问题 问答题 简答题

举例植物病原物以什么状态、在什么场所越冬?并通过哪些途径传播到健康植物体?

答案

参考答案:

病原物有各种越夏或越冬的方式。如病原真菌,有的以侵染菌丝或休眠菌丝在受侵染的病株内越冬或越夏;有的可以以休眠体在植株内外存活;有的在病株残体和土壤中以腐生方式生活。病原细菌都可以在病株收获的种子、块茎和块根内越冬,有些可以在土壤中越冬,有的可以在昆虫体内或其他寄主植物上越冬;有些细菌虽然在土壤中不易成活,但若结成细菌团,或者存在于病残体中就能长期存在。专性寄生的真菌不能营腐生活,因此这类病原物大都在寄主体内越冬越夏,或以休眠的卵孢子在土壤或病残体越冬或越夏。

植物病原物的主要越冬场所大致有以下几个方面:田间病株;种子、苗木和其它繁殖材料;土壤;病株残体;肥料

阅读理解

阅读理解

      Where we live, on the eastern shore of Maryland, the gentle waters run in and out like fingers slimming at the tips.

     The Canada geese know this place, as do the white swans and the ducks.In autumn, they come home

for the winter.Once or twice each year, snow and frozen rain move into the area.When this happens, if the river is at its narrowest, there is a freeze which hardens the water to ice.

     One morning, a friend of mine set the breakfast table beside the huge window, which overlooked the

Tred Avon River.Suddenly she leaned forward and cried out, "There is a goose out there."

     We saw the figure of a large Canada goose, very still, its wings folded tight to its sides, its feet frozen

into the ice.

     Then from the dark skies, she saw a line of swans.They floated from the top of the sky downward

and at last landed on the ice.My friend was on her feet now, with one hand against her mouth, unbelieving.As the swans surrounded the frozen goose, she feared that life it still had might be pecked(啄) out by

those great swan bills.

     Instead, those bills began to work on the ice.The long necks were lifted and curved down, again and

again.It went on for a long time.At last, the goose's head was lifted.Its body was pulled.Then the goose

was free and stood on the ice.And the swans stood in the air watching.Then, as if it had cried, "I cannot

fly."Four of the swans came down around it.Their powerful beaks chipped off the ice held in the feathers.

Slowly, the goose spread its wings as far as they would go, and moved slowly into the sky.

     This is a true story.I just think of it in the bad moment, and from it comes only one hopeful question:If

so for birds, why not for man?

1. Which would be the best title for the passage?

A. Why Not for Man?   

B. Graceful Swans

C. Swans' Brave Act    

D. I Just Couldn't Believe It!

2. What happened to the Canada goose?

A. It was deserted by other geese.    

B. It was stuck in the ice.

C. It was wounded and couldn't fly.  

D. It was lost in the water.

3. At first the author's friend was worried that________.

A. the swans would not help the Canada goose

B. she didn't care about this matter any more

C. the swans wouldn't identify with the Canada goose

D. the swans would peck the Canada goose to death

4. What did the swans do when they saw the Canada goose couldn't fly?

A. They chipped off the ice held in its feathers.

B. They waited patiently for the ice held in its feathers to melt.

C. They came down and lifted it up to the sky together.

D. They stayed with it and protected it.

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