A genetic map of the lettuce downy mildew pathogen, Bremia lactucae, constructed from molecular markers and avirulence genes

The genetic map of Bremia lactucae was expanded utilizing 97 F-1 progeny derived from a cross between Finnish and Californian isolates (SF5 x C82P24). Genetic maps were constructed for each parent utilizing 7 avirulence genes, 83 RFLP markers, and 347 AFLP markers, and a consensus map was constructed from the complete data set. The framework map for SF5 contained 24 linkage groups distributed over 835 cM; the map for C82P24 contained 21 linkage groups distributed over 606 cM. The consensus map contained 12 linkage groups with markers from both parents and 24 parent-specific groups. Six avirulence genes mapped to different linkage groups; four were located at the ends of linkage groups. The closest linkages between molecular markers and avirulence genes were 3 cM to Avr4 and 1 cM to Avr7. Mating type seemed to be determined by a single locus, where the heterozygote determined the B-2 type and the homozygous recessive genotype determined the B-1 type. (C) 2003 Elsevier Science (USA). All rights reserved.