Sunflower (Helianthus annuus L.) is one of the few crops native to the United States. The current USDA–ARS National Plant Germplasm System (NPGS) crop wild relatives sunflower collection is the largest extant collection in the world, containing 2519 accessions comprising 53 species—39 perennial and 14 annual. To fully utilize gene bank collections, however, researchers need more detailed information about the amount and distribution of genetic diversity present within the collection. The wild species are adapted to a wide range of habitats and possess considerable variability for most biotic and abiotic traits. This represents a substantial amount of genetic diversity available for many agronomic traits for cultivated sunflower, which has a very narrow genetic base. Sunflower ranked fifth highest among 13 crops of major importance to global food security surveyed from the mid-1980s to 2005 in the use of traits from crop wild relatives. The estimated annual economic contribution of the wild species for cultivated sunflower is between US$267 to 384 million. Most of the value is derived from the PET1 cytoplasm from wild H. petiolaris, disease resistance genes, abiotic salt tolerance, and resistance to imidazolinone and sulfonylurea herbicides. Crop wild relatives provide a wide range of valuable attributes for traditional and molecular breeding, as well as for ecological experimentation, and have enabled rapid advances in ecological and evolutionary genetics. The wild species of Helianthus continue to contribute specific traits to combat emerging pests and environmental challenges and, at the same time, are preserved for future generations. G.J. Seiler, L.L. Qi, USDA–ARS, Northern Crop Science Laboratory, 1605 Albrecht Blvd. N., Fargo, ND 58102-2765; L.F. Marek, North Central Regional Plant Introduction Station, Iowa State Univ. and USDA–ARS, 1305 State Ave., Ames, IA 50014. Received 4 Oct. 2016. Accepted 7 Dec. 2016. *Corresponding author (gerald.seiler@ars.usda. gov). Assigned to Associate Editor Heathcliffe Riday. Abbreviations: AFLP, amplified fragment length polymorphism; BSR, basal stalk rot; CMS, cytoplasmic male sterile; CWR, crop wild relatives; DM, downy mildew; EST, expressed sequence tags; HR, head rot; NPGS, National Plant Germplasm System; GRIN, Germplasm Resources Information System; MSR, mid-stalk rot; QTL, quantitative trait loci; SNP, single-nucleotide polymorphism; SSR, simple sequence repeat; SuMV, sunflower mosaic virus. Published in Crop Sci. 57:1083–1101 (2017). doi: 10.2135/cropsci2016.10.0856 © Crop Science Society of America | 5585 Guilford Rd., Madison, WI 53711 USA This is an open access article distributed under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Published June 16, 2017

Utilization of Sunflower Crop Wild Relatives for Cultivated Sunflower Improvement

A novel downy mildew resistance gene,
 Pl
 18
 , was introgressed from wild
 Helianthus
 argophyllus
 into cultivated sunflower and genetically mapped to linkage group 2 of the sunflower genome. The new germplasm, HA-DM1, carrying
 Pl
 18
 has been released to the public.
 Sunflower downy mildew (DM) 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 (Pl
 18
 ) 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 gene inheritance of resistance. Since no other Pl gene has been mapped to LG2, this gene was novel and designated as Pl
 18. SSR markers CRT214 and ORS203 flanked Pl
 18
 at a genetic distance of 1.1 and 0.4 cM, respectively. Forty-six single nucleotide polymorphism (SNP) markers that cover the Pl
 18 region were surveyed for saturation mapping of the region. Six co-segregating SNP markers were 1.2 cM distal to Pl
 18
 , and another four co-segregating SNP markers were 0.9 cM proximal to Pl
 18
 . The new BC2F4-derived germplasm, HA-DM1, carrying Pl
 18
 has been released to the public. This new line is highly resistant to all Plasmopara 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.

Genetics and mapping of a novel downy mildew resistance gene, Pl 18 , introgressed from wild Helianthus argophyllus into cultivated sunflower ( Helianthus annuus L.)

This article discusses changes in sunflower breeding objectives since the introduction of hybrid varieties 50 years ago. After a reminder of the importance of some early programmes, Canadian in particular, the present situation for each breeding objective is compared with those encountered earlier. Breeding for yield has changed from maximum possible yield under intensive agriculture to yield with resistance to abiotic stresses, moderate droughts and shallow soils in particular, helped by collaboration with agronomists to produce crop models. Breeding for oil has changed from quantity to quality and the value of seed meal is again becoming economically important. Necessary disease resistances vary with agronomic practises and selection pressure on pathogens according to varietal genetics. The possibilities of new types of sunflower are also discussed. Advances in genomics will change breeding procedures, but with rapidly changing molecular techniques, international collaboration is particularly important.

/pdf/changes-in-sunflower-breeding-over-the-last-fifty-years-1seakgcf2g.pdf

Changes in sunflower breeding over the last fifty years

Plant biotrophic oomycetes cause significant production problems and economic losses in modern agriculture and are controlled by fungicide applications and resistance breeding. However, high geneti...

Biological Characteristics and Assessment of Virulence Diversity in Pathosystems of Economically Important Biotrophic Oomycetes

Genotyping-by-sequencing revealed a new downy mildew resistance gene, Pl
 20
 , from wild Helianthus argophyllus located on linkage group 8 of the sunflower genome and closely linked to SNP markers that facilitate the marker-assisted selection of resistance genes.
 Downy mildew (DM), caused by Plasmopara halstedii, is one of the most devastating and yield-limiting diseases of sunflower. Downy mildew resistance identified in wild Helianthus argophyllus accession PI 494578 was determined to be effective against the predominant and virulent races of P. halstedii occurring in the United States. The evaluation of 114 BC1F2:3 families derived from the cross between HA 89 and PI 494578 against P. halstedii race 734 revealed that single dominant gene controls downy mildew resistance in the population. Genotyping-by-sequencing analysis conducted in the BC1F2 population indicated that the DM resistance gene derived from wild H. argophyllus PI 494578 is located on the upper end of the linkage group (LG) 8 of the sunflower genome, as was determined single nucleotide polymorphism (SNP) markers associated with DM resistance. Analysis of 11 additional SNP markers previously mapped to this region revealed that the resistance gene, named Pl
 20
 , co-segregated with four markers, SFW02745, SFW09076, S8_11272025, and S8_11272046, and is flanked by SFW04358 and S8_100385559 at an interval of 1.8 cM. The newly discovered P. halstedii resistance gene has been introgressed from wild species into cultivated sunflower to provide a novel gene with DM resistance. The homozygous resistant individuals were selected from BC2F2 progenies with the use of markers linked to the Pl
 20
 gene, and these lines should benefit the sunflower community for Helianthus improvement.

Genotyping-by-sequencing targeting of a novel downy mildew resistance gene Pl 20 from wild Helianthus argophyllus for sunflower ( Helianthus annuus L.)

Abstract The obligate biotrophic Oomycete, Plasmopara halstedii, causal agent of sunflower downy mildew, is capable of producing new pathogenic races over time. Although changes in the P. halstedii race composition were reviewed for the first time in 2007, since then the pathogen has continued to change its virulence character dramatically. There was a need, therefore, to update information on pathogenic diversity of P. halstedii by making accounts of the temporal and spacial changes in the pathogen populations in North and South America and Europe. This paper, based on current publications and personal communications, attempts to present an accurate overview of races in Europe and Americas for the last 7 years.

Denis Labrouhe Tourvieille

Papers

Recent Changes in the Pathogenic Variability of Plasmopara Halstedii (Sunflower Downy Mildew) Populations from Different Continents