问题 问答题 简答题

植物线虫所致病害有哪些特点?

答案

参考答案:

1、线虫以口针对寄主植物造成机械损伤外,主要是穿刺时分泌各种酶和毒素,引起植物的各种病变。不同属的线虫引起的植物病害田间表现症状差别很大。

2、主要症状有生长缓慢、衰弱、矮小、叶色失常、等类似营养不良现象;局部畸形,叶片干枯、扭曲、坏死,籽粒变成虫瘿等;根部出现根结、须根丛生、根部腐烂等。

3、诊断和线虫病害和鉴定线虫时,一般可在植物受害部位,特别是根结、种瘿内分离出线虫,然后进行镜检。

阅读理解

阅读理解

       Everyone has his own way of saying things and his own special expressions. Many American

everyday expressions are from colors.

       Red is a hot color. Americans often use it to express "heat". They may say they are red hot about

something unfair. When they're red hot they are very angry about something. Fast loud music is popular

with many people. They may say the music is red hot.

       Pink is a lighter kind of red. People sometimes say they're in the pink when they're in good health.

The expression was first used in America at the beginning of the 20th century. It probably came from

many babies who were born with a nice pink color showing good health.

       Blue is a cool color. The traditional blues music in the USA is the opposite of(与……相反) red

hot music. Blues is slow and sad.

       The color green is natural for trees and grass. But it's an unnatural color for humans. A person who

has a sick feeling stomach may say he feels a little green. A passenger on a boat who is feeling very sick

from high waves may look very green.

1. What does the expression "be red hot about" mean?

A. Be very angry.          

B. Be unfair.

C. Be happy.              

D. Be very popular.

2. Why do Americans use the color pink to express the meaning of healthy?

A. Because the color pink is lighter than the color red.

B. Because their ancestors(祖先) did so many years ago.

C. Because many healthy babies were born with the pink color.

D. Because it's a traditional expression.

3. What's the opposite of the red hot music?

A. Fast music.            

B. Loud music.

C. Blues music.            

D. Country music.

4. How many colors are mentioned in the passage?

A. 3.        

B. 4.        

C. 5.        

D. 6.

5. Which is the BEST title for the passage?

A. Different Colors

B. Strange Expressions

C. Colorful World

D. Feelings Behind Color Words

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