Recent experiences of breeding leaf mould resistant tomatoes

After the introduction, in 1961, of breeding lines of tomato with complete resistance to all races of Cladosporium fulvum known until then, it was found in 1963 that this resistance could be broken by the occurrence of new races. Resistance to the new races was shown to be also available and to be dependent on one dominant factor.Assumedly a new relation between host and parasite had occurred. Consequences for breeding are discussed.