This is the VOA Special English Agriculture Report.
Plant breeders and genetic engineers keep working to give crops the strength to resist threats like insects, diseases, droughts or floods.
But before you can resist a threat, you need to understand it.
We told you last week about a newly completed genetic map of the organism that causes late blight. That disease led to starvation in Ireland from potato shortages in the middle of the 1800s. The new genome could lead to better ways to protect potatoes, tomatoes and other crops.
Science may supply a stronger crop. Yet that does not always guarantee demand.
Nik Grunwald from the United States Agriculture Department worked on the international team that completed the genome. He says it is possible to grow potatoes that resist late blight. But these may not look like Russet potatoes. And most American farmers grow Russets because, as Nik Grunwald puts it, "that is where the demand is."
Another example of scientific progress involves a natural bacterium known as Bt. Bt is used as a pesticide to fight cotton bollworms, corn borers and other pests. Scientists have found a way to grow cotton plants that contain a Bt gene, reducing the need for pesticides. But sometimes, when one problem gets solved, another one appears.
In China, some farmers and researchers blame a decrease in pesticide use for an increase in pests unaffected by Bt. Also, there are concerns that some organisms could begin to resist the plants designed to resist them.
And scientists are reporting this week on what they call the "indirect costs" of a virus-resistance gene in Cucurbita. This is the species of squash that includes pumpkins and gourds. The scientists say virus-resistant transgenic squash are grown throughout the United States and much of Mexico.
The genetically engineered squash are usually larger and healthier than wild squash. But a three-year study showed that beetles like to feed more on the transgenic plants, increasing cases of wilt disease. The report by a team from the United States and China appears in the Proceedings of the National Academy of Sciences.
The researchers point out that gene flow between crops and their wild relatives is common and difficult to contain. They note concerns that wild plants could, as a result, gain genetically engineered resistances. And these could affect the natural balance in their environment.
And that's the VOA Special English Agriculture Report, written by Jerilyn Watson. I'm Bob Doughty.
genome: the total genetic content contained in a haploid set of chromosomes in eukaryotes, in a single chromosome in bacteria, or in the DNA or RNA of viruses 基因组
Russet potato: a large brown-skinned, white-fleshed variety of potato 褐色土豆
bacterium: any of the unicellular prokaryotic microorganisms of the class Schizomycetes, which vary in terms of morphology, oxygen and nutritional requirements, and motility, and may be free-living, saprophytic, or pathogenic in plants or animals 细菌
bollworm: any of various moth caterpillars that destroy cotton bolls 棉铃虫
corn borer: the larva of a European moth, now common in many areas of eastern North America, that feeds on and destroys corn and other plants, including potatoes and beans 一种吞食毁坏玉米作物的驻虫
gourd: any of several trailing or climbing plants related to the pumpkin, squash, and cucumber and bearing fruits with a hard rind 葫芦属植物
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（Source: VOA 英语点津编辑）