问题 问答题 简答题

主要病征类型:

答案

参考答案:

(1)霉状物:病原真菌侵染植物后,其营养体和繁殖体在草坪草感病部位呈现各种颜色的霉状物。如霜霉、青霉、灰霉、黑霉、烟霉、赤霉等。如禾草霜霉病等。(2)粉状物:病原真菌侵染植物后,其营养体和繁殖体在草坪草感病部位呈现各种颜色的粉状物。如白粉、黑粉等。如危害剪股颖、狗牙根、羊茅、早熟禾、野牛草等主要禾草的白粉病所表现的白粉状物,剪股颖、早熟禾的黑粉病在发病后期表现的黑粉。(3)锈状物:病原真菌在草坪草病部产生的黄褐色或铁锈色点状、块状、毛状或朵状物。如锈病。(4)点(粒)状物:病原真菌在草坪草感病部位的表皮组织下或突破寄主组织产生黑色(主要)、褐色或橘红色粒状物,即病菌的繁殖体。如温带禾草的炭疽病的黑色点状物。(5)线(丝)状物:草坪草感病部位产生的线(丝)状物,即菌索。如剪股颖、羊茅、黑麦草、早熟禾等的白绢病病部形成的颗粒状物。(6)脓状物(溢脓):病原细菌在草坪草感病部位出现脓状黏液,干燥后为胶质的粒状物或小块状物,这是细菌性病害特有的病征。如细菌性萎蔫病病部的溢脓。

单项选择题
单项选择题

Marriage, and its many ups and downs, still exercises a powerful hold over newspapers, magazines and the airwaves. Nearly 23m Americans watched Prince William being joined in holy marriage to Kate Middleton. Millions more have indulged in the break-up of Arnold Schwarzenegger’s marriage after revelations that he fathered a son with a maid.

Less delightful are revelations about the sorry state of marriage across the United States. Data from the Census Bureau show that married couples, for the first time, now make up less than half of all households.

The iconic American family, with mom, dad and kids under one roof, is fading. In every state the numbers of unmarried couples, childless households and single-person households are growing faster than those comprised of married people with children, finds the 2010 census. And the trend has a potent class dimension. Traditional marriage has evolved from a near-universal ritual to a luxury for the educated and affluent.

There barely was a marriage gap in 1960: only four percentage points separated the wedded ways of college and high-school graduates(76% versus 72%). The gap has since widened to 16 percentage points, according to the Pew Research Centre.

"Marriage has become much more selective, and that’s why the divorce rate has come down," said Bradford Wilcox, director of the National Marriage Project at the University of Virginia in Charlottesville. The project found that divorce rates for couples with college degrees are only a third as high as for those with a high-school degree.

Americans with a high-school degree or less tell researchers they would like to marry, but do not believe they can afford it. Instead, they raise children out of wedlock. Only 6% of children born to college-educated mothers were born outside marriage, according to the National Marriage Project. That compares with 44% of babies born to mothers whose education ended with high school.

"Less marriage means less income and more poverty," reckons Isabel Sawhill, a senior fellow at the Brookings Institution. She and other researchers have linked as much as half of the income inequality in America to changes in family composition: single-parent families (mostly those with a high-school degree or less) are getting poorer while married couples (with educations and dual incomes) are increasingly well-off. "This is a striking gap that is not well understood by the public," she says.

Do not expect the Democratic Party, however, to make an issue of the marriage gap in next year’s elections. Unmarried women voted overwhelmingly for Barack Obama. "You don’t want to suggest to someone who isn’t married and has children that they should be married," says Ms Sawhill. "That is a scorn on their lifestyle.\

According to the text, traditional marriage ().

A.is no longer considered holy and meaningful

B.is doomed to be replaced by new forms

C.tends to be kept by the wealthy and cultivated

D.enables couples to be loyal to each other