| When growing in field, potato always happens that the stem on the ground becomes shorter and shorter, and leaves lose green color, all these cause under ground potatos getting much smaller, and make the quality and the yield per unit area decrease, at last lose the value of cultivation. It is called potato variety degeneration. It makes people feel puzzle till the three hypotheses are assumed, which are virus theory, ecology theory and senescence theory. It has been debated for a long time since then. With science and technology development, in 1955, scientists realized that it was virus, which caused potato degeneration.After experiments and investigations, there are more than 20 types of potato viruses being discovered, such as PVS, PVX, PVY, PSTVd, PLRV, PVA, PAMV, PVM, etc. Some potato virus cause symptoms known as 'spraing' consisting of brown arcs and circles in tubers of fresh potato, sometimes visible on the tuber surface also. Depending on the potato cultivar, other symptoms such as stunting of shoots and yellowing of leaves may develop. Infection by the virus causes quantitative yield loss, but the qualitative loss is more important. Once virus invades potato, it may live all the life in potato, and make yield decrease about 20-30% normally and more than 80% in severe case. If the situation develop to be worse, the potato will lose its value of being a potato seed.Since virus invasion causes potato degeneration, we have to create virus-free potato materials by experimental steps. To get the virus-free potato, we should perform in germfree condition through biology technology, and then obtain micro-potato without virus.We can get virus-free potato seed through the following measurements: First, buds of the potato tuber are induced and disinfected in door; then the meristem is cut...
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