Management of Phytophthora sojae of soybean: a review and future perspectives

Phytophthora sojae Kaufmann & Gerdemann has been a yield limiting factor for more than 60years on soybean (Glycine max L.) in Ohio and other regions where soils are poorly drained. Soybean is the primary host, although numerous Lupinus spp. have been shown to be infected based on artificial inoculations. More than 20 different major resistance (Rps) genes have been reported from sources from China, Japan and South Korea but few are deployed in cultivars. As in other host-pathogen systems with a gene-for-gene interaction, there are also numerous pathotypes (races) of P. sojae, with as few as 1 to more than 50 characterized within a single field. Due to high pathogen diversity and complexity in relation to pathotype, quantitative disease resistance (QDR) or partial resistance has become a priority and serves as the backbone for disease management in some production regions. However, QDR requires the use of seed treatments for early season protection in highly favourable environments. Current research efforts for the development of more durable management of this disease include the identification and characterization of novel Rps genes as well as markers and mechanisms that contribute to the expression of QDR. There are now two new seed treatment chemistries, ethaboxam and oxathiapiprolin, with efficacy towards P. sojae in addition to metalaxyl-based fungicides. Finally, pathogen population structure, both within and between production regions, as well as variability within Avr loci of P. sojae, are also elucidating potential new approaches to managing this disease.