PAG-XIII  Plant & Animal Genomes XIII Conference

January 15-19, 2005
Town & Country Convention Center
San Diego, CA


P623 : Other Species

Development Of A PCR Marker For A Downy Mildew Resistance Gene Identified In A New Sunflower (Helianthus annuus) Source

Junfang Chen1 , Jerry F. Miller2 , Thomas J. Gulya2 , Brady A. Vick2 , Jinguo Hu2

1  Department of Plant Sciences, North Dakota State University, Fargo, ND 58105 USA
2  USDA-Agricultural Research Service, Northern Crop Science Laboratory,1307 North 18th Street, Fargo, ND, 58105 USA

Downy mildew (DM) is a devastating disease of sunflower, occurring in all sunflower growing regions of the world, except Australia. Studies have concluded that downy mildew resistance in sunflower is controlled by race-specific, single dominant genes denoted as Pl. Although about a dozen Pl genes have been reported up to now, the search for new Pl genes continues because new races of DM arise frequently. We have identified a new H. annuus DM resistance source, PI 468435, collected from Idaho, USA. Segregating data from both F2 and BC1 populations derived from the cross between HA434 and PI 468435 suggested that PI 468435 carries a dominant DM resistance gene. PCR with the allele specific primers revealed that the R gene in this new source is different from the reported Pl1/Pl6 and Pl5/Pl8 genes. Using the target region amplification polymorphism (TRAP) technique, we identified one fragment showing intensity variation. A strong intensity of this band was associated with the DM resistance phenotype in both the F2 and BC1 populations. This 257-bp fragment was amplified using the combination of an arbitrary primer, Trap03, and a fixed primer, QHB18F12. The latter primer was designed against a sunflower EST sequence which showed homology to the LRR (leucine rich repeat) domain of most plant disease resistance genes. With a view to develop a PCR marker for marker-assisted introgression of this new DM resistance gene into elite lines, we are in the process of converting this marker into STS by cloning and sequencing the 257 bp fragment.