20 September 1996

Boost for nematode control

Edward Long

NEMATODE control could get a big boost soon, says a Scottish potato breeder who has developed varieties with resistance to the two highly damaging species.

Jack Dunnett of Caithness Potatoes believes that by planting varieties with partial resistance to Globodera pallida as well as full resistance against the G rostochiensis type, together with effective nematicides, growers will be able to deliver a knock-out blow to the pest. He is responsible for the first British-bred double resistor to reach the NIAB recommended list.

Until now there have been few varieties capable of resisting both species. On the NIABs recommended list for 1996 only the Dutch-bred Sante and Dr Dunnetts Nadine and Valor have the double-barrelled protection. But he has several other varieties in the development pipeline with similar characteristics.

In a crop planted with a susceptible variety a nematode population can easily multiply 40 to 50 times in a single season. "If nematicide kills 95% of the initial population the survivors need only multiply twentyfold to restore the original population."

Growers should aim to stop that by growing a resistant variety. Although the pest can multiply on such varieties, numbers do not rebuild enough for it to suffer a net loss.

In trials at Harper Adams College in Shropshire, where Valor was grown on nematicide-treated land, the initial egg population was knocked from 142/g of soil to 75 in the first year and to 18 in the second.

Three rotational cycles could eliminate the pest, says Dr Dunnett. &#42


&#8226 Hit nematodes hard with double resistors like Valor or Harmony plus nematicides.

&#8226 Three rotations could eliminate the problem.

&#8226 Valor – Cara-cross maincrop, uniform white skinned, oval tubers, good resistance to tuber blight, for pre-pack, late baker and general ware.

&#8226 Harmony – early maincrop in NIAB trials, good scab resistance, Nadine parentage but tuber dry matter about 1.5% better, baker-sized tubers with bright skins.


DOUBLE RESISTORS

Nail nematodes with dual resistance varieties like Harmony, plus nematicides, says Scottish potato breeder Jack Dunnett.