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Abstract
Southern stem canker, caused by the fungus Diaporthe phaseolorum f. sp. meridionalis and Southern root-knot nematode (Meloidogyne incognita) (RKI), are two economically important diseases of soybean (Glycine max) in the southeastern USA. The stem canker resistance genes Rdc1, Rdc3, and Rdc? have been mapped using linkage analysis of genotypic data from simple sequence repeat (SSR) DNA markers and phenotypic data from greenhouse resistance screens. A new RKI resistance quantitative trait locus (QTL) in the soybean germplasm line G93-9009 has been linked to the T-locus for pubescence color using greenhouse resistance screens of two advanced backcross populations, BenningRR(5) x G93-9009 and BoggsRR(6) x G93-9009, that continued to segregate for pubescence color after phenotypic selection for RKI resistance of individual F2 plants following each cycle of backcrossing. Replicated field experiments were used to determine that RKI resistance from G93-9009 has been introgressed into these populations without yield reduction through linkage drag.