Phytophthora root and stem (PRR) is caused by the soil-borne oomycete Phytophthora sojae. It is the second-most yield limiting soybean disease in Ohio (Carl Bradley, 2016 Extension Pathologist Survey, personal communication) and causes over 30 million bushels in yield reductions annually nationwide (Koenning and Wrather, 2010).
PRR is primarily controlled through genetic host resistance. One type of resistance is qualitative, which is controlled by a single resistance (Rps) genes. Qualitative resistance, though, is only effective against specific P. sojae isolates, placing selection pressure on the pathogen population to rapidly evolve and overcome the deployed resistance. For this reason, the widespread use of Rps genes has led to shifts in pathogen virulence. This increase in pathotype complexity has created the need for soybean cultivars with more durable resistance. One way to meet this need is to increase levels of partial resistance, a second type of resistance which is controlled by multiple genes and is effective against a wider range of isolates than Rps genes.
The overall goals of this project are to identify perfect markers and develop germplasm for partial resistance to P. sojae. In collaboration with the Dorrance laboratory, members of the McHale laboratory (see Karhoff, Rolling, and Vargas-Garcia) are currently:
Characterizing a major quantitative trait locus (QTL) on chromosome 18 for partial resistance to P. sojae
Validating genomic selection models