更多"Diseases of Agricultural Plants Pl"的相关试题:
[单项选择] Diseases of Agricultural Plants
Plants, like animals, are subject to diseases of various kinds. It has been estimated that some 30,000 different diseases attack our economic plants; forty are known to attack com, and about as many attack wheat. The results of unchecked plant disease are all too obvious in countries which have marginal food supplies. The problem will soon be more widespread as the population of the world increases at its frightening rate. Even in countries which are now amply fed by their agricultural products there could soon be critical food shortages. It is easy to imagine the consequences of some disastrous attack on one of the major crops; the resulting famines could kill millions of people, and the resulting hardship on other millions could cause political upheavals disastrous to the order of the world.
Some plants have relative immunity to a great many diseases, while others have a susceptibility to them. The tolerance of a part
A. A world war.
B. Border conflicts.
C. Rations of grain and meat.
D. Social upheavals.
[单项选择]
Diseases of Agricultural
Plants
Plants, like animals, are subject to
diseases of various kinds. It has been estimated that some 30,000 different
diseases attack our economic plants; forty are known to attack corn, and about
as many attack wheat. The results of unchecked plant disease are all too obvious
in countries which have marginal food supplies. The problem will soon be more
widespread as the population of the world increases at its frightening rate.
Even in countries which are now amply fed by their agricultural products there
could soon be critical food shortages. It is easy to imagine the consequences of
some disastrous attack on one of the major crops; the resulting famines could
kill millions of people, and the resulting hardship on other millions could
cause political upheavals disastrous to the order of the world.
Some plants have relative immunity to a great many diseases, while others have a
susceptibility to them. The tolerance of a particular plant changes as the
growing conditions change. A blight may be but a local infection easily
controlled; on the other hand it can attack particular plants in a whole region
or nation. An example is the blight which killed virtually every chestnut tree
in North America. Another is the famous potato blight in Ireland in the last
century. As a result of that, it was estimated that one million people died of
starvation and related ailments.
Plant pathologists have made
remarkable strides in identifying the pathogens of the various diseases.
Bacteria may invade a plant through an infestation of insect parasites carrying
the pathogen. A plant can also be inoculated by man. Other diseases might be
caused by fungus which attacks the plant in the form of a mold or smut or rust.
Frequently such a primary infection will weaken the plant so that a secondary
infection may result from9 its lack of tolerance. The symptoms shown may cause
an error in diagnosis10, so that treatment may be directed toward bacteria which
could be the result of a susceptibility caused by a primary virus
infection.How many diseases are known to attack wheat
A. Around 30,000.
B. Around 140.
C. Around 29,960.
D. Around 40.
[单项选择]
Diseases of Agricultural Plants
Plants, like animals, are subject to diseases of various kinds. It has been estimated that some 30,000 different diseases attack our economic plants; forty are known to attack com, and about as many attack wheat. The results of unchecked plant disease are all too obvious in countries which have marginal food supplies. The problem will soon be more widespread as the population of the world increases at its frightening rate. Even in countries which are now amply fed by their agricultural products there could soon be critical food shortages. It is easy to imagine the consequences of some disastrous attack on one of the major crops; the resulting famines could kill millions of people, and the resulting hardship on other millions could cause political upheavals disastrous to the order of the world.
Some plants have relative immunity to a great many diseases, while others have a susceptibility to them. The tolerance of a particular
A. Around 30,000.
B. Around 140.
C. Around 29,960.
D. Around 40.
[单项选择]
Plants in Desert
Only special plants can survive the terrible climate of a desert, for these are regions when the annual range of the soil temperature can be over 75℃. Furthermore, during the summer there are few clouds in the sky to protect plans from the sun’ s ray. Another problem is the fact that there are frequently strong winds that drive small, sharp particles of sand into the plants,earing and damaging them. The most difficult probiem for all forms of plant life, however, is the fact that the entire annual rainfall occurs during a few days or weeks in spring.
Grasses and flowers in desert survive from one year to the next by existing through the long, hot, dry season in the form of seeds. These seeds remain inactive unless the fight amount of’rain falls. If no rain falls, or if insufficient rain falls, they wait until the next year, or even still the next. Another factor that helps these plants to survive is the fact that their life cycl
A. Right
B. Wrong
C. Not mentioned
