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.

Specimens of 110 unrelated individuals were collected from Han ethnic group in Jiangsu Province of China. DNA was extracted from blood specimens using Chelex 100 method. (1) Amplifications were carried out by using reagents provided in DNA examining Kit (Codon Biotechnology CD., LTD, China) and using a Mastercycler gradiend 5331 (Eppendorf AG, Hamburg, Germany) according to the technical manual. The amplified products were separated denaturing polyacrylamide gel electrophoresis with continuous buffer system and visualized by silver staining. Data were analyzed using POWERSTATS software (2). A modified 2-test was used to verify whether the genetype distribution conformed to Hardy-Weinberg equilibrium predictions (3).