1, The genes of viroid or defect-virus get into the animal cells together with virus and then replicate and function in the cell.

2, So far, more than 30 viruses or viroid were found on potato, and the virus diseases restrict the potato producing.

3, Viroid is small and exists less in host, which is difficult to purify.

4, As to the prevention and control of viroid diseases, there haven't been any leads to solve this in the world as yet.

5, Potato spindle tuber viroid (PSTV) in different parts of tubers of potato cv. "Tiger Head" was determined, by return electrophoresis with silver staining.

6, Rapid and accurate detection of the kinds and amount of virus and viroid in potato plants is an effective method to control potato diseases and pests.

7, The information replication of PSTV RNA not only refers to the theo refical problem of the molecular biology of PSTV RNA, but also the molecular basis of controlling viroid diseases.