Transgressive inheritance of broad-spectrum resistance to Heterodera glycines and Meloidogyne incognita in soybean chromosome segment substitution lines

Soybean cyst nematode ( Heterodera glycines , SCN) and southern root-knot nematode ( Meloidogyne incognita , RKN) are major limitation to soybean production, with few resistance sources available. Using 199 and 177 chromosome segment substitution lines (CSSLs) derived from Glycine max cv. Suinong14 and G. soja accession ZYD00006, we evaluated resistance to SCN HG type 1.2.3.5.6.7 (race 4) and RKN race 1, and compared the loci with those previously mapped for SCN HG type 2.5.7 (race 5). Despite both parents being susceptible, many CSSLs exhibited resistance levels exceeding both parents, while others showed extreme susceptibility, demonstrating strong transgressive segregation. QTL mapping identified 6 FI-associated and 9 CGR-associated loci for SCN race 4, and 17–25 significant loci for RKN across two inoculum levels. Single resistance loci generally conferred only moderate effects, but the combination of multiple favorable alleles from both parents produced higher resistance. Comparative analysis revealed several shared QTL intervals among SCN races 4 and 5 and RKN race 1, suggesting partial common genetic control. These findings demonstrate that pyramiding multiple loci from wild and cultivated soybean can generate transgressive inheritance, producing resistant lines beyond parental performance and offering valuable targets for breeding durable, broad-spectrum nematode resistance.