A genetic balancing act: Exploring segregation distortion of SCN resistance in soybean [Glycine max (L.) Merr.]

Rhg1 is the most important locus conferring resistance to soybean cyst nematode (SCN; Heterodera glycine Ichinohe) in soybean [Glycine max (L.) Merr.]. Previous research has shown that to obtain viable plants, the SCN resistance allele at Rhg1 on chromosome 18 needs to be paired with NSF_RAN07, an atypical resistance-associated NSF allele of the N-ethylmaleimide sensitive factor (NSF) gene on chromosome 07. This causes segregation distortion in populations developed from crosses between resistant and susceptible plants. Our study aimed to improve our understanding of this segregation distortion and determine the developmental stage at which it occurs. DNA from developing F₂ seeds and F₂ plants originating from crosses between resistant and susceptible parents was genotyped with markers for the rhg1 and NSF loci using TaqMan assays. Chi-square tests revealed significant deviations from the expected Mendelian segregation ratio (1:2:1:2:4:2:1:2:1) in both F₂ seeds and plants, indicating segregation distortion at these loci. The absence of the rhg1-b_rhg1-b_NSF_Ch07_NSF_Ch07 genotype supports the previous finding that the combination of the resistance allele rhg1-b and the commonly occurring NSF_Ch07 allele is lethal, apparently because the α-SNAP (where SNAP is soluble NSF attachment protein) encoded by rhg1-b or rhg1-a interacts well with the NSF_RAN07 protein but not the more common NSF_Ch07 protein. The findings indicate that segregation distortion occurs prior to seed maturation and is primarily due to zygotic selection during early seed development. The results emphasize the need to consider this genetic interaction in breeding efforts to improve soybean since segregation distortion may affect the inheritance of SCN resistance and other traits linked to Rhg1 or NSF_Ch07.