Why can I see early yellow rust when the variety’s AHDB rating is high?
Wheat yellow rust resistance ratings on the AHDB Recommended List for cereals are based on assessments of the performance of varieties at the adult plant stage. The 1-9 scale, where a high figure shows high resistance, isn’t a guide to likely disease levels on seedlings and juvenile plants in the winter and spring.
So, what’s the difference between adult and juvenile resistance?
Currently, very few varieties have all-stage yellow rust resistance, which is expressed throughout the life-cycle of the wheat plant. The majority are susceptible at the seedling stage and become resistant in later stages, as adult plant resistance (APR) is expressed.
Resistance at any growth stage is dependent on the race of the yellow rust pathogen present. New races regularly appear and certain yellow rust ratings on the AHDB Recommended List may need to be revised downwards.
How are breeders working to improve resistance?
All-stage resistance, sometimes known as seedling resistance, is generally controlled by a single gene which may be effective against all races or just some races. Adult plant resistance (APR) is generally controlled by several resistance genes. The more genes that are stacked together in a variety, the more seasons the resistance is likely to remain effective.
Any take-home messages?
It’s important to monitor all wheat crops in the winter and spring, even if a variety has a high yellow rust resistance rating.