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

Abstract

The genetic map of Bremia lactucae was expanded utilizing 97 F1 progeny derived from a cross between Finnish and Californian isolates (SF5 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 B2 type and the homozygous recessive genotype determined the B1 type. 2003 Elsevier Science (USA). All rights reserved.