Submitted to: Theoretical and Applied Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/15/2000
Publication Date: N/A
Interpretive Summary: Root and stem rot is a fungal disease of soybean that causes many millions of dollars of crop loss each year. Having good molecular markers that 'tag' the genes conferring resistance to these diseases would be beneficial to plant breeders. This research team genetically mapped five of the genes using simple sequence repeats (SSRs). SSRs are markers that are cheap and easy to use, thus making them more useful to breeders. The results of this research mean that plant breeders can select for resistant plants by using laboratory procedures rather than cumbersome and time consuming inoculations. This means that resistant cultivars may be developed easier and more quickly.
Technical Abstract: Marker-assisted selection(MAS) can be used to manipulate disease-resistance genes in soybean cultivar development. Simple sequence repeats (SSRs) are convenient MAS markers because of single-locus inheritance and codominant multiple allelism. SSR linkages were desired for the Rps genes governing soybean plant resistance to Phytophthora root rot (Phytophthora megasperma Drechs f. sp. glycinea Kuan and Ervin. Near-isogenic lines (NILs) of Clar or Williams, each homozygous resistant (RpsRps) at just one of those Rps loci, were mated to an E2 (late-maturing) NIL of Harosoy, which is homozygous susceptible (rpsrps) at all six loci. From 100 to 120 F2:3 progenies obtained from each mating, 20 random F3 seedlings were evaluated for resistance (R) or susceptibility (S) following inoculation with the race of P. megasperma corresponding to the segregating Rps allele. F2 individuals classified as homozygous resistant (RpsRps), and as homozygous susceptible (rpsrps), were used to create contrasting DNA bulks. Linkage to the given Rps allele was presumed if an SSR marker displayed polymorphism between the two bulks. Putative linkages were confirmed or refuted by an SSR assay of F2 individuals within each homozygous class. Recombination values were computed by applying maximum likelihood equations to the SSR allelic segregation data. SSRs on linkage groups (Lgs)N, J, F, and G were identified with linkages to Rps1, Rps2, Rps3, and Rps4, respectively. A skewed segregation of R:S phenotypes in the Rps5 population precluded the detection of linked SSRs. The Rps6 locus, whose map position was heretofore unknown, was linked with three SSRs in a region of LG-G that contains Rps4 and may also contain Rps5.