Inheritance of Avirulence Factors andRestriction Fragment Length Polymorphism Markersin Outcrosses of the Oomycete Phytophthora sojae. Brett M. Tyler . Department of Plant Pathology, University of California, Davis 95616, and department of Plant Pathology, University of California, Riverside 92521-0122 U.S.A. Helga Forster(2), and Michael D. Coffey(2). (1) Department of Plant Pathology, University of California, Davis 95616, (2) department of Plant Pathology, University of California, Riverside 92521-0122 U.S.A. MPMI 8:515-523. Accepted 14 April 1995. Copyright 1995 The American Phytopathological Society.

F1 hybrids from crosses or three P. sojae isolates (P6497, P7064, and P7076) were identified by random amplified polymorphic DNA (RAPD) markers specific for each parent. The race types of the isolates were similar to races 2, 7, and 19, respectively. The hybrid nature of the progeny was confirmed by restriction fragment length polymorphisms (RFLPs). Selected F1 progeny were selfed to produce F2 progeny. RAPD and RFLP markers segregated in regular Mendelian fashion among one set of F2 progeny (from P6497 x P7064), but considerable bias in the transmission of markers was observed among F2 progeny from the second cross (P6497 x P7076). Specific avirulence in the pathogen against soybean resistance genes (Rps genes) was confirmed to be dominant in six cases tested (Rpsla, Rpslb, Rpslc, Rpsld, Rpslk, and Rps3a) and appeared to be dominant or semidominant in four others (Rps3b, Rps3c, Rps4, and Rps6). The segregation of avirulence among the F2 progeny supported the presence of single dominant avirulence genes (Avrla, Avrlb, and Avr3a) in the pathogen, matching three Rps genes (Rpsla, Rpslb, and Rps3a), and was consistent with the possible presence of two others (matching Rpslk and Rpsld). Genetic linkage was observed between some pairs of RFLP markers and between an RFLP marker and Avrlb.