Because new differentials were developed, the nomenclature of P. striiformis f. sp. tritici races was modified. First, the number system, similar to the previous PST series (3,12), was used with a “PSTv” prefix which designates a specific race of virulence or avirulence response on the differential set. For example, PSTv-1 is given to a race which is virulent to Yr1 and avirulent to the remaining 17 Yr gene lines in the new differential set. The prefix “PSTv” stands for P striiformis f. sp. tritici virulence. The “v” is included in the prefix is to distinguish the new race names from the previous “PST” races.
Second, an octal system, which is similar to the letter-coding systems for naming races of P. graminis f. sp. tritici (15) and P. triticina (18), was used for coding P. striiformis f. sp. tritici races. The 18 Yr single-gene differentials were grouped into six sets, each with 3 differentials (Table 2). Numbers 0 to 7 were used to code all eight possible virulence or avirulence patterns for each set of three differentials. For each race (virulence patterns on the 18 differential lines), a code of six digits can be obtained.1
This octal system was later revised in 2016 to follow the normal octal notation proposed by others. (Table 2). The normal octal notation corresponds nicely to a binary notation which will allows for easier use in computerized programs. Due to this modification, the octal codes for the races PSTv-1 to PSTv-41 have been revised and will follow the normal octal notation from 2016-present.2
For example, PSTv-41 has an octal code of 3757441 which indicates that PSTv-41 has an octal number of 3 when tested with the first differential set (AAV to Yr1, Yr5, and Yr6 respectively), an octal number of 7 when tested with the second differential set (VVV to Yr7, Yr8, and Yr9 respectively), and so on.
| Yr Gene Set | Yr Gene | ||
|---|---|---|---|
| 1 | Yr1 | Yr5 | Yr6 |
| 2 | Yr7 | Yr8 | Yr9 |
| 3 | Yr10 | Yr15 | Yr17 |
| 4 | Yr24 | Yr27 | Yr32 |
| 5 | Yr43 | Yr44 | YrSP |
| 6 | YrTr1 | YrExp2 | YrTye |
| Code | Previous OC | Reaction | ||
|---|---|---|---|---|
| 0 | 0 | A | A | A |
| 1 | 3 | A | A | V |
| 2 | 2 | A | V | A |
| 3 | 6 | A | V | V |
| 4 | 1 | V | A | A |
| 5 | 5 | V | A | V |
| 6 | 4 | V | V | A |
| 7 | 7 | V | V | V |
Races of Puccinia striiformis f. sp. tritici are identified using the virulence (V)/ avirulence (A) reactions of an isolate across the Yr single-gene line set of wheat differentials.
References
- Wan, A. M., and Chen, X. M. 2014. Virulence characterization of Puccinia striiformis sp. tritici using a new set of Yr single-gene line differentials in the United States in 2010. Plant Disease 98:1534-1542. doi:10.1094/PDIS-01-14-0071-RE.
- Wan, A. M., Chen, X. M., and Yuen, J. 2016. Races of Puccinia striiformis f. sp. tritici in the United States in 2011 and 2012 and comparison with races in 2010. Plant Dis. 100:966-975.