NIAB TAG is investigating the possibility of at least one new race of brown rust (Puccinia triticina) on UK winter wheat following this year’s severe disease epidemic.

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"Yellow rust (Puccinia striiformis) hit wheat hard from April until early June, and just when we thought the rusts had done their worst for the season, brown rust appeared in mid-June and developed explosively over a short period of just a few weeks in some areas," says Dr Rosemary Bayles, principal cereal pathologist at NIAB TAG.

Some varieties have shown signs of being more susceptible than expected, with samples received from many of the most highly-rated varieties for brown rust resistance. This suggests the emergence of one or more new races of the disease in the UK warns Dr Bayles.

"The last time we saw anything similar to this year was in 2007, with a steady flow of samples from March through to late July reflecting early and continued disease pressure. This year the samples received were concentrated between mid-June and mid-July, reflecting the later epidemic more typical of brown rust."

NIAB TAG pathologists are now analysing isolates from various resistant varieties to check for new races. Testing is most advanced on the winter wheat variety Stigg, resistance rating 9, and Dr Bayles confirms that an isolate collected in the field was able to overcome the variety’s resistance in seedling tests.

"Since Stigg has previously been resistant to UK isolates this is evidence that we are dealing with a new race on this variety. Further tests are in progress to fully identify the race and assess which other varieties may be at risk. We will issue further information on these varieties when testing is complete," says Dr Bayles.

NIAB TAG is also checking for possible yellow rust race changes following this season’s widespread epidemic in wheat and fears that some varieties may be less resistant that their current disease ratings would suggest.