The effects on a population of potato-root eelworm (Heterodera rostochiensis) of growing potatoes resistant to pathotype B

The effects on a potato-root eelworm (Heterodera rostochiensis Woll.) population of growing potatoes resistant to pathotype B of the eelworm were investigated. The eelworm population, which was originally nearly entirely pathotype A, had been changed into a mixture of pathotypes A, B and C before 1961, when the experiments described in this paper began, by growing potatoes resistant only to pathotype A. The resistant potatoes grown in the years 1961 and 1962 were certain clones of the hybrid triploid species Solarium xjuzepczukii Buk., clones bred from S. multidissectum Hawkes with the gene H₂ and clones bred from S. vernei Bitt. et Wittm. In the years 1963-65 the clone used was D 40 which has both the gene H₂ from Andigena and the gene H₂ from 5. multidissectum and is resistant to both pathotypes A and B of the eelworm. The only potatoes which caused a reduction in the egg population were those bred from S. vernei. The clone D 40, although it had little effect on the egg population, appeared to have more resistance than could be accounted for from possessing genes H₁ and H₂.