AGRICULTURE REPORT - Audience Mail: A Maize Mystery for AGRI

AGRICULTURE REPORT - Audience Mail: A Maize¹ Mystery for AGRICULTURE REPORT
By Mario Ritter

Broadcast: Tuesday, April 26, 2005

I'm Gwen Out with the VOA Special English Agriculture Report.

 
 
A listener in Vietnam has a question about corn breeding. Ho Lan Phuong has read about "pure-line development" and "broad-line development." She wants to know the difference.

Since ancient times, farmers have chosen the best examples from each crop to provide seed for the next year. This method is called mass selection. It may be what our listener has seen described as broad-line development. Mass selection produces plants with similar genetic² qualities over time.

The pure-line method of breeding is similar. But it is more systematic³. In pure-line breeding, the best plants are chosen from a crop that has many different genetic qualities.

The seeds from these plants are grown. Then the best plants are chosen from the new crop. This process can go on for many years, until the seeds produce plants with measurable similarities and desirable qualities. Seed companies may use this method to produce seed for some crops.

But the pure-line method is not often used with widely traded crops. Today major crops like corn or wheat are developed as hybrids⁵.

About one hundred years ago, a scientist in the United States, G.H. Shull, made important discoveries about corn hybrids.

He mated corn with itself. Corn does not normally fertilize⁶ itself in nature. If corn is inbred, the seeds will produce a plant that clearly shows the qualities of the parent. But this inbreeding does not produce a strong plant.

Shull found that if he mated two inbred corn plants, they would produce a strong line with the good qualities of the parent plants. This is called crossbreeding.

Researchers soon recognized that they could crossbreed four inbred lines of corn. This "double cross" results in stronger corn with the best qualities of the parent plants. This is the way most hybrid⁴ corn is developed.

Modern hybrid corn produces much more grain than its ancestors. But success can create its own problems. For example, there is very little genetic difference in the corn grown across the United States. Experts estimate that current hybrids use less than five percent of the genetic diversity that exists.

There is a project called Germplasm Enhancement of Maize, or GEM⁷. It is a cooperative effort to increase the genetic diversity in corn. The project involves the Department of Agriculture, sixteen universities and twenty international companies.

This VOA Special English Agriculture Report was written by Mario Ritter. I'm Gwen Outen.

1 maize   

n.玉米

参考例句：

• There's a field planted with maize behind the house.房子后面有一块玉米地。
• We can grow sorghum or maize on this plot.这块地可以种高粱或玉米。

2 genetic   

adj.遗传的，遗传学的

参考例句：

• It's very difficult to treat genetic diseases.遗传性疾病治疗起来很困难。
• Each daughter cell can receive a full complement of the genetic information.每个子细胞可以收到遗传信息的一个完全补偿物。

3 systematic   

adj.有系统的，有计划的，有方法的

参考例句：

• The way he works isn't very systematic.他的工作不是很有条理。
• The teacher made a systematic work of teaching.这个教师进行系统的教学工作。

4 hybrid   

n.(动，植）杂种，混合物

参考例句：

• That is a hybrid perpetual rose.那是一株杂交的四季开花的蔷薇。
• The hybrid was tall,handsome,and intelligent.那混血儿高大、英俊、又聪明。

5 hybrids   

n.杂交生成的生物体( hybrid的名词复数 )；杂交植物（或动物）；杂种；（不同事物的）混合物

参考例句：

• All these brightly coloured hybrids are so lovely in the garden. 花园里所有这些色彩鲜艳的杂交花真美丽。 来自辞典例句
• The notion that interspecific hybrids are rare is ill-founded. 有一种看法认为种间杂种是罕见的，这种看法是无根据的。 来自辞典例句

6 fertilize   

v.使受精，施肥于，使肥沃

参考例句：

• Fertilizer is a substance put on land to fertilize it.肥料是施在地里使之肥沃的物质。
• Reading will fertilize his vocabulary.阅读会丰富他的词汇。

7 gem   

n.宝石，珠宝；受爱戴的人 [同]jewel

参考例句：

• The gem is beyond my pocket.这颗宝石我可买不起。
• The little gem is worth two thousand dollars.这块小宝石价值两千美元。