8 March 1996

Early attacks from aliens?

EARLY blight outbreaks of recent seasons may be due to an increase of early stem blight caused by a change in the fungal population balance.

So says AgrEvos research plant pathologist Dr Janice Pittis. She believes the current blight fungus is not the same as that which caused the Irish famines 150 years ago.

"An immigrant strain with a different breeding pattern has arrived in Europe, possibly from South America," she says. "The original fungus spread to Europe from central Mexico. A second strain, first spotted in the late 1950s, arrived on this side of the Atlantic in the 1970s and is now in UK crops."

Sex and spores

Both produce spores asexually when in single strain populations, but when they are together sex can occur, explains Dr Pittis. The resulting spores survive on tubers in the soil.

"So growers need to check crops sooner for signs of trouble. The danger with stem blight is that spores can move two ways. They can either go up to foliage, or down to the soil to infect tubers at an early stage of development," she says. "This may explain why despite judicious use of tin-based fungicides at the end of the season to clean up lingering infection on dying foliage, tuber blight has been so prevalent recently."