Abstract
Lines of sunflower (Helianthus annuus L.) resistant to race 3 of downy mildew, incited by Plasmopara halstedii (Farl.) Berl. et de Toni, were developed and inheritance of this resistance was determined. The same single, dominant gene controlled resistance in selections developed from two open‐pollinated sources, ‘Novinka’ and ‘Progress’, in crosses with the breeding lines, HA 89 and RHA 274. This gene did not impart resistance to race 2. A breeding line, RF‐S11‐5566‐74‐10, obtained from Romania was reported to have a new gene, Pl5, imparting resistance to downy mildew. Selections of this line were resistant to race 3. The F2 seedlings of crosses between RF‐S11‐5566‐74‐10 and the selections of Novinka and Progress did not segregate when plants were inoculated with race 3, indicating that all three sources possess the same gene, Pl5, imparting resistance to race 3 downy mildew. The findings have implications for sunflower breeding in the USA, as hybrids must have the gene Pl2, controlling resistance to race 2, and the new gene, Pl5, to provide resistance to both races.
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