Host‐plants of Heterodera rostochiensis Woll. and the Breeding for Resistance 1)

The two most important aspects of the host‐parasite relation of the potato and the tomato versus Heterodera rostochiensis Woll. are discussed. Many transitory forms between very poor and good hosts have been found in wild and primitive forms of these crops. The nature and the mode of inheritance of forms are described and their consequences for breeding work discussed. Several patho‐types are found and it is argued that many more exist. Much variation has also been found in the amount of damage in good hosts when heavily attacked. Some varieties, both in potato and in tomato, have been found with a high degree of tolerance to damage.