Facilitating breeding for resistance to southern stem canker and elevated seed oleic acid content in soybean
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Disease resistance and seed oil composition are two economically important aspects of soybean (Glycine max) production in the southeastern USA. Soybean resistance to Southern stem canker caused by the fungus Diaporthe phaseolorum f. sp. meridionalis and methods of selection for elevated seed oleic acid content have been studied in these experiments. The stem canker resistance genes Rdc2, Rdc3, Rdc4, and Rdc?(PI398469) have been mapped using linkage analysis of phenotypic data from greenhouse resistance screens and genotypic data from simple sequence repeat (SSR) and single nucleotide polymorphism (SNP) DNA markers. Two genes, Rdc2 from D85-10412 and Rdc4 from Dowling both mapped to Gm02, but are located at different regions of the chromosome. The other two genes, Rdc3 from Crockett and Rdc?(PI398469) from PI 398469 mapped to a similar location on Gm14 and appear to be clustered with several genes with known disease resistance motifs. All four resistance genes have mapped less than 3 cM from SSR or SNP markers that may be suitable for marker assisted selection. In addition to mapping disease resistance genes, three methods of selecting single plants with the elevated oleic acid trait from breeding line N00-3350 have been compared. They include phenotypic selection (PS) using gas chromatography, stratified phenotypic selection (SPS) using gas chromatography while stratifying based on maturity, and marker assisted selection (MAS) using SNP markers associated with oleic acid quantitative trait loci. The three selection methods were tested in three different populations, BoggsRR x N00-3350, H7242RR x N00-3350, and PrichardRR x N00-3350. Stratified phenotypic selection and MAS were found to be more effective than PS when oleic acid QTL and maturity were segregating within a population. Plants selected using SPS and MAS gave rise to lines with higher average oleic acid and avoided a shift towards earlier maturity that was observed in some cases with PS. Maturity was significantly negatively correlated with oleic acid content in two of the three populations.