Phytophthora sojae Avirulence Genes, RAPD, and RFLP Markers Used to Construct a Detailed Genetic Linkage Map. S. C. Whisson . Cooperative Research Centre for Tropical Plant Pathology, The University of Queensland, Brisbane 4072, Queensland, Australia. A. Drenth, D. J. Maclean, and J. A. G. Irwin. Cooperative Research Centre for Tropical Plant Pathology, The University of Queensland, Brisbane 4072, Queensland, Australia. MPMI 8:988-995. Accepted 28 August 1995. Copyright 1995 The American Phytopathological Society.

Two crosses between different races of Phytophthora sojae were established using one race as a common parent in both crosses. F2 populations comprising over 200 individuals were generated for each cross. A subset of 53 F2 individuals from each cross was selected at random for genetic analysis of virulence/avirulence and molecular markers, and finally the construction of a detailed genetic linkage map. The linkage map developed for P. sojae is based on a total of 257 markers (22 RFLP, 228 RAPD, and 7 avirulence genes). The linkage map comprises 10 major and 12 minor linkage groups covering a total of 830.5 cM. Close linkage was observed between Avr4 and Avr6 (0.0 cM), Avrlb and Avrlk (0.0 cM), and Avr3a and Avr5 (4.6 cM). Coupling phase linkage of RFLP and RAPD markers to all seven avirulence genes was identified at the minimum and maximum distances of 0.0 and 14.7 cM, respectively.