Yr26 is a major resistance gene that has been widely deployed in China, especially in the Sichuan Basin since the 1990s, because of its effectiveness against the then predominant races, CYR32 and CYR33. However, new emerging races virulent against Yr26, designated V26/CM42 and V26/Gui22, were detected in the Sichuan Basin since 2008. These virulent strains have not been not reported yet in other wheat growing regions (1). In addition, it has been suggested that Yr26 and Yr24 are the same gene (2).
Although the current value of Yr26 in breeding programs is lower, it can still have a limited application in regions not affected by the new virulent strains if stacked with other genes. Also, the availability of molecular markers is a useful tool to check the presence in other cultivars and decide if other introgressions are required.
Yr26 is located near the centromeric region of chromosome 1B, in the deletion bin C-1BL-6-0.32. Zhang et al. (3) developed a mapping population of 2341 F2 lines derived from a cross between genotype Avocet S (AvS) and the resistant line 92R137 carrying Yr26. Besides, the ESTs mapped to the deletion bin were used to develop polymorphic markers to improve the location of Yr26. The sequences of the wheat ESTs were also used to identify collinear regions in the genome sequences of Brachypodium distachyon and rice, which were found on chromosome 3 for the former, and chromosome 10 for the latter. This information was used to found conserved coding sequences and derive a further set of 358 conserved primers. The resulting map contained several co-segregating and completely linked markers to Yr26. In the next section only two of each class were selected, but Ref. 3 contains complete data for the others.
Markers for Yr26
CON-4 is a marker derived from EST CJ883804 and is located on the proximal side at 0.08 cM of Yr26. CON-6 and CON-10 were completely linked to Yr26 in the mapping population and they were derived from ESTs CD939050 and CJ550732, respectively. STS-BQ74 (derived from BQ169964) maps on the distal side at 0.43 cM.
Primer sequences:
CON-4
CON-4-F 5'- GTG CTG TAC CTG ACG ACG GA -3'
CON-4-R 5'- GTG GAG ATG TTG GGC TTG G -3'
annealing temperature: 58°C
CON-6
CON-6-F 5'- GCC GAT GGG GAA CTG AAT -3'
CON-6-R 5'- GTT GAA CCG CTT GAA CAC C -3'
annealing temperature: 53°C
CON-10
CON-10-F 5'- ATA CTT CAG GAA AAT GTT CGA -3'
CON-10-R 5'- TTT ATT AGG TTG CTT TAG GG -3'
annealing temperature: 53°C
STS-BQ74
STS-BQ74-F 5'- TGG ATG AAC CAA CGA TAG T -3'
STS-BQ74-R 5'- TGG GAA ACA CTT GAC TGC -3'
annealing temperature: 53°C
PCR conditions:
- Denaturing step: 94°C, 4 min
- Amplification step (35 cycles):
- 94°C, 1 min
- 55°C, 1 min (check for specific pairs above)
- 72°C, 1 min
- Extension step: 72°C, 10 min
PCR reaction mix
- 1 U Taq DNA polymerase
- 1.5 µl of 10X buffer (50 mmol KCl, 10 mmol Tris-HCl, pH 8.3)
- 2.0 mmol MgCl2
- 200 µmol each dNTP
- 0.6 µmol of each primer
- 50-100 ng template DNA
Total: 15 µl
PCR products were separated in either 6% or 8% denaturing polyacrylamide gels or 1.5% agarose gels, depending upon the marker. Polyacrylamide gels were stained with silver and agarose gels with ethidium bromide.
References
1: Emerging Yr26-virulent races of Puccinia striiformis f. tritici are threatening wheat production in the Sichuan Basin, China. Han DJ, Wang QL, Chen XM, Zeng QD, Wu JH, Xue WB, Zhan GM, Huang LL, Kang ZS. In: Plant Disease, 2015, 99:754-760. DOI:10.1094/PDIS-08-14-0865-RE.
2: Molecular mapping of stripe rust resistance gene YrCH42 in Chinese wheat cultivar Chuanmai 42 and its allelism with Yr24 and Yr26. Li GQ, Li ZF, Yang WY, Zhang Y, He ZH, Xu SC, Singh RP, Qu YY, Xia XC. In: Theoretical and applied genetics, 2006, 112:1434-1440. DOI: 10.1007/s00122-006-0245-y.
3: Fine mapping of wheat stripe rust resistance gene Yr26 based on collinearity of wheat with Brachypodium distachyonand rice. Zhang X, Han D, Zeng Q, Duan Y, Yuan F, Shi J, Wang Q, Wu J, Huang L, Kang Z. In: PLoS One, 2013, 8(3):e57885. DOI: 10.1371/journal.pone.0057885.