Stephanie Karhoff

Stephanie Karhoff
Graduate Student
306A Kottman Hall, 2021 Coffey Rd., Columbus, Ohio 43210


BS, Agronomy, The Ohio State University

Project Description:  Characterization of QTL Associated with Partial Resistance to Phytophthora Stem and Root Rot

Phytophthora stem and root rot, caused by the soilborne oomycete Phytophthora sojae Kaufmann and Gerdemann, is a serious disease of soybeans [Glycine max (L.) Merr.].  Host resistance is a common management practice for this disease and race-specific dominant genes for resistance (Rps genes) have been incorporated into numerous commercial varieties.  However, the widespread deployment of Rps genes has led to a shift in physiological races of P. sojae.  Partial resistance is quantitatively inherited and effective against a wider range of races of P. sojae, resulting in a reduced level of root rot.  Due to its broad spectrum nature and the development of low levels of disease, partial resistance places less selection pressure on P. sojae populations and is theoretically more robust than Rps gene mediated resistance. Recently a major quantitative trait loci (QTL) was identified on chromosome 18 (8-16 cM), explaining 10-45% of phenotypic variance.  QTL of large effect are uncommon in partial resistance against P. sojae and it remain unknown if it represents a unique resistance mechanism.  My project aims to characterize this major QTL by determining its influence on disease resistance and overall agronomic performance, and by investigating the underlying genetic mechanism(s) controlling it.  Epistatic interactions will also be characterized by introgressing the QTL into a diverse range of elite cultivar backgrounds.


Karhoff S, Lee S, Mian MAR, Ralston TI, Niblack TL, Dorrance AE, McHale LK (2019) Phenotypic characterization of a major quantitative disease resistance locus for partial resistance to Phytophthora sojae. Crop Science. doi: 10.2135/cropsci2018.08.0514.