|CAI, XIWEN - North Dakota State University|
|GULYA, THOMAS - Retired ARS Employee|
Submitted to: Theoretical and Applied Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/13/2015
Publication Date: 3/21/2016
Citation: Qi, L.L., Foley, M.E., Cai, X.W., Gulya, T.J. 2016. Genetics and mapping of a novel downy mildew resistance gene, Pl18, introgressed from wild Helianthus argophyllus into cultivated sunflower (Helianthus annuus L.). Theoretical and Applied Genetics. 129:741-752. doi:10.1007/s00122-015-2662-2.
Interpretive Summary: Sunflower downy mildew (DM) is the most destructive foliar disease and has spread to every major sunflower-growing country of the world, except Australia. The disease can cause up to 80% yield loss in sunflower production. Current fungicides for seed treatment are only partially effective as preventative measures, and there are no foliar curative fungicides. The use of resistant hybrids, where available, is the most efficient measure for controlling downy mildew. A new DM resistance gene, Pl18, was transferred from the wild species Helianthus argophyllus into cultivated sunflowers. Molecular mapping located this gene on linkage group 2 of the sunflower genome, which is different from all known DM resistance genes in sunflower. A new germplasm (HA-DM1) that carries Pl18 was released to the public. This line is highly resistant to all of the DM physiological pathotypes identified in the USA to date and will provide breeders with an effective and unique source of resistance against downy mildew in sunflower. The DNA markers that were developed will be especially useful for marker-assisted selection and pyramiding of Pl resistance genes in sunflower breeding programs.
Technical Abstract: Sunflower downy mildew is considered to be the most destructive foliar disease that has spread to every major sunflower-growing country of the world, except Australia. A new dominant downy mildew resistance gene (Pl18) transferred from wild Helianthus argophyllus (PI 494573) into cultivated sunflower was mapped to linkage group (LG) 2 of the sunflower genome using bulked segregant analysis with 869 simple sequence repeat (SSR) markers. Phenotyping 142 BC1F2:3 families derived from the cross of HA 89 and H. argophyllus confirmed the single genic inheritance of resistance. Since no other Pl gene has been mapped to LG2, this gene was novel and designated as Pl18. SSR markers CRT214 and ORS203 flanked Pl18 at a genetic distance of 1.1 and 0.4 cM, respectively. Forty-six single nucleotide polymorphism (SNP) markers that cover the Pl18 region were surveyed for saturation mapping of the region. Six co-segregating SNP markers were 1.2 cM distal to Pl18, and another four co-segregating SNP markers were 0.9 cM proximal to Pl18. The new BC2F4-derived germplasm, HA-DM1, carrying Pl18 has been released to the public. This new line is highly resistant to all P. halstedii races identified in the USA providing breeders with an effective new source of resistance against downy mildew in sunflower. The molecular markers that were developed will be especially useful in marker-assisted selection and pyramiding of Pl resistance genes because of their close proximity to the gene and the availability of high-throughput SNP detection assays.