MAPPING PHYTOPHTHORA RESISTANCE LOCI IN SOYBEAN WITH RESTRICTION-FRAGMENT-LENGTH-POLYMORPHISM MARKERS

Phytophthora root rot, caused by Phytophthora megasperma Drechs. f. sp. glycinea T. Kuan & D.C. Erwin, is one of the most serious diseases of soybean [Glycine max (L.) Merr.]. Six loci with alleles giving race-specific resistance of soybean to phytophthora have been reported. The first objective of this study was to map the phytophthora resistance (Rps) loci using restriction fragment length polymorphism (RFLP) markers. The second objective was to map the Rj2 locus for ineffective nodulation with RFLP markers, because of the linkage of Rj2 to Rps2. The mapping was conducted using a series of 'Williams' near-isogenic lines (NILs) with each having one or two phytophthora resistance alleles. The NILs were screened with 141 mapped RFLP markers. At least one polymorphism was found between each NIL and the recurrent parent. Linkage tests among the polymorphic RFLP markers, Rps loci, and the Rj2 locus were conducted using F2 populations. Linkage was found between RFLP markers and Rps1, Rps2, Rps3, Rps4, Rps5, and Rj2. Linkage was also found between Rps2 and Rj2.