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Abstract

Specificity of interactions between eight Lactuca species (L. saligna, L. virosa, L. altaica, L. dregeana, L. perennis, L. tenerrima, L. tatarica, L. viminea) and two related genera (Mycelis muralis, Chondrilla juncea) and seven Bremia lactucae isolates from Lactuca serriola was studied in 96 accessions. The 35 L. saligna accessions gave no evidence for race-specificity and a non-host resistance is expected. L. virosa (36 accessions) showed a highly various response. A substantial part of the studied sets expressed a race-specific resistance. L. altaica (one accession), which is closely related to L. serriola, was susceptible to all isolates used. L. dregeana (2 accessions) showed also a race-specific response. The accessions of L. perennis (7), L. tatarica (2) and L. viminea (1) were resistant. The susceptibility of L. tenerrima (3 accessions), which is related to L. perennis, is unexpected. In Mycelis muralis (8 accessions) very often a incomplete resistance was observed. Chondrilla juncea (1 accession) was resistant to all isolates used. It can be concluded that the genetic distances between species cannot be used as a prediction for resistance or susceptibility.