Leaf rust resistance gene Lr21

Contributed by Allan Fritz

Aegilops tauschii, the D-genome progenitor of common wheat (Triticum aestivum), has been a rich source for resistance to Puccinia triticina. To date, six named genes have been described (reviewed in ref. 1, 2). One of the first genes transferred was Lr21 (3). This gene appears to be common in Ae. tauschii, as it has been transferred from several different accessions to T. aestivum (4). The data from Huang and Gill (4) indicate that Lr21 and Lr40 are allelic.

While this gene has been known for some time, it has not been widely used. According to the Cereal Disease Laboratory’s database, the only North American cultivar that carries Lr21 is AC Cora. Lr21 provides resistance to the current spectrum of P. triticina races in the Southern Great Plains. Huang and Gill (4) reported a PCR-based marker that co-segregates with all reported sources of Lr21.

Markers for Lr21

Talbert et al. (5) developed a PCR method based on the sequence of RFLP clone KSUD14. You can find additional information about this marker in Ref. 4.

Primer Sequences:

D14-L       5'- CGC TTT TAC CGA GAT TGG TC -3'

D14-R       5'- CCA AAG AGC ATC CAT GGT GT -3'

Protocol (25 µl reaction):

  • 100-350 ng template DNA
  • 1 pmol each primer
  • 1 unit of Taq DNA polymerase
  • 1.25 µl 50 mM MgCl2
  • 2.5 µl 10X buffer
  • 2 µl 2.5mM dNTPs

PCR Program:

  • Denature for 5 minutes at 94°C.
  • 30 cycles of 94°C for 1 minute, 50° C for 1 minute and 72° C for 2 minutes.
  • The last cycle is 72° C for 5 minutes.

Following amplification, the products are digested with Msp I in a 15-µl reaction containing 1.5 µl of 10X buffer and 10 units of enzyme at 37° C for 3 hours and then separated in 2.2% agarose gels at 35 V constant voltage.

The diagnostic fragment is 885-bp in length.

Lr21
All TA lines except TA1704 carry an Lr21 allele. The 885-bp band (yellow asterisk) is diagnostic for Lr21. TA1704 is susceptible to leaf rust and has a 1.0 kb fragment.

Available germplasm

KS94U215 is the donor used by the backcrossing programs within the IFAFS project. The line has not been formally released, but is available upon request. Requests can be addressed to Allan Fritz or to Gina Brown-Guedira. 

There are other possible sources for transferring Lr21: KS86WGRC02 (HRW), KS89WGRC07 (HRW), KS92WGRC15 (HRW) and AC Cora (HRS).

Conditions presented here should be considered only as a starting point of the PCR optimization for individual laboratories.

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. 

2. Chromosome location of leaf rust resistance gene Lr43 from Aegilops tauschii in common wheat. Hussien, T.; Bowden, R.L.; Gill, B.S.; Cox, T.S. In: Crop Science, 1997, 37(6):1764-1766.

3. Inheritance in hexaploid wheat of leaf rust resistance and other characters derived from Aegilops squarrosa. Kerber, E.R.; Dyck, P.L. In: Canadian Journal of Genetics and Cytology, 1969, 11:639-647.

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. 

5. Evaluation of "sequence-tagged-site" PCR products as molecular markers in wheat. Talbert, L.E.; Blake, N.K.; Chee, P.W.; Blake, T.K.; Magyar, G.M. In: Theoretical and Applied Genetics, 1994, 87(7):789-794. 

Tags

leaf rust resistance