Potatoes infected by a viroid
These potatoes have been infected by the potato spindle tuber viroid (PSTV). It is typically spread when infected knives are used to cut healthy potatoes, which are then planted.
Source
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"OpenStax College, Other Acellular Entities: Prions and Viroids. October 16, 2013."
http://cnx.org/content/m44601/latest/Figure_21_04_02.jpg
OpenStax CNX
CC BY 3.0.
