Submitted to: Sunflower International Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: May 20, 2004
Publication Date: June 15, 2004
Citation: Hu, J., Chen, J., Gulya Jr, T.J., Miller, J.F. 2004. TRAP markers for a sunflower downy mildew resistance gene from a new Helianthus annuus source, PI 468435. International Sunflower Conference Proceedings. 16th International Sunflower Conference Proceedings, August 29-September 2, 2004, Fargo, ND. p. 623-630. Interpretive Summary: Downy mildew (DM) causes substantial yield losses of sunflower. Different genes conferring complete resistance to one or more DM races have been identified and are being incorporated into modern hybrids to combat this disease. However, the frequent emergence of new races of DM pathogen overcoming the resistance genes incorporated into modern hybrids poses a potential threat to sunflower production. One of our research activities is to look for new DM resistance sources and incorporate these new sources into cultivated sunflower germplasm. Using the segregating populations (F2 and BC1) derived from a cross between a elite sunflower line, HA 434 and a new DM resistance source, PI468435, we identified a TRAP marker associated with the DM resistance. This marker, a 257 bp (base pair) fragment, was amplified with primer combination of QHB18F12 and TRAP03. Primer QHB18F12 was designed from a sunflower EST (expressed sequence tag) that encodes a disease resistant protein, RPS2, cloned from the model plant Arabidopsis. The observation that this marker did not show variation in the segregating populations containing DM resistance genes, Pl6 and Pl8, suggests that the DM resistance gene in PI468435 is different. This marker can be used in a marker-assisted program to transfer the DM resistance gene from the wild H. annuus accession, PI 468435, into elite sunflower lines.
Technical Abstract: This paper reports the development of DNA markers associated with a downy mildew resistance gene from a new source, PI 468435, a Helianthus annuus L accession collected from Idaho, USA. We used the newly developed TRAP marker technique and segregating populations (F2 and BC1) derived from the cross between HA 434 and PI 468435. DM susceptibility of individual seedlings in the segregating populations was determined by both the presence of sporulation on the cotyledons after conventional seed immersion inoculation and the presence of DM-specific fragments amplified from the DNA extracted from the cotyledon of the inoculated seedlings prior to sporulation. Segregating data suggested that PI 468435 carries a dominant DM resistant gene. One fragment of 257 base pairs showed intensity variation and the variation was associated with the DM resistance phenotype in both F2 and BC1 populations. This fragment was amplified by a TRAP primer designed against a sunflower EST sequence, QHB18F12, which is homologous to the disease resistance gene, RPS2, cloned from Arabidopsis, in combination with an arbitrary primer, TRAP03. The same primer combination did not detect a similar variation in the segregating populations containing the Pl6 (from HA 335) and Pl8 (from HA 340) genes. This preliminary result implied that the DM resistant gene in PI 468435 was different from both the Pl6 and Pl8 genes.