Abstract
The potato cyst-eelworm probably evolved along with the potato and other Solanum species on the Andes plateau of South America. It is now an important potato pest in the United Kingdom, continental Europe and isolated places elsewhere. Against some field populations, a dominant gene from S. tuberosum sub-species andigena confers resistance on certain new commercial varieties of potatoes, but the expression of this resistance depends on the mechanism of sex determination in the eelworm.