Genetic mapping of QTLs underlying partial Sclerotinia stem rot resistance in soybean

Sclerotinia stem rot, caused by Sclerotinia sclerotiorum, is an important yield reducing disease of soybean in the Midwestern states of the U.S. The objective of my study was to identify quantitative trait loci (QTLs) associated with partial Sclerotinia stem rot resistance in soybean plant introduction (PI) 391589B and Asgrow 2506.; The PI 3915898 with partial Sclerotinia stem rot resistance was crossed with a susceptible cultivar IA 2053 to develop a mapping population of 94 F2 derived lines. The population was evaluated for Sclerotinia stem rot resistance in the field in 2003 and 2004 and in the greenhouse in 2005. The population was also evaluated for genotypes with 109 polymorphic simple sequence repeat (SSR) markers. Both single marker analysis (SMA) and composite interval mapping (CIM) methods were used to determine the locations of the QTLs. The SMA revealed several markers from linkage group E significantly (P<0.05) associated with Sclerotinia stem rot resistance. With the CIM method, a QTL was identified near marker Satt185 on linkage group E in the 2005 greenhouse experiments. The QTL explained about 15.5% of the total phenotypic variance. The resistance allele of this QTL was from IA 2053. With the CIM method, another QTL was identified in the 2004 field experiment. The QTL is close to marker Satt212, which is also on linkage group E but is 11.5 cM away from marker Satt185. The QTL explained 53.1% of the total phenotypic variance. The resistance allele of this QTL was from PI 391589B.; The Asgrow 2506 with partial Sclerotinia stem rot resistance was crossed with another resistant cultivar NKS 19-90 to develop a mapping population of 140 F4 derived lines. The population was evaluated for Sclerotinia stem rot resistance in the field in 2001 and 2002 and in the greenhouse in 2002 and 2003. The population was also evaluated for genotypes with 53 polymorphic SSR markers. The SMA revealed that marker Sat_327 on linkage group C1 was significantly (P<0.05) associated with Sclerotinia stem rot resistance. The CIM method also identified one QTL located near marker Sat 327 on linkage group Cl, which explained about 12.2% of the total phenotypic variance. The resistance allele was from NKS 19-90. The QTLs identified can be used in maker assisted selection (MAS) in soybean breeding for Sclerotinia stem rot resistance.