The Vh8 locus of a new gene-for-gene interaction between Venturia inaequalis and the wild apple Malus sieversii is closely linked to the Vh2 locus in Malus pumila R12740-7A.

• The wild apple (Malus sieversii) is a large-fruited species from Central Asia, which is used as a source of scab resistance in cultivar breeding.• Phytopathological tests with races ofVenturia inaequaliswere performed to differentiate scab-resistance genes inMalusas well as an avirulence gene in the pathogen.• A novel gene-for-gene interaction betweenV. inaequalisandMaluswas identified. The locus of the scab-resistance geneVh8is linked with, or possibly allelic to, that of theVh2gene inMalus pumilaRussian apple R12740-7A, at the lower end of linkage group 2 ofMalus. Race 8 isolate NZ188B.2 is compatible withVh8, suggesting the loss or modification of the complementaryAvrVh8gene, while isolate 1639 overcomes bothVh2andVh8, but is incompatible with at least one other gene not detected by any of the other race isolates tested.• Our research is the first to differentiate scab-resistance genes in a putative gene cluster in apple with the aid of races ofV. inaequalis.New Phytologist(2005)doi: 10.1111/j.1469-8137.2005.01395.x© New Phytologist(2005) [ABSTRACT FROM AUTHOR]