Mapping partial resistance to Pythium irregulare in the soybean accession PI 424354
M. L. ELLIS (1), P. A. Paul (2), S. K. St. Martin (3), A. E. Dorrance (2)
(1) Ohio State University, Wooster, OH, U.S.A.; (2) Ohio State University, OARDC, Wooster, OH, U.S.A.; (3) Ohio State University, Columbus, OH, U.S.A.
Phytopathology 101:S48

Pythium irregulare causes damping-off of soybean and has emerged as an important soybean seedling pathogen in Ohio. The objective of this research was to identify major quantitative trait loci (QTLs) in the plant introduction PI 424354 that confers resistance to P. irregulare. Two BC₁F_2:3 populations were used in this study including: 224 recombinant inbred lines (RILs) of OHS 303 (partially susceptible) x (Williams (susceptible) x PI 424354) and 128 RILs of Dennison (susceptible) x (Williams x PI 424354). Seeds from each RIL were planted into a colonized sand-cornmeal mixture. Data was collected from 2-week old seedlings for percent germination, total weight (g), root weight (g), and a root rot score using an ordinal scale. Based on the analysis of the phenotype data for both populations, there was a significant difference between lines (P < 0.0001) for root weight and root rot scores, and the data for both populations fit the model for quantitative resistance. A combination of SNP data from the BeadXpress and SSR will be used to construct the genetic map and identify the QTL(s). These results suggest that this soybean accession can be an important source of partial resistance in developing germplasm for breeding new cultivars with more durable resistance to P. irregulare.