| Authors: | Patzoldt, M.E., Grau, C.R., Stephens, P.A., Kurtzweil, N.C., Carlson, S.R., Diers, B.W. |
| Abstract: | Many soybean [Glycine max (L.) Merr.] genotypes that carry resistance to soybean cyst nematode (Heterodera glycines Ichinohe) (SCN) from plant introduction (PI) 88788 also carry resistance to brown stem rot (BSR) caused by the soilborne fungus Phialophora gregata (Allington & Chamberlain) W. Gams f. sp. sojae Kobayashi, Yamamoto, Negishi, and Ogoshi. The objectives of our research were to map and localize BSR resistance quantitative trait loci (QTL) from Bell, a BSR resistant cultivar with SCN resistance from PI 88788. Initial mapping was done with a population of 93 F4–derived lines developed from a cross between Bell and the SCN and BSR susceptible cultivar, Colfax. Lines were evaluated for BSR resistance in two field environments, a greenhouse, and with genetic markers from linkage group (LG) J. To confirm and further localize a resistance QTL, three near isogenic line (NIL) populations were created using an F4–derived line from the Bell x Colfax population. In the F4 population, markers on LG J were significantly (P < 0.001) associated with BSR resistance in both the field (R2 = 45%) and greenhouse (R2 = 51%). Data from the NIL populations indicates the QTL is near the closely linked markers 21E22.sp1, 21E22.sp2, and 35E22.sp1, which is the same genetic region where Rbs1, Rbs2, and Rbs3, the three named BSR resistance genes, were previously mapped. In addition, the genetic region is tightly linked to a previously identified SCN resistance QTL from PI 88788. These results explain why many SCN resistant cultivars also carry BSR resistance and should assist breeders when selecting for resistance to both diseases. |