DEVELOPMENT OF A DNA MARKER FOR V-M, A GENE CONFERRING RESISTANCE TO APPLE SCAB

Primers of arbitrary sequence were screened by bulked segregant analys is to identify DNA fragments linked to V-m, a gene conferring resistan ce to apple scab (Venturia inaequalis). A 687-bp fragment generated by 10-base primer OPE 12 gave tight linkage (no recombinants) in a popul ation of 59 individuals from the cross 'Empire' x NY74828-12. The DNA fragment was sequenced, and two specific primers were generated to pro duce a STS marker for V-m. These primers were used in New Zealand to s creen a second population of 180 individuals from a different cross. I n this population, the marker displayed 8% recombination with V-m. A s urvey of Malus germplasm indicated that the marker was present in rela tively few accessions, but was present in all known sources of V-m, in cluding the cultivar Murray. However, none of the other sources of sca b resistance, nor any other commercial cultivar, displayed the OPE 12 fragment. These results suggest that this marker should be useful for the pyramiding of scab resistance genes in cultivated apple and, perha ps, for identifying other accessions in the Malus germplasm collection that possess V-m.