Niab’s Head of Pathology, Kostya Kanyuka, explains more about what we are seeing so far this year, with samples coming into the UKCPVS and what it might mean:
This spring is turning out to be anything but typical. At several UK trial sites in the North-East of England, the Niab Northern trials team spotted unusually high levels of yellow rust on wheat varieties that are officially rated 8 or 9 for adult plant resistance.
Alarmingly, this includes varieties like KWS Dawsum, Typhoon, and Champion, which also showed strong resistance at the seedling stage in previous seasons.
The UK Cereal Pathogen Virulence Survey (UKCPVS) has also already received a surge of yellow rust samples from these affected varieties from others. We’re now working to determine whether this is the result of a new incursion of yellow rust from outside the UK, or whether we’re looking at a locally evolved race that has overcome previously effective resistance genes. Once the analysis is complete, findings will be published through AHDB.
In general, when a wheat variety is resistant at both the seedling and adult plant stages, that resistance is typically due to what's known as “all-stage resistance” (ASR) genes. If what we’re seeing now is the breakdown of a specific ASR gene, such as Yr15, it’s possible that adult plant resistance may also be lost.
However, we can’t rule out the possibility that some of these varieties also carry additional adult plant resistance (APR) genes that could still kick in later in the season. Because breeders don’t routinely publish the genetic makeup of their varieties, it’s difficult to know for sure.
So, while we can’t yet predict how things will play out this season, there is still reason to be optimistic. With any luck, breeders will have stacked both ASR and APR genes into these varieties to provide more robust and lasting protection.
The good news is that, for now, this race still appears to be controlled by tebuconazole when used as an eradicant in spray programmes. However, the virulence of this new race, particularly the speed at which it produces successive spore generations, remains uncertain.
As a precaution, T1 and T2 spray programmes should aim to include both eradicant and protectant properties to safeguard the canopy. Additionally, intervals between applications should not exceed the recommended three to four weeks to ensure maximum efficacy.