, Jensen NF. In: Crop Science, 1964, 4: 372-374

6. Wheat Rusts, an Atlas of Resistance Genes. McIntosh RA, Wellings CR, Park RF. Editor: Jean K. (CSIRO, Melbourne, Australia, 1995).

7. Analysis of wheat leaf rust and stem rust virulence on a worldwide basis. Huerta-Espino J., 1992, PhD Thesis, University of Minnesota, USA