Sclerotinia stem rot [caused by Sclerotinia sclerotiorum (Lib) de Bary] is an economically important disease of soybean [Glycine max (L.) Merr] and no soybean cultivars show complete resistance to the disease. To screen soybean cultivars and lines for resistance to this disease, three related but independent studies were conducted in the greenhouse and laboratory. In the first study, 392 F4:6 recombinant inbred lines (RILs) from seven populations were evaluated for resistance to S. sclerotiorum by drop- and spray-mycelium methods under the greenhouse conditions. Individual lines in two of seven populations evaluated by drop-mycelium method were significantly different (P<0.0500). Parental polymorphism was tested with 132 simple sequence repeat (SSR) markers associated with Sclerotinia stem rot resistance in other studies and 97 polymorphic markers were used to test the progenies from the seven populations. Sixteen markers showed high correlations with the phenotypic data in the seven populations. In the second study, 66 plant introductions (PIs) were evaluated with the drop-mycelium method and significant (p < 0.0050) differences were found among the PIs for resistance to Sclerotinia stem rot. In the third study, drop-mycelium, spray-mycelium, and field evaluation methods were compared in terms of correlation of the data. The data from drop-mycelium inoculation had strong correlations with that from spray-mycelium (R2 = 0.63, P< 0.0005) and field evaluations (R2 = 0.40, P<0.0381) for resistance to Sclerotinia stem rot.
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