Genome mapping of soybean cyst nematode resistance genes in 'Peking', PI 90763, and PI 88788 using DNA markers

Several sources of soybean cyst nematode (Heterodera glycines Ichinohe; SCN) resistance have been identified in soybean [Glycine max (L.) Merrill]; yet, the genetic basis of this economically important trait remains poorly characterized. This study was conducted to identify quantitative trait loci that control disease response in three commonly used sources of SCN resistance. Using genetic markers, we analyzed three segregating soybean F₂ populations ['Evans' x 'Peking', Evans x Plant Introduction (PI) 90763, and Evans x PI 887881 and compared the results with those of a previous study involving PI 209332. For the Peking, PI 90763, and PI 209332 populations, races 1, 3, and 6 were used as SCN inoculum; for the PI 88788 population, only races 3 and 6 were used. To uncover putative resistance loci, F₂ DNA marker genotypes at between 63 and 99 loci in each population were contrasted with cyst indices averaged from 12 F(2:3) progeny individuals. Four independent partial SCN resistance loci were uncovered at P < 0.0002 (probability per locus). One of these loci, located at the top of linkage group 'G' near RFLP locus C006V, was significant at P < 0.0001 in all populations and races tested. Other significant loci included one near RFLP A378H at the opposite end of linkage group 'G' from C006V, another on linkage group 'J' near marker B032V-l, and a fourth on linkage group 'N' near marker A280Hae-l. Comparisons between different SCN races indicated that some of the putative resistance loci behave in a race-specific manner. These results may serve as a resource for SCN researchers and soybean breeders by summarizing a wide range of genetic data on the soybean-SCN interaction.