Pathotype Structure of Phytophthora sojae with Cultivar Rotation in Soybeans

Phytophthora sojae is an oomycete that causes Phytophthora stem and root rot (PRR) of soybeans. The disease has traditionally been managed primarily by incorporating single gene resistance into commercial cultivars. Fourteen known resistant genes (Rps) confer resistance to P. sojae. However, the pathogen has the ability to develop new pathotypes (originally called races) that overcome these Rps genes and thus they become ineffective. This is known as pathotype (or race) shift. Durability of Rps resistance in the field has been estimated in 8-15 years. Alternatively, PRR can be managed using partial resistance (tolerance), which is a polygenic resistance that reduces disease and is effective against all pathotypes of the pathogen. It is considered more durable since it does not impose selection pressure on the pathogen.