A potato infected with root-knot nematode (left)
and a healthy potato. Click the image for more information about
Wild Potatoes Tapped for Nematode
Defense By Jan
March 23, 2004
Wild potatoes growing high above the desert in southeastern
Arizona may hold the genetic keys to a defense against the Columbia root-knot
nematode, according to Agricultural Research
The tiny, wormlike pest is especially troublesome in Washington,
Oregon and Idaho, where more than half of the U.S. tuber crop is grown. Growers
fumigate fields to keep the nematode from damaging the crop's roots. Annually,
they'll spend $20 million on fumigants to prevent crop losses of $40 million.
Since resistance isn't found in U.S. potatoes, ARS scientists
Chuck Brown and John Bamberg sought to fortify the crop with useful new genes
from its wild mountain relatives, including Solanum fendleri, a native
of the U.S. Southwest and northern Mexico. Bamberg manages S. fendleri
seedlots at the ARS
Genebank in Sturgeon Bay, Wis. Early tests in Prosser, Wash., showed some
specimens were nematode resistant.
The researchers decided to repeat the tests. But first, they
wished to see for themselves where the seed they had used originally came from,
collect new specimens and answer the question: "Why would a wild potato be
resistant to an agricultural pest?" In September 2002, this interest took them
to the Huachuca and Chiricahua mountains in Arizona. There, they collected
small tubers and seed from natural stands of S. fendleri at two sites at
altitudes of 6,000-8,000 feet.
Upon returning, they grew new plants from the seed and tubers
they had collected. Later, they assessed the nematode resistance or
susceptibility, observing that some individuals from the collection were good
hosts (susceptible), while others were not, meaning they resisted the pest.
Crossing the resistant S. fendleri plants with cultivated
potatoes, however, is difficult to do because of chromosome number differences.
Brown, at the ARS Vegetable and
Forage Crops Research Unit in Prosser, tackled this hurdle using a breeding
technique called "bridging crosses." The resulting plants are now growing in a
greenhouse, and Brown plans to cross them with cultivated sources, setting the
stage for breeders to develop new, nematode-resistant commercial varieties.
ARS is the U.S. Department of
Agriculture's chief scientific research agency.