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 out 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 American. 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 aliments. 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 from its lack of tolerance. The symptoms shown may cause an error in diagnosis, so that treatment may be directed toward bacteria which could be the result of a susceptibility caused by a primary virus infection. 1. How many diseases are known to attack wheat? A) Around 30,000 B) Around 140 C) Around 29,960 D) Around 40 2. According to this passage, which of the following would a plant disease result in if left unchecked? A) A world war. B) Border conflicts. C) Rations of grain and meat. D) Social upheavals. 3. What is the main idea of the second paragraph? A) Some plants have relative immunity to a great many diseases, while others have a susceptibility to them. B) The tolerance of a particular plant changes as the growing condition change. C) A blight killed virtually every chestnut tree in North American. D) A blight may be a national infection. 4. According to the passage, some plant diseases can be prevented by A) killing parasites. B) inoculation C) Killing insects D) improving growing conditions 5. Which of the following statements is not true? A) Some plant diseases may be caused by bacteria. B) Some plant diseases may be caused by pathogens. C) Some plant diseases may be caused by fungus. D) Symptoms are always helpful in identifying diseases. Keys: DDABD
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2017高考英语人教版一轮学案:选修七 Unit2 Robots
2017高考英语人教版一轮学案:必修二 Unit5 Music
2017届高考英语一轮复习顶尖学案:必修1 Unit 1 Lifestyles 生活方式(北师大版)
2017高考英语人教版一轮学案:必修五 Unit5 First aid
2017高考英语人教版一轮学案:选修七 Unit3 Under the sea
2017高考英语人教版一轮学案:必修二 Unit1 Cultural relics
2017高考英语人教版一轮学案:选修八 Unit4 Pygmalion
2017高考英语人教版一轮学案:选修六 Unit3 A healthy life
2017高考英语人教版一轮学案:必修三 Unit2 Healthy eating
2010届高三英语一轮复习必备精品同步练习:Module7 unit2
2017高考英语人教版一轮学案:必修四 Unit5 Theme parks
2017高考英语人教版一轮学案:必修三 Unit1 Festivals around the world
2017高考英语人教版一轮学案:必修五 Unit1 Great scientists
2017高考英语人教版一轮学案:选修八 Unit5 Meeting your ancestors
2017高考英语人教版一轮学案:必修一 Unit5 Nelson Mandela — a modern hero
2017高考英语人教版一轮学案:必修三 Unit3 The Million Pound Bank Note
2017届高考英语一轮复习顶尖学案:必修1 Unit 2 Heroes 英雄(北师大版)
2017高考英语人教版一轮学案:必修二 Unit4 Wildlife protection
2017高考英语人教版一轮学案:选修六 Unit2 Poems
2017高考英语人教版一轮学案:选修八 Unit1 A land of diversity
2017高考英语人教版一轮学案:必修一 Unit2 English around the world
2017高考英语人教版一轮学案:必修五 Unit4 Making the news
2010届高三英语一轮复习必备精品同步练习:Module7 unit3
2017高考英语人教版一轮学案:必修二 Unit2 The Olympic Games
2017届高考英语一轮复习顶尖学案:必修2 Unit 5 Rhythm 节奏(北师大版)
2017高考英语人教版一轮学案:必修四 Unit3 A taste of English humour
2017高考英语人教版一轮学案:选修六 Unit1 Art
2017高考英语人教版一轮学案:必修四 Unit1 Women of achievement