Submitted to: Journal of Theoretical and Applied Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 19, 1998
Publication Date: N/A
Interpretive Summary: The soybean cyst nematode (SCN), Heterodera glycines Ichinohe, is a devastating pest of soybean and is responsible for significant losses in yield in the USA. SCN causes root necrosis, reduced nodulation and decreased shoot vigor. Several attempts have been made to identify molecular markers (DNA) closely linked to genes conferring SCN resistance so that the markers can be used to help identify resistant plants in breeding programs. We identified a molecular marker, pBLT65, close to a DNA locus conferring resistance to race 3 of the SCN. The marker is useful in that it can be used to track the inheritance SCN resistance locus in marker assisted breeding schemes. This paper describes a faster method based on the polymerase chain reaction for identifying markers derived from the original marker, pBLT65. These markers also are closely linked to the same SCN resistance gene. These new molecular markers can be identified faster than previous methods, therefore they should be useful to soybean breeders in marker assisted breeding schemes to distinguish between progeny with a high likelihood of possessing resistance to SCN.
pBLT65 is a 450 nt soybean cDNA encoding a portion of the bifunctional enzyme aspartokinase-homoserine dehydrogenase (AK-HSDH). pBLT65 maps within 3.5 cM of Rhg4 locus conferring resistance to race 3 of the soybean cyst nematode and maps within 3.5 cM of the i locus conferring pigmented seed coat on linkage group A depending upon the mapping population used. PCR reactions are easier and less time-consuming than RFLP mapping, and therefore, would be valuable in marker assisted breeding programs to select progeny with the Rhg4 allele. DNA primers were synthesized from genomic DNA sequences encoding a soybean AK-HSDH for use in polymerase chain reactions to identify DNA polymorphisms that would correlate closely with the inheritance of Rhg4 or rhg4.. PCR amplification of DNA from the soybean cultivar Peking (Rhg4) yielded three DNA fragments, 1a (1160 bp), 1b (1146 bp) and 3 (996 bp). Amplification of DNA from the cultivar Kent (rhg4) yielded DNA fragments 2 (1020 bp), 3 (996 bp) and 4 (960 bp). Fragments 1a, 1b, 2 and 4 were also polymorphic between the soybean lines PI 290136 and BARC-2(Rj4). Therefore, a segregating population of 131 F2 and F3 plants derived from the cross PI 290136 X BARC-2 (Rj4) was used to map the PCR polymorphisms and the i locus. The nucleotide sequence of fragments 1b, 3 and 4 were determined. All polymorphic fragments mapped adjacent to the Rhg4 locus. Our mapping indicates the Rhg4 locus is adjacent to loci represented by these bands and all are adjacent to the i locus controlling seed coat pigmentation on linkage group A.