Ten Broad Spectrum Resistances to Downy Mildew Physically Mapped on the Sunflower Genome.

Yann Pecrix (1) , Charlotte Penouilh-Suzette (1) , Stephane Munos (1) , Felicity Vear (2) , Laurence Godiard (1)

1 LIPM - Laboratoire des interactions plantes micro-organismes
2 GDEC - Génétique Diversité et Ecophysiologie des Céréales

Resistance to downy mildew (Plasmopara halstedii) in sunflower (Helianthus annuus L.) is conferred by major resistance genes, denoted Pl. Twenty-two Pl genes have been identified and genetically mapped so far. However, over the past 50 years, wide-scale presence of only a few of them in sunflower crops led to the appearance of new, more virulent pathotypes (races) so it is important for sunflower varieties to carry as wide a range of resistance genes as possible. We analyzed phenotypically 12 novel resistant sources discovered in breeding pools derived from two wild Helianthus species and in eight wild H. annuus ecotypes. All were effective against at least 16 downy mildew pathotypes. We mapped their resistance genes on the sunflower reference genome of 3,600 Mb, in intervals that varied from 75 Kb to 32 Mb using an AXIOMR genotyping array of 49,449 SNP. Ten probably new genes were identified according to resistance spectrum, map position, hypersensitive response to the transient expression of a P. halstedii RXLR effector, or the ecotype/species from which they originated. The resistance source HAS6 was found to carry the first downy mildew resistance gene mapped on chromosome 11, whereas the other resistances were positioned on chromosomes 1, 2, 4, and 13 carrying already published Pl genes that we also mapped physically on the same reference genome. The new genes were designated Pl23–Pl32 according to the current nomenclature. However, since sunflower downy mildew resistance genes have not yet been sequenced, rules for designation are discussed. This is the first large scale physical mapping of both 10 new and 10 already reported downy mildew resistance genes in sunflower

Mots clés: Helianthus annuus; Plasmopara halstedii; resistance gene (R gene); SNP array; oomycete; RXLR; effector; hypersensitive response (HR); crop protection; resistance to diseases

Mots clés: mildiou du tournesol; résistance aux maladies; pathologie végétale

Domaines: Microbiologie et Parasitologie; Phytopathologie et phytopharmacie

Yann Pecrix, Charlotte Penouilh-Suzette, Stephane Munos, Felicity Vear, Laurence Godiard. Ten Broad Spectrum Resistances to Downy Mildew Physically Mapped on the Sunflower Genome.. Frontiers in Plant Science, 2018, 9 (1780), pp.1-15. ⟨10.3389/fpls.2018.01780⟩. ⟨hal-01990160⟩