Marker-Assisted Breeding for Pyramiding Multiple Resistances to Soybean Fungal Diseases

Fungal diseases such as soybean stem canker (SSC), frogeye leaf spot (FLS), and sudden death syndrome (SDS) cause substantial yield losses in the soybean crop worldwide. This study aimed to pyramid major resistance genes and QTLs against these diseases through marker-assisted backcrossing (MABC). Diagnostic SSR markers, linked to Rdm4 (SSC), Rcs3 (FLS), and SDS resistance QTLs, were validated and successfully employed for foreground and background selection in crosses between the elite cultivar A8100RR and the resistant donor ‘Forrest’. Molecular analyses confirmed the effective introgression and fixation of multiple resistance loci in BC₂F₅ lines. Under artificial inoculation, lines R30-11 and R25-13 displayed high resistance levels to Diaporthe aspalathi, Cercospora sojina, Fusarium virguliforme, and F. tucumaniae. Genotype R30-11 exhibited the most consistent resistance across pathogens, while R25-13 combined multi-disease resistance with glyphosate tolerance and stable agronomic performance comparable to commercial cultivars. These results provide the first evidence of successful pyramiding of major resistance genes and QTLs to multiple fungal diseases in soybean through MABC. The developed lines represent valuable germplasm for breeding programs, targeting durable and sustainable disease management.