Discovery and introgression of the wild sunflower-derived novel downy mildew resistance gene Pl in confection sunflower (Helianthus annuus L.).

A new downy mildew resistance gene, Pl , was identified from wild Helianthus annuus accession PI 435414, introduced to confection sunflower, and genetically mapped to linkage group 4 of the sunflower genome. Wild Helianthus annuus accession PI 435414 exhibited resistance to downy mildew, which is one of the most destructive diseases to sunflower production globally. Evaluation of the 140 BCF families derived from the cross of CMS CONFSCLB1 and PI 435414 against Plasmopara halstedii race 734 revealed that a single dominant gene controls downy mildew resistance in the population. Bulked segregant analysis conducted in the BCF population with 860 simple sequence repeat (SSR) markers indicated that the resistance derived from wild H. annuus was associated with SSR markers located on linkage group (LG) 4 of the sunflower genome. To map and tag this resistance locus, designated Pl , 140 BCF individuals were used to construct a linkage map of the gene region. Two SSR markers, ORS963 and HT298, were linked to Pl within a distance of 4.7 cM. After screening 27 additional single nucleotide polymorphism (SNP) markers previously mapped to this region, two flanking SNP markers, NSA_003564 and NSA_006089, were identified as surrounding the Pl gene at a distance of 0.6 cM from each side. Genetic analysis indicated that Pl is different from Pl , which had previously been mapped to LG4, but is closely linked to Pl . This new gene is highly effective against the most predominant and virulent races of P. halstedii currently identified in North America and is the first downy mildew resistance gene that has been transferred to confection sunflower. The selected resistant germplasm derived from homozygous BCF progeny provides a novel gene for use in confection sunflower breeding programs.