Wheat variety resistance could still halt yellow rust infection

Wheat growers are advised to check crops for yellow rust, following widespread reports of infection in crops, but be aware that many crops could still develop adult plant resistance.

The HGCA-funded UK Cereal Pathogen Virulence Survey has received many samples of very active wheat yellow rust over the winter. Varieties being tested include Gallant, Horatio, JB Diego, KWS Kielder, KWS Santiago and Solstice.

NIAB’s Dr Jane Thomas explains that yellow rust will remain viable over the winter in plants, and only dies if temperatures are low enough to kill the leaves which are infected. Otherwise the growth of the fungus either slows down or it remains dormant in the leaf until warmer conditions arrive.

“With continuing mild weather the risk remains that an early epidemic will develop in the spring, and fungicide programmes will need to be targeted for high risk situations,” advises Dr Thomas. Some crops with active rust were treated before Christmas but the continuing wet weather and waterlogged fields will delay any further spraying.

However, though autumn and winter infection has been spotted on a number of varieties, not all of these will remain at risk as the season progresses and adult plant resistance factors develop. Some varieties are only susceptible to infection at the seedling stage and become more resistant after stem extension to the currently known rust races.

“Updates on seedling reactions to the common ‘Warrior type’ races for varieties on the 2014/15 RL are now available based on UKCPVS testing last year,” says Dr Thomas. This information is summarised in Table 1 (also see attachment).

While the adult plant rating from the RL should guide fungicide programmes, growers should be aware that seedling infection may be seen on Chilton, Monterey and Leeds (all moderately resistant as adult plants) and KWS Croft and Myriad (both resistant as adult plants). Delphi, Revelation and Relay were susceptible to some, but not all, of the Warrior races used in testing but all have very good adult plant resistance. Cougar, KWS Gator and Dickens were resistant as seedlings and have very good adult plant resistance.

HGCA’s Dr Jenna Watts explains that since the RL disease ratings are based on information from the previous cropping season all varieties need to be monitored. “New races can develop through the season so be prepared to take action to protect crops in the early spring if infection is found.”

From spring 2014 HGCA will be doing regular disease monitoring on a small set of untreated trials in England and Scotland. This monitoring activity, in conjunction with UKCPVS, will help to quickly identify the development of any new rust races. The HGCA Information Sheet 26 Fungicide Activity and Performance in Wheat, which compares the activity of fungicides against yellow rust, has been updated.

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