NEMATODE WORMS that devastate potato crops can be kept at bay by rotating
potatoes with genetically modified crops, say British researchers.
In badly infested fields, potato cyst nematodes can cut yields by up to 80
per cent. Eggs left in the soil the previous year hatch into larvae, which
burrow into the potato roots, scavenging nutrients and causing the plant to
wither and die. Females in the root swell up, eventually forming cysts
containing eggs, ready to continue the life cycle the following year.
Rotating potatoes with other crops should break the cycle. However, at
harvest some potatoes are always missed, and the next season they pop up as
weeds or 鈥渧olunteers鈥� among the new crop, perpetuating the worms鈥� life
cycle.
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According to Alan Dewar of the Institute of Arable Crops Research at Broom鈥檚
Barn in Suffolk, at least 20 per cent of sugar beet fields in Britain are
infested with volunteer potatoes. At present farmers control them with
herbicides such as clopyralid. But these often don鈥檛 act fast enough to prevent
the nematodes completing their life cycle.
Working with colleagues at the institute鈥檚 sister facility in Rothamsted,
Hertfordshire, Dewar showed that a better solution was to grow a GM crop that is
resistant to the broad-spectrum weedkiller glyphosate (Annals of Applied
Biology, vol 136, p 179). Sprayed onto four nematode-infested fields, this
herbicide destroyed the potato volunteers fast enough to starve the nematode
larvae before they could reproduce. 鈥淭he larvae are the vulnerable stage of the
life cycle,鈥� he says. The spray doesn鈥檛 harm the glyphosate-resistant GM
crop.
Two sprayings of glyphosate worked best, reducing the numbers of eggs in the
soil by between 28 and 38 per cent. The number of eggs in plots of GM beet
treated with conventional herbicides increased by at least 170 per cent.
