A wheat landrace collected in Pakistan, AUS27858, from the Watkins collection showed high levels of resistance against Australian pathotypes of Puccinia striiformis f. sp. tritici (1). The Watkins wheat collection is a set of landraces collected by A. Watkins in the 1920s (2). The current collection has around 1200 accessions, and it is housed at the John Innes Centre Germplasm Resource Unit, in the UK, and at the Australian Winter Cereal Collection, in Tamworth, Australia.
A previous unpublished analysis of an F3 population derived from the cross of AUS27858 with the susceptible parent Westonia indicated that AUS27858 had two stripe rust resistance genes that received the temporary designations YrAW1 and YrAW2. To further characterize YrAW1, Randhawa et al. (1) developed an F6 recombinant inbred line population derived from one of the F3 families.
The multi-pathotype tests showed that YrAW1 is effective against a range of Australian pathotypes of P. striiformis f. sp. tritici that are virulent for stripe rust resistance genes present in the global wheat germplasm.
Using DArT markers YrAW1 was mapped on the long arm of chromosome 4A and was formally designated Yr51. In addition it was confirmed that it is a recessive gene. A series of DArT loci located on 4AL were converted to STS markers and together with SSR, EST-based STS and gene-based markers a more saturated map generated. Yr51 was delimited by 3.7 cM interval between markers owm45F3R3 and sun104. Gene-based marker owm45F3R3 mapped 1.2 cM proximal to Yr51; and STS marker sun104, 2.5 cM distal. Marker sun104 is a dominant marker that yields a PCR product of 225-bp on AUS27858, and does not amplify on Westonia. In a validation panel that included 27 Australian and 13 Indian cultivars that lacked Yr51, none of them amplified sun104. On the other hand, the results with owm45F3R3 were variable and in consequence it is not recommended for MAS programs.
Markers for Yr51
sun104-F 5'- TGC TAT GTG CGT GAT GAT GA -3'
sun104-R 5'- TTA CAT GCT CCA GCG ACT TG -3'
Final concentrations of the PCR mix
- 50 ng genomic DNA
- 1x Immolase PCR buffer (Bioline)
- 0.2 U of Immolase DNA polymerase (Bioline)
- 0.2 mM dNTPs
- 0.2 mM each of forward and reverse primer
Reaction volume: 10µl
- Denaturing step: 95°C, 10 min
- Touchdown step (decrease 1°C/cycle for 6 cycles):
- 92°C, 30 sec
- 65-60°C, 30 sec
- 72°C, 30 sec
- Amplification step (34 cycles):
- 92°C, 30 sec
- 60°C, 30 sec
- 72°C, 30 sec
- Extension step: 72°C, 7 min
sun104 is a dominant marker that only amplifies on lines carrying Yr51 derived from AUS27858, producing a PCR product of 225-bp. No amplification was observed in the cultivars lacking Yr51 tested so far.
1. Molecular mapping of stripe rust resistance gene Yr51 in chromosome 4AL of wheat. Randhawa M,Bansal U, Valárik M, Klocová B, Dolezel J, Bariana H. In: Theoretical and Applied Genetics, 2014, 127:317-324. DOI: 10.1007/s00122-013-2220-8.
2. Exploring wheat landraces for rust resistance using a single marker scan. Bansal UK, Arief V, Delacy IH, Bariana HS. In:Euphytica, 2013, 194:219–233. DOI:10.1007/s10681-013-0940-0.