VOA慢速英语-Development Report - Fighting Witchweed in African S

Scientists develop herbicide-resistant seeds that can kill the parasitic¹ plant. Transcript² of radio broadcast:
23 June 2008

This is the VOA Special English Development Report.
　

A sorghum3 field infested4 with striga, or witchweed

Farmers in Africa call the striga plant by the name witchweed. It grows a pleasant looking purple flower. But it attacks many crops in the grass family. Witchweed is among the few flowering weeds that act as parasites⁶ on other plants.

Every year it causes six to seven billion dollars in damage to African grain sorghum. Sorghum is important to the local food supply. The witchweed steals water and nutrients⁷ from the roots and attacks the sorghum with a poisonous substance.

Now, scientists say they have produced seeds that can protect sorghum crops from witchweed.

Kassim Al-Katib is a weed expert at Kansas State University in the United States. Mitch Tuinstra is a genetics and plant-breeding expert formerly⁸ at Kansas State but now at Purdue University in Indiana.

To deal with witchweed, they developed special sorghum-seed genes⁹. These genes can accept carefully chosen chemical herbicides without being harmed. The researchers placed the herbicides on the sorghum seeds. Kassim al-Katib said the seeds kill the witchweed as the sorghum grows.

Mitch Tuinstra directed greenhouse tests of the seeds in the Netherlands in two thousand five and two thousand six. Similar studies took place in field trials in Mali and Niger. These studies showed the treatment to be highly successful.

Mitch Tuinstra recently returned from Africa, where he met with agriculture experts. They are working to develop local kinds of sorghum that employ the genes. The project is a collective research program under the United States Agency for International Development.

Witchweed has another unusual quality. It requires chemical signals from sorghum seeds to grow. If no sorghum seeds are present, the witchweed seeds can lie under the soil for years. The seeds begin to grow only when they receive the needed chemical signals.

Witchweed seed capsules can hold four hundred to five hundred seeds. Winds and rain spread the parasite⁵. The plant can reduce a farmer's crop. Or it can completely destroy many hectares of grain. Witchweed is very difficult to remove after it invades an area.

Damage from the parasite is worst in dry soil with low fertility. It often strikes farmers who work the poorest land. This can mean disaster for people who already do not have enough to eat.

And that's the VOA Special English Development Report, written by Jerilyn Watson.

1 parasitic   

adj.寄生的

参考例句：

• Will global warming mean the spread of tropical parasitic diseases?全球变暖是否意味着热带寄生虫病会蔓延呢？
• By definition,this way of life is parasitic.从其含义来说，这是种寄生虫的生活方式。

2 transcript   

n.抄本，誊本，副本，肄业证书

参考例句：

• A transcript of the tapes was presented as evidence in court.一份录音带的文字本作为证据被呈交法庭。
• They wouldn't let me have a transcript of the interview.他们拒绝给我一份采访的文字整理稿。

3 sorghum   

n.高粱属的植物，高粱糖浆，甜得发腻的东西

参考例句：

• We can grow sorghum or maize on this plot.这块地可以种高粱或玉米。
• They made sorghum into pig feed.他们把高粱做成了猪饲料。

4 infested   

adj.为患的，大批滋生的（常与with搭配）v.害虫、野兽大批出没于( infest的过去式和过去分词 )；遍布于

参考例句：

• The kitchen was infested with ants. 厨房里到处是蚂蚁。
• The apartments were infested with rats and roaches. 公寓里面到处都是老鼠和蟑螂。

5 parasite   

n.寄生虫；寄生菌；食客

参考例句：

• The lazy man was a parasite on his family.那懒汉是家里的寄生虫。
• I don't want to be a parasite.I must earn my own way in life.我不想做寄生虫，我要自己养活自己。

6 parasites   

寄生物( parasite的名词复数 )； 靠他人为生的人； 诸虫

参考例句：

• These symptoms may be referable to virus infection rather than parasites. 这些症状也许是由病毒感染引起的，而与寄生虫无关。
• Kangaroos harbor a vast range of parasites. 袋鼠身上有各种各样的寄生虫。

7 nutrients   

n.（食品或化学品）营养物，营养品( nutrient的名词复数 )

参考例句：

• a lack of essential nutrients 基本营养的缺乏
• Nutrients are absorbed into the bloodstream. 营养素被吸收进血液。 来自《简明英汉词典》

8 formerly   

adv.从前，以前

参考例句：

• We now enjoy these comforts of which formerly we had only heard.我们现在享受到了过去只是听说过的那些舒适条件。
• This boat was formerly used on the rivers of China.这船从前航行在中国内河里。

9 genes   

n.基因( gene的名词复数 )

参考例句：

• You have good genes from your parents, so you should live a long time. 你从父母那儿获得优良的基因，所以能够活得很长。 来自《简明英汉词典》
• Differences will help to reveal the functions of the genes. 它们间的差异将会帮助我们揭开基因多种功能。 来自英汉非文学 - 生命科学 - 生物技术的世纪