Characterization and mapping of a downy mildew resistance gene, Pl36, in sunflower (Helianthus annuus L.)

Authors: Qi, Lili; Cai, Xiwen

Submitted to: Molecular Breeding
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/24/2022
Publication Date: 2/5/2022
Citation: Qi, L., Cai, X. 2022. Characterization and mapping of a downy mildew resistance gene, Pl36, in sunflower (Helianthus annuus L.). Molecular Breeding. 42. Article 8. https://doi.org/10.1007/s11032-022-01280-1.
DOI: https://doi.org/10.1007/s11032-022-01280-1

Interpretive Summary: The pathogen that causes sunflower downy mildew (DM) disease is found in North America and in other sunflower-growing countries and has been responsible for widespread yield losses in sunflower. Studying regional disease spread and the change of the DM pathogen population is important for the development of new sunflower inbred lines with resistance to the existing DM pathogen. Using a plant line that contains a known DM resistance gene is a prerequisite to identify pathogen races. The sunflower line 803-1 has been used as a differential line to study the interaction of plant and DM pathogens. However, the DM resistance gene in 803-1 is unknown. In this study, we genetically mapped the DM resistance gene in 803-1 and named the gene Pl36. Pl36 is located on sunflower chromosome 13 and is resistant to the most prevalent DM races tested, providing a resistant source for use in sunflower breeding.

Technical Abstract: Downy mildew (DM) is one of the most serious diseases in sunflower-growing regions worldwide, often significantly reducing sunflower yields. The causal agent of sunflower DM, the oomycete pathogen Plasmopara halstedii, is highly virulent and aggressive. Studying regional disease spread and virulence evolution in the DM pathogen population is important for the development of new sunflower inbred lines with resistance to the existing DM pathogen. The sunflower line 803-1, as one of nine international differential hosts, has been used in the identification of P. halstedii virulent pathotypes in sunflower since 2000. The DM resistance gene in 803-1 was temporally designated Pl5+ based on allelic analysis but has not been molecularly characterized. In the present study, bulked segregant analysis and genetic mapping confirmed the presence of the Pl gene within a large gene cluster on sunflower chromosome 13 in 803-1, as previously reported. Subsequent saturation mapping in the gene target region with single nucleotide polymorphism (SNP) markers placed this gene at an interval of 3.5 Mb in the XRQ reference genome assembly, a location different from that of Pl5. Therefore, the Pl gene in 803-1 was re-designated Pl36 because it is not allelic with Pl5. Four SNP markers co-segregated with Pl36, and SNP SFW05743 was 1.1 cM proximal to Pl36. The relationship of eight DM R genes in the cluster is discussed based on their origin, map position, and specificity of resistance/susceptibility to DM infection.