Young plant resistance to wheat yellow rust

The pathogen that causes yellow rust – Puccinia striiformis f. sp. tritici – comes in different forms. There are races that only infect particular varieties. To add further complexity, some varieties are susceptible to yellow rust when plants are young, but go on to develop some level of resistance after early stem extension (the ‘adult-plant’ stage).

Unlike adult plant resistance, young plant resistance to yellow rust is effective at all growth stages.

Some varieties are susceptible at the young plant stage but develop some level of adult plant resistance.

Varieties susceptible at the young plant stage may need yellow rust treatment during the T0–T2 fungicide period, even if they have a high level of adult plant resistance (ratings 8 or 9).

• Resistance is categorised using yellow rust isolates, selected by UKCPVS, to best represent the diversity in the pathogen population at the time of testing
• A variety is classified as susceptible at the young-plant stage, if it is susceptible* to any one of the isolates
• Status is presented for recommended and candidate varieties in trial (data is not available for varieties no longer under test in RL trials) 
• As pathogen populations are diverse and can change rapidly, so can resistance status
• As isolates chosen for testing are a subset of the population, actual field performance may vary**

*How susceptibility is assessed

Young plants are scored c. 14 days after inoculation, with average infection type scores calculated. Scores of 2.7 and above indicate a compatible reaction and the isolate is recorded as able to cause disease (virulent) – meaning the variety is susceptible (S) to it. The raw data is published in the corresponding UKCPVS annual report.

**The AHDB Recommended Lists for cereals and oilseeds 2023/24 (December 2022) onwards includes final information on young-plant resistance. RL field trial data (before ear emergence) is used to validate UKCPVS results. This may, for example, result in additional varieties being marked as susceptible in the RL that were marked as resistant in the UKCPVS data set.

The yellow rust population is highly diverse and changeable. It is important that crops are monitored regularly and unexpected disease observations reported to the UK Cereal Pathogen Virulence Survey (UKCPVS).