22 November 1996

Fast way to tell nematode species apart

A NEW quick test to distinguish between cyst nematode species could help more potato growers avoid eelworm damage, according to a Scottish researcher.

Too many producers requesting soil tests for the pests fail to ask for the species to be identified, says SAC entomologist Andy Evans. But knowing which of the two key types – Globodera rostochiensis and G pallida – are present is vital in choosing varieties, he maintains.

The latter, which is harder to control, poses an increasing threat in Scotland as growers concentrate on varieties like Maris Piper, which are resistant to G rostochiensis, he says. "They are in effect selecting for pallida.

"The problem in the past was that to tell the two apart was labour intensive and involved breaking open the cysts and measuring the length of the mouth parts. That was always a drawback because it meant the test was prohibitively expensive."

DNA probes

Now a technique based on DNA probes developed by the Scottish Agricultural Science Agency allows testers to rapidly spot the molecular fingerprints left by each type.

"It means we can potentially do 48 samples at a time in the same time that it used to take to test just one or two," says Dr Evans.

Producers not taking advantage of the test and growing a G pallida-susceptible variety, like Maris Piper, on infected soil may not immediately notice a problem, he warns. "But they are allowing the problem to build up, so that all of a sudden they get hit next time they try to grow a susceptible type.

"If you have got pallida then varieties like Sante wont suffer so much yield loss and will lower the rate of nematode multiplication. But there are no varieties fully resistant to pallida yet available."

The new SAC species test costs about a third less than the original £45 test and the results are available within seven to 10 days, claims Dr Evans. "This is a considerable improvement and compares favourably if not better with species tests available in England."

Best strategy, he suggests, is for growers to arrange to have fields within potato rotations species tested at least once in every 10 years. &#42