VIEW ARTICLE

Phytophthora megasperma var. sojae: Development of Wild-Type Strains for Genetic Research. Margaret Long, Staff Research Associate, Department of Plant Pathology, University of California, Riverside 92502; N. T. Keen(2), O. K. Ribeiro(3), J. V. Leary(4), D. C. Erwin(5), and G. A. Zentmyer(6). (2)(3)(4)(5)(6)Associate Professor, Postgraduate Research Associate, Assistant Professor, and Professors, respectively, Department of Plant Pathology, University of California, Riverside 92502. Phytopathology 65:592-597. Accepted for publication 18 December 1974. DOI: 10.1094/Phyto-65-592.

Single oospore and zoospore progeny of four field isolates representing three races of the soybean pathogen Phytophthora megasperma var. sojae exhibited great variability in pathogenicity, growth rates, and colony morphology. To obtain lines suitable for genetic research, the field isolates were repeatedly selfed (self-fertilized) and single oospore progeny were selected for high aggressivity, good zoospore and oospore production, and germinability, high growth rates, and typical colony morphology. Fifth generation (S₅) inbred lines were obtained that bred true for the above characters when either single zoospores or single oospores were cultured. Techniques were developed for the production of zoospores in sufficient numbers for mutagenesis, and a water-soaking method was used to obtain 50% germination of oospores. The inbred S₅ progeny are considered to be wild-type lines and they offer the prospect of obtaining reliable auxotrophic strains for genetic studies with P. megasperma var. sojae.