本世纪20年代,美国东北部发现一种奇怪的马铃薯病,1962年在马里兰州一个农业研究中心工作的Raymer发现:引起这种马铃薯病的病原体也可以在蕃茄植株中生长,并在二周内引起典型的症状。受侵染的蕃茄叶子经磷酸盐提取后,在高达100000g的离心速度下,其有感染性的物质仍在提取物的上清中。上述结果表明,具有感染性的物质不是病毒,而是一种比病毒更小的病原体。Raymer立即意识到 In the 1920s, a strange potato disease was discovered in the northeastern United States. Raymer, who worked in a agricultural research center in Maryland in 1962, discovered that the pathogen causing the potato disease can also grow in tomato plants within two weeks. Causes typical symptoms. After ingested tomato leaves were extracted with phosphate, the infective material was still in the supernatant of the extract at a centrifugal speed of up to 100,000 g. The above results indicate that the infective substance is not a virus but a smaller pathogen than the virus. Raymer immediately realized