马铃薯主要是靠块茎繁殖的作物。在长期的种植过程中，马铃薯容易受病毒侵染，且病毒通过块茎代代相传不断积累，造成马铃薯种性退化。如云南省大面积种植的马铃薯品种求拉，引入初期，产量较高，单个薯块较大，薯形较好；但是，现在的米拉品种，产量越来越低，薯块越来越小， Potatoes are mainly crops that multiply by tubers. In the long-term planting process, the potato is susceptible to virus infection, and the virus accumulates continuously through the tubers from generation to generation, causing the potato to degenerate. For example, the potato varieties planted in a large area in Yunnan Province were pulled in early stage, with higher yield, larger individual potato pieces and better potato shape. However, the current varieties of Mira are getting lower and lower and the potato pieces are getting smaller and smaller ,