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Tasteless sap puts pests off their greens

作者:太叔忡嘟    发布时间:2019-02-28 07:04:09    

By Andy Coghlan SAP-SUCKING aphids could soon lose their £100 million taste for cabbages, cauliflowers, sprouts, broccoli and other brassica. The cabbage aphid, Brevicoryne brassicae, spoils an estimated £100 million of vegetable crops in Britain each year, despite the use of powerful pesticides by farmers. Now researchers in Britain have identified a wild relative of these crops that resists the aphid. The wild relative, which grows in Mediterranean countries, makes a protein that puts the aphids off their food. The researchers hope to transfer this trait to crops, either through conventional breeding or genetic engineering. The wild relative, Brassica fruticulosa, is edible and should therefore produce edible hybrids if crossed with commercial crops. Bob Ellis and Rosemary Cole of Horticulture Research International, a group of independent research institutes, have already crossed B. fruticulosa with a commercial strain of broccoli. Later this year they hope to find out whether the hybrid is resistant to aphids. Ellis and Cole, based at HRI’s central laboratories in Wellesbourne, Warwickshire, have traced the plant’s resistance to a protein which appears to work by blocking the aphid’s taste receptors. Because it cannot taste any sap, the insect concludes that it has landed on an inedible plant and flies away. The taste-killing compound is a protein called a lectin, which is produced in large quantities by B. fruticulosa. “We think it binds to receptors in the aphids’ foreguts and prevents the insects from tasting the sap to make sure it’s the right sort of plant,” Cole says. The researchers are now hunting the gene that makes it. If they locate the gene, they may be able to transfer it directly into crops by genetic engineering They are confident that the resistance gene will pose no danger to consumers, because people in areas where B. fruticulosa grows garnish their salads with leaves from the plant. “It’s one of the most commonly collected wild food plants in the Mediterranean,” says Ellis. Cole and Ellis began their research by looking for natural resistance to aphids in commercial varieties of brassica. Having met with little success, they turned to wild species. It soon became clear that aphids avoided B. fruticulosa. “We noticed that fewer aphids colonised it in the field, and those that did fared very badly indeed,” says Ellis. Cole conducted delicate experiments in which she wired aphids feeding on plants into electrical circuits via gold filaments as thin as human hairs. Changes in the electrical resistance of aphids coincides with different stages of their feeding cycle. “Aphids have stylets like flexible hypodermic syringes which they use to penetrate down into the plant and suck sap out,” explains Cole. From changes in their electrical resistance, she discovered that the insects stopped trying to feed on B. fruticulosa at the point where they first sampled the sap. Instead of sucking the sap for five hours the aphids withdrew their stylets. Despite their progress,

 

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