29 September 1995

Complicated eyespot poses bigger threat

BIG questions over straw management remain following the relatively recent discovery of a sexual stage of the eyespot fungus.

"We now know that eyespot is more complicated than we thought," said John Lucas of Long Ashton Research Station.

Until 1987, when the sexual form was first found in Australia, it was thought eyespot was a quite simple fungus, spread by rain-splashed asexual conidia over short distances.

Recent surveys of wheat stubbles in UK set-aside fields found sexual ascospores on nearly half the 45 sites examined. "So its widely distributed," said Mr Lucas. "Theres no doubt that the long-term persistence of straw on set-aside favours the formation of ascospores."

November to May

The findings mean airborne ascospores can infect surrounding crops at any time from November to May, he explained. But the conditions favouring their development are still unclear.

"The big questions are how far can they spread and what is their potential in the development of resistance?" The role of wild grasses in harbouring the sexual stage is also unknown.

Mr Lucas believes the genetic variation they bring is more important because it enables new resistance-breaking strains to develop.

Ascospore infection probably accounts for unexpectedly high levels of eyespot in supposedly unthreatened first wheats, according to ADAS pathologist Bill Clark.

That could change previous advice to leave wheat stubbles unploughed when sowing oilseed rape, he suggested. If left on the surface the straw could be acting as an eyespot reservoir for neighbouring fields.

New information on eyespot suggests a change in control strategies may be needed.