Introgression and targeting of the Pl37 and Pl38 genes for downy mildew resistance from wild Helianthus annuus and H. praecox into cultivated sunflower (Helianthus annuus L.)

Authors: Qi, Lili; Talukder, Md Zahirul; MA, GUOJIA - North Dakota State University; SEILER, GERALD - Former ARS Employee

Submitted to: Theoretical and Applied Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/31/2023
Publication Date: 3/23/2023
Citation: Qi, L., Talukder, M.I., Ma, G., Seiler, G. 2023. Introgression and targeting of the Pl37 and Pl38 genes for downy mildew resistance from wild Helianthus annuus and H. praecox into cultivated sunflower (Helianthus annuus L.). Theoretical and Applied Genetics. 136. Article 82. https://doi.org/10.1007/s00122-023-04316-y.
DOI: https://doi.org/10.1007/s00122-023-04316-y

Interpretive Summary: Global sunflower production is hampered by several biotic stresses, including downy mildew (DM) disease, which is responsible for significant yield losses in epidemically favorable weather. The use of hybrids carrying DM resistance genes has been proven to be the most effective and economical approach to control this disease. For over 50 years, breeding for resistance to DM has relied on the introgression of new genes from wild species to achieve sustained DM control. In this study, we report the introgression and molecular mapping of two new DM resistance genes from wild sunflower species, Helianthus annuus and H. praecox, into cultivated sunflower. The DM resistance gene from wild H. annuus, designated Pl37, was mapped to sunflower chromosome 4, while the DM resistance gene from wild H. praecox, designated Pl38, was mapped to sunflower chromosome 2. Multi-race DM tests revealed that lines with Pl37 or Pl38 are immune to the most prevalent and virulent DM races. Two germplasm lines, HA-DM15 with Pl37 and HA-DM16 with Pl38, were developed for use in sunflower DM-resistance breeding with accompanying molecular markers allowing for more efficient tagging and selection when incorporating these genes into elite sunflower lines for developing sunflower hybrids with effective and durable resistance to DM.

Technical Abstract: Downy mildew (DM), caused by the oomycete Plasmopara halstedii (Farl.) Berl. & de Toni, is known as the most prevalent disease occurring in global sunflower production areas, especially in North America and Europe. In this study, we report the introgression and molecular mapping of two new DM resistance genes from wild sunflower species, Helianthus annuus and H. praecox, into cultivated sunflower. Two mapping populations were developed from the crosses of HA 89/H. annuus PI 435417 (Pop1) and CMS HA 89/H. praecox PRA-417 (Pop2). The phenotypic evaluation of DM resistance/susceptibility was conducted in the BC1F2-derived BC1F3 populations using P. halstedii race 734. The BC1F2 segregating Pop1 was genotyped using an Optimal GBS AgriSeqTM Panel consisting of 768 mapped SNP markers, while the BC1F2 segregating Pop2 was genotyped using a genotyping-by-sequencing approach. Linkage analysis and subsequent saturation mapping placed the DM resistance gene, designated Pl37, derived from H. annuus PI 435417 in a 1.68 cM genetic interval on sunflower chromosome 4. Pl37 co-segregated with SNP markers SPB0003 and C4_5738736. Similarly, linkage analysis and subsequent saturation mapping placed the DM resistance gene, designated Pl38 derived from H. praecox PRA-417 in a 0.8 cM genetic interval on sunflower chromosome 2. Pl38 co-segregated with seven SNP markers. Multi-pathotype tests revealed that lines with Pl37 or Pl38 are immune to the most prevalent and virulent P. halstedii races tested. Two germplasm lines, HA-DM15 with Pl37 and HA-DM16 with Pl38, were developed for use in sunflower DM-resistance breeding.